The Clinicopathologic Spectrum of Posttransplantation Lymphoproliferative Disorders

By Tsao, Lawrence Hsi, Eric D

Context.-Posttransplantation lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid proliferations occurring in the setting of solid organ or bone marrow transplantation. They show a clinical, morphologic, and molecular genetic spectrum ranging from reactive polyclonal lesions to frank lymphomas. The close association with Epstein-Barr virus has been established and the pathogenetic role of this virus is becoming better understood. Although they are relatively uncommon, PTLDs are a significant cause of morbidity and mortality in transplant patients. Objective.-To review the incidence, risk factors, clinical features, pathogenesis, and classification of PTLDs.

Data Sources.-We reviewed relevant articles indexed in PubMed (National Library of Medicine), with emphasis on more recent studies. The classification of PTLDs is based on the most current World Health Organization classification text.

Conclusions.-Posttransplantation lymphoproliferative disorders are a heterogeneous group of disorders showing a wide clinical and morphologic spectrum. Although relatively uncommon, PTLDs represent a serious complication after transplantation. Many risk factors for PTLD are well established, including transplanted organ, age at transplant, and Epstein-Barr virus seronegativity at transplant. However, other factors have been implicated and still require additional examination. Recent studies are shedding some light on the pathogenesis of PTLDs and defining relevant pathways related to Epstein-Barr virus. As the pathogenesis of PTLDs is further elucidated, the classification of PTLDs will most likely evolve.

(Arch Pathol Lab Med. 2007;131:1209-1218)

Posttransplantation lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid proliferations occurring in the setting of solid organ or bone marrow transplantation. It has long been known that intact immune systems are required for antitumor surveillance. The occurrence of lymphoma in immunosuppressed transplantation patients was first recognized in 1968 and its close association with Epstein-Barr virus (EBV) infection followed.1,2 Today we recognize a spectrum of lymphoid proliferations ranging from reactive polyclonal lesions to frank lymphomas. The close association with EBV is well described and the pathogenetic role of this virus is beginning to be understood. However, not all PTLDs are EBV driven, and a significant subset of EBV-negative PTLDs have been identified.3,4 Although PTLDs represent a relatively uncommon complication in transplant patients, they are a significant cause of morbidity and mortality in these patients. Because of variability in clinical, histopathologic, and immunophenotypic presentations, the diagnosis and classification of PTLDs can be difficult. In this review, we will consider the incidence, risk factors, clinical features, pathogenesis, and histopathology of this group of lymphoproliferative disorders.

EPIDEMIOLOGY

Incidence

Although there is significant variation in the reported incidences of PTLD after solid organ and bone marrow transplantation, the overall incidence is less than 2% of transplanted patients.5 There is a clear association between the incidence of PTLD and type of transplantation, with the highest incidence in the first year after transplantation. 6 Among the most commonly transplanted solid organs, cardiac, lung, and hepatic transplantation show the highest incidences of PTLD, ranging from 2% to 5%,7-9 2% to 3%,10,11 and 2% to 5%,12-14 respectively. The incidence after pancreatic transplantation was recently reported to be 2.1%.15 Renal transplants show a much lower incidence of PTLD at approximately 1%.16,17 This may be because of the generally lower intensity of immunosuppression required compared with that of other vital organs. The incidence of PTLD after bone marrow transplantation ranges from 0.5% to 1.0%.18,19 In recent larger series, the incidence of PTLD appears to be lower than previously cited, possibly the result of better management of immunosuppression (Table 1). Because of the higher risk of PTLD in children (discussion follows), studies examining pediatric populations will generally report incidences 2- to 3-fold higher than in adults.

Risk Factors

Several risk factors for the development of PTLD have been identified (Table 2). These include type of organ transplanted, immunosuppressive drugs, age of the patient, and EBV status pretransplantation. As previously noted, the incidence of PTLD varies by transplanted organ, with the renal transplants having the lowest incidence, heart transplants having intermediate incidence, and heart-lung or multivisceral transplantation generally having the highest incidence.20 Large collaborative databases have defined relative risks of PTLD for major organ types.6 Specific biologic factors may account for these differences. For example, lung and intestinal transplants typically include the highest amount of lymphoid tissue, which may increase the EBV infection rates. Relative ease of mucosal biopsies in these sites may also raise the incidence of early PTLD detection.

The variation in the incidence between the different types of transplanted organs may also be related to varying degrees of immunosuppression necessary for each organ. Specific drugs have been implicated as high-risk factors. In the early days of transplant, use of the potent immunosuppressive OKT3 resulted in a marked increase in PTLDs in cardiac transplant.21 Use of cyclosporine also increased the incidence of PTLD; however, this could be reduced by careful therapeutic monitoring to avoid overimmunosuppression. 22,23 Although immunosuppression is a major risk factor, it is still unclear whether the contribution is due to the cumulative dose or peak levels of drugs. Some studies, unable to identify any specific agents, have suggested the cumulative immunosuppressive dose to be the contributory factor.24-27 In bone marrow transplantation, T- cell depletion of the donor bone marrow is a well-known risk factor for PTLD.28-30 However, studies of newer immunosuppressive agents targeting T cells have not always conclusively demonstrated similar increased risk in solid organ transplantations.24 Experience with these newer immunosuppressive agents may help define the magnitude of risk for a PTLD associated with their use.

Mismatch of EBV status in the recipient and donor (seronegative recipient with seropositive donor) is another well-known risk factor for PTLD and is intimately associated with the pathogenesis of PTLD.26-33 In one striking study of a single institution’s experience with solid organ transplantation, seronegative patients had a 76-fold risk of PTLD compared with seropositive patients.34 The higher risk associated with EBV-naive patients also explains, to some extent, the higher incidence of PTLD among pediatric transplant patients.35 Not surprisingly, EBV-naive patients will frequently present initially with EBV-associated PTLD of the early lesion or polymorphic type, possibly representing an abnormal primary EBV response in these immunosuppressed patients.

A patient’s underlying disease has been suggested in some series to be a risk factor for PTLD. Primary immunodeficiency showed a 2.5- fold increased risk in one bone marrow transplant series.18 Patients with hepatitis C infection, 9,36 autoimmune hepatitis,37 cystic fibrosis,38 and Langerhans cell histiocytosis39 have also been suggested to be at higher risk for PTLD. Other infectious agents including cytomegalovirus,27,40 human herpes virus 8,41 and, recently, simian virus 4042 have all been reported in cases of PTLD and may contribute to increased risk. The number and severity of rejection episodes and degree of HLA mismatching have also been examined as risk factors. However, the magnitude of risk these factors pose is still controversial.

Innate host immune responses may also play a role in the development of PTLD. Cytokine gene polymorphisms associated with regulation of cytokine production during immune responses are being examined. Specifically, there is some evidence that low interferon gamma production may be associated with increased risk of PTLD in liver and renal transplant patients.43,44

CLINICAL FEATURES

The clinical presentation of PTLD is highly variable, depending on the type of immunosuppression, type of allograft, and histologic type of PTLD (early lesions, polymorphic PTLD, or monomorphic PTLD). Patients may present with infectious mononucleosis-like symptoms. There is frequent involvement of the tonsillar tissue and Waldeyer ring, especially in pediatric patients. Such PTLDs often have the histology of so-called early lesions. Monomorphic PTLD, like lymphoma, can present with constitutional symptoms, lymphadenopathy, and mass lesions. Up to 25% of patients may present with allograft failure due to involvement by PTLD. In these patients, the clinical presentation can mimic allograft rejection. In bone marrow transplants, widespread involvement is common and may simulate graft- versus-host disease. Bone marrow involvement may present with new- onset or persistent cytopenias. Polymorphic PTLD may present with features overlapping early lesions and monomorphic PTLD. As a result of the variability of presentation, a high index of suspicion must be present in any patient with a history of transplantation. PATHOGENESIS

Investigations have yielded insight into the pathogenesis of PTLD. Phenotypic and immunoglobulin mutational studies have resulted in a model of histogenesis for PTLD. Molecular studies have supported this model and have identified several genes thought to be important in molecular pathogenesis. Epstein-Barr virus infection, of course, plays a central role in development of PTLD and recent work has also elucidated important mechanisms of oncogenesis relevant to these proliferations.

Histogenesis

Like B-cell non-Hodgkin lymphomas, molecular and phenotypic features of PTLD have been compared with normal B-cell counterparts. Analysis of immunoglobulin heavy chain variable (IGHV) genes is a powerful tool in determining the maturational state of B cells. According to this model, unmutated (germline) genes represent antigen-naive (pregerminal center or virgin) B cells, and B cells harboring somatic hypermutation have been exposed to the germinal center (GC) microenvironment and thus represent GC or post-GC B cells.45 Approximately 25% of polymorphic PTLDs and 10% of diffuse large B-cell lymphomas (DLBLs) have unmutated (germline) IGHV. Burkitt lymphoma (BL) and 25% of centroblastic DLBL show ongoing somatic hypermutation, consistent with GC B cells. The majority of polymorphic (75%) and monomorphic (65%) PTLDs show somatic hypermutation that is stable among clones, suggesting a late GC or post-GC phenotype. Thus, most PTLDs derive from GC or post-GC cells.46 The few PTLDs that lack somatic hypermutation appear to arise early after transplantation and are EBVassociated. They may derive from true pre-GC cells or cells that are incapable of undergoing the GC reaction.46 A recent study that analyzed both immunoglobulin heavy and light chain genes showed that 94% of PTLDs had somatic hypermutation.47

Further phenotypic characterization into GC and post-GC stages using Bcl-6 (GC marker), MUM1 (late GC and post-GC), and CD138 (post- GC, terminal differentiation) has resulted in the model shown in Figure 1.46 The Bcl-6+/MUM1/CD138 PTLDs derive from cells experiencing the GC reaction. They harbor ongoing mutations and morphologically correspond often to centroblastic types of DLBL or BL. A Bcl-6/MUM1+/CD138 phenotype corresponds to PTLDs that derive from B cells that have completed the GC reaction and include most (65%) polymorphic and some (30%) monomorphic PTLDs, particularly DLBL with immunoblastic features. This phenotype is uncommon in human immunodeficiency virus-related lymphoma. 48,49 A third phenotype, Bcl-6/MUM1+/CD138+, represents post-GC cells and includes polymorphic or monomorphic PTLDs showing immunoblastic DLBL morphology or plasmacytic differentiation.

Antigen Stimulation and Viral Oncogenesis

Analysis of immunoglobulin gene usage provides evidence that specific antigen stimulation and selection may not play a major role in the pathogenesis. In an analysis of 50 PTLDs, no preferential use of IGHV family genes was noted, suggesting a lack of specific pathogenetic antigen. Evidence of antigen selection in tumor cells based on replacement mutations in the complementarity determining regions of the immunoglobulin heavy chain gene (IGH) was seen in less than 30% of cases.47 In fact, up to 50% of PTLDs have lost the ability to express functional immunoglobulin.47-51

Epstein-Barr virus infection, in the setting of immunosuppression, has a central role in the pathogenesis of PTLD. Several lines of evidence can be offered. It is present in almost all PTLDs that occur early after transplant. 52,53 It is also frequently clonally integrated in tumor cells of polymorphic and monomorphic PTLDs, indicating that it was present at the time of malignant transformation. 54 Increasing EBV titers can also be detected in the blood of patients prior to development of PTLD and treatment with EBV-specific T cells can result in tumor reduction. 55-59 Finally, EBV latent genes have transforming activity in B cells. In fact, EBV has been found to transform GC cells lacking immunoglobulin.60 The exact mechanism of viral oncogenesis is yet to be elucidated; however, EBV latent membrane proteins (LMP), LMP-1 and LMP-2A, have been the focus of attention. These oncogenic proteins activate intracellular signaling pathways, mimicking CD40 (a member of the tumor necrosis factor receptor family) and B-cell receptor signals.61 Latent membrane protein 1 has been shown in PTLD tissue to mimic activated tumor necrosis factor receptor family members through tumor necrosis factor receptor-associated factors. This results in downstream activation of NFkappaB, an important transcription factor that activates prosurvival genes.62,63

Although most PTLDs are EBV related, approximately 20% of patients with PTLD will lack evidence of EBV in their tumors, and the incidence may be increasing.3 The EBV-positive and EBV-negative PTLDs show differences in clinical course and may represent independent entities. 3,4 Specifically, EBV-negative PTLDs appear to occur late after transplantation, are more often classified as monomorphic compared with EBV-positive PTLDs, and generally have an aggressive course. However, some will still respond to decreased immunosuppression. Given the relative rarity of these tumors, the pathogenesis of these EBV-negative PTLDs is still poorly understood. Currently, the question of whether these are better considered coincidental lymphomas or part of the heterogeneity of PTLDs remains unanswered.

Genetic Alterations

Several genetic alterations in oncogenes or tumor suppressor genes have been found in PTLDs. These include MYC, BCL6, NRAS, and TP53.64-66 Chromosomal translocations involving MYC and mutations in MYC, BCL6, NRAS, and TP53 have been described.64-66 Alterations in MYC, NRAS, and TP53 are uncommon and seen only in monomorphic (immunoblastic lymphoma histology) or multiple myeloma types of PTLDs and are never present in polymorphic lesions.66 Rearrangement of BCL6 is very uncommon in PTLD as opposed to DLBL in immunocompetent patients. However, BCL6 mutations are common (approximately 50%), and have been associated with shorter survival and nonresponsiveness to reduced immunosuppression. 64 Rearrangements of MYC have also been associated with more aggressive disease and poor outcome.67 Microsatellite instability has been described in a higher proportion of PTLDs than in non-Hodgkin lymphoma from immunocompetent hosts, corresponding to the high degree of genetic instability in PTLDs.68

Recently, epigenetic alterations have been examined. In particular, hypermethylation of O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair gene, has been found in 60% of monomorphic PTLD. Inactivation of MGMT has been shown to be lymphomagenic in knockout mice and may promote genetic instability with acquisition of TP53 and RAS mutations.69,70 Other genes identified as abnormally methylated include death-associated protein kinase (DAPK1), a proapoptotic molecule, and TP73, a putative tumor suppressor gene related to TP53.69 Much work remains to be done and new tools such as arraybased comparative genomic hybridization studies have identified other abnormalities.71 However, the exact role of these abnormalities in the development of PTLD remains largely unknown.

Donor Versus Host Origin

Studies on the cell of origin of PTLD have shown that at least 90% of PTLDs originate from host B cells in solid organ transplantation.72 The converse is true for bone marrow transplantation.73 Although donor-derived PTLDs have been reported with increased incidence in liver and lung transplants, with suggestions of predilection for involving the graft, recent studies have been controversial. 72-76 The prognostic significance of donor versus hostderived PTLD is unclear.76 In addition, there have been no large-scale studies examining T-cell and natural killer (NK) cell PTLDs.

PATHOLOGIC FEATURES AND CLASSIFICATION

Classification of PTLD is currently based on the World Health Organization (WHO) system for classifying hematopoietic neoplasms.77 The key morphologic, immunophenotypic, and molecular characteristics of each type of PTLD are listed in Table 3. The WHO divides PTLD into 4 major categories: early lesions, polymorphic PTLD, monomorphic PTLD, and Hodgkin lymphoma (HL) and HL-like PTLD. Early lesions, polymorphic PTLD, and monomorphic PTLD represent a pathologic spectrum that can be observed synchronously or metachronously within a single specimen or within multiple specimens from a single patient.

Early Lesions

Early lesions consist of 2 morphologic types: plasmacytic hyperplasia and infectious mononucleosis-like PTLD. The common defining characteristic of early lesions is some degree of preservation of the underlying architecture of the involved tissue (Figure 2, A). Plasmacytic hyperplasia is a lesion characterized by numerous plasma cells with rare immunoblasts. Infectious mononucleosis-like lesions resemble typical infectious mononucleosis, with marked paracortical expansion by a mixed T-cell and plasma cell infiltrate and a prominent immunoblastic proliferation. Some early lesions may show overlapping features between plasmacytic hyperplasia and infectious mononucleosis-like lesions.

Immunophenotyping of early lesions is of limited diagnostic utility as it will confirm the morphologic impression of variable mixtures of B cells, T cells, and plasma cells with polytypic light chain expression. Immunoblasts will frequently show evidence of EBV infection using in situ hybridization for EBV-encoded RNA (EBER) or EBV LMP-1 immunohistochemical stain. Other EBV-associated nuclear antigens (ie, EBV-encoded nuclear antigen, LMP) are not reliably expressed.78 As the name implies, early lesions represent the earliest morphologic and genotypic changes of PTLD.66 These lesions occur early (<1 year) in the course of transplantation and are more common in EBV-naive pediatric and adult transplant recipients. Analysis of IGH and episomal EBV genome will frequently yield polyclonal or oligoclonal patterns. Occasionally, a minor clone is seen, but is of no clinical significance. Clonal cytogenetic changes are rare in early lesions.67,79 Polymorphic Lesions

Polymorphic PTLD is characterized by a mixed lymphoproliferation consisting of immunoblasts, plasma cells, and intermediate-sized lymphoid cells. In contrast to early lesions, polymorphic PTLD is characterized by destruction of the underlying architecture of the involved tissue (Figure 2, B). However, in contrast to monomorphic PTLD, polymorphic PTLD shows a full spectrum of B cells from small to intermediate-sized lymphocytes to immunoblasts and mature plasma cells (Figure 2, C). Atypia, necrosis, and numerous mitotic figures are all acceptable. In the past, these features of ”malignancy” were used to distinguish ”polymorphic lymphoma” from ”polymorphic hyperplasia.” 80 However, subdividing polymorphic PTLD is no longer necessary under the WHO classification because recent findings revealed that morphologic subdivision does not reliably predict clinical behavior.66,81 Immunophenotyping of polymorphic PTLD will show variable mixtures of B cells and T cells. Analysis of surface or cytoplasmic immunoglobulin expression is useful for identifying monotypic B-cell populations. However, B cells may show polytypic immunoglobulin expression in polymorphic PTLD. Most polymorphic PTLDs will show EBV latency II and III patterns, expressing EBER and EBV-LMP-1 with variable expression of EBV-encoded nuclear antigen 2 and other viral antigens.78 Although immuno-phenotyping may appear polytypic, molecular analysis of IGH or episomal EBV genome will usually show a clonal pattern.52,81 Clonal cytogenetic changes may be present.67,79

Monomorphic Lesions

Monomorphic PTLDs are characterized by architectural and cytologic atypia sufficient to be classified as a lymphoma based on morphologic features.77 In general, monomorphic PTLDs show invasion and architectural effacement by large aggregates and confluent sheets of transformed cells with large nuclei with prominent nucleoli (Figure 2, D and E). The neoplastic cells can show marked pleomorphism or plasmacytoid/plasma cell differentiation. These cases of monomorphic PTLD generally are not diagnostically problematic. However, occasional cases of PTLD may span the spectrum of polymorphic PTLD and monomorphic PTLD. These cases are difficult to classify within a single category. The presence of areas of monomorphic PTLD, however, should always be clearly indicated.

Monomorphic PTLDs are divided according to B-cell or T-cell lineage and further subclassified according to the WHO classification of lymphomas in the nontransplant population.77 It is beyond the scope of this review to include a detailed description of the WHO classification of lymphomas, so only a general description will be included with areas of difficulty highlighted.

Monomorphic B-cell PTLD (B-PTLD) is the prototypic monomorphic PTLD. The majority of the B-PTLDs will resemble DLBL in nontransplant patients. Morphologic variants include immunoblastic, centroblastic, and, less commonly, anaplastic morphology. However, as with DLBL, there does not appear to be any clinical significance associated with these morphologic variants. Morphologic resemblance to BL or atypical BL is diagnostically significant and should be confirmed with immunophenotypic and cytogenetic studies. Immunophenotypic analysis will show expression of B-cell antigens or a BL phenotype in cases of BL or atypical BL. Antigens aberrantly expressed by conventional DLBL (ie, CD43, Bcl-2) may be present. Surface immunoglobulin expression may be monotypic or absent. Currently, the evaluation of GC or post-GC phenotype is not required because the clinical and prognostic implications are still uncertain.45-48 The majority of BPTLDs show presence of EBV infection within the transformed cells, with variable latency patterns.82 Virtually all cases show a clonal pattern of IGH rearrangement and, if present, episomal EBV genomes. Cytogenetic evaluation will show clonal karyotypic abnormalities, which can include trisomies 9 and/or 11 and abnormalities of 8q24.1, 3q27, and 14q32.67

Rare cases of B-PTLD are morphologically and immunophenotypically identical to plasma cell neoplasms (Figure 2, F).83,84 Plasma cell myeloma and plasmacytoma-like PTLD can also be EBV associated in about 50% of the cases reported.83,84 Clinically, these can present as rare extramedullary plasmacytic neoplasms similar to plasmacytomas or plasma cell myeloma. Plasma cell PTLDs need to be differentiated from plasmacytic hyperplasia, a non-destructive early lesion, and DLBL with marked plasmacytic differentiation, a monomorphic PTLD. Because of the rarity of plasma cell PTLD, it is currently unclear if plasma cell directed, B-cell directed, or both, is the most effective therapy. The evaluation for urine and serum M components, serum immunoglobulin levels, and lytic bone lesions, although not always conclusive, can be helpful in the diagnosis of plasma cell myeloma-PTLD.83 Immunophenotypic evaluation of B-PTLD should include B-cell and plasma cell-associated antigens.

T-cell PTLDs (T-PTLDs) are all classified as monomorphic PTLDs and must show a similar degree of architectural and cytologic atypia required for B-PTLD (Figure 2, G). The T-PTLDs are subclassified according to the WHO classification for T-cell neoplasms in the nontransplant setting. Immunophenotyping is essential for diagnosis and subtyping of T-PTLD. Depending on the subtype, the immunophenotype will vary. Evaluation of pan-T-cell antigens, although not always conclusive, is useful for demonstrating any aberrant losses of expression. CD4 or CD8 expression and alphabeta or gammadelta T-cell receptor expression will follow what is generally known for T-cell lymphomas in nonimmunosuppressed patients. Markers of immaturity (CD1a, TdT, and CD34) can be seen in cases of precursor T lymphoblastic lymphoma. CD30 expression can be present, especially in the anaplastic large cell lymphoma subtypes. CD56 and cytotoxic markers can be expressed by T-PTLD. Most (60%- 80%) T-PTLDs lack EBV; however, a minor subset may be EBV positive.85 Molecular analysis of the T-cell receptor (TCR) gene should show a clonal pattern. Analysis of episomal EBV genome is usually not indicated, but will show a clonal pattern when EBV is present. True NK-cell PTLD will frequently express CD56 and cytotoxic markers, but must lack surface CD3. Variable expression of pan-T-cell antigens, CD2 and CD7, can be seen. Unlike T-PTLD, the vast majority (80%-90%) of true NK-cell PTLD shows EBV infection with clonal episomal EBV genome.86 Molecular analysis of TCR must show a germline pattern to be diagnosed as a true NKcell PTLD.

Hodgkin Lymphoma and Hodgkin Lymphoma-like Lesion

Hodgkin lymphoma and HL-like PTLD is a rare category of PTLD that is classified independently from other monomorphic PTLDs. Hodgkin lymphoma PTLD shows the morphologic features characteristic of classic HL in nontransplant patients. These include the proper background inflammatory infiltrate and Reed-Sternberg cells. Hodgkin lymphoma-PTLD must be distinguished from polymorphic PTLD with Reed- Sternberg-like cells. Hodgkin lymphoma-PTLD has Reed-Sternberg cells with the classic HL phenotype (CD45 , CD3 , CD20/weak+, CD15+/, CD30+). These cases usually arise late in transplantation and frequently show evidence of EBV infection. Although currently HL and HL-like PTLD are considered similar, there is evidence suggesting that HL-like PTLD may be more related clinically and pathologically to a monomorphic B-cell PTLD.87 The HL-like PTLD frequently shows an atypical immunophenotype for HL such as strong expression of CD20.

Low-Grade B-Cell Lymphoproliferative Disorders

The current WHO classification does not recognize lowgrade B- cell lymphoproliferative disorders as PTLD. However, they do occur in the posttransplant setting. Extranodal marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue (MALT) type occurring as PTLDs morphologically and immunophenotypically resemble their counterparts in immuncompetent patients (Figure 2, H and I).88,89 These MALT lymphomas do not show evidence of EBV, but are frequently associated with Helicobacter organisms, especially in gastric sites.88 Molecular analysis of IGH will show a clonal pattern.89 Other low-grade B-cell lymphoproliferative disorders reported after transplantation include hairy cell leukemia.90 This is extremely rare. Clinically, morphologically, and immunophenotypically, these cases are identical to those seen in the nontransplant setting and may represent coincidental events.

Clinical Course

The clinical course of PTLD is highly variable and dependent on the type of PTLD, the lineage of the PTLD, and the association with EBV. Virtually all early lesions regress with reduction in immunosuppression and generally show good prognosis, especially in pediatric patients. 81,91 About half of polymorphic PTLDs regress with reduction of immunosuppression; however, some will progress, requiring chemotherapy.19,81 Of those progressing, more than half will respond to therapy.81 Some studies have found the presence of BCL6 gene mutations to predict poor response to reduction of immunosuppression.64 The majority of monomorphic PTLDs do not regress with reduction of immunosuppression alone. In addition, some monomorphic PTLDs do not show good response even to chemotherapy.81 Among the monomorphic PTLDs, EBVassociated PTLDs consistently have a better prognosis when compared with EBV-negative PTLDs.3,4 However, a minor subset, up to one-third, of EBV-negative PTLDs have been reported to regress with reduction of immunotherapy. 3 Monomorphic PTLDs of T-cell/NK-cell lineage almost never regress with reduction of immunosuppression alone and respond poorly to chemotherapy. Hodgkin lymphoma and HL-like PTLDs usually arise late after transplantation (>1 year). The prognosis of HL and HL-like PTLDs appears relatively good. In one large study, none of 60 patients developing HL and HL-like-PTLD died of PTLD-associated causes.84

The low-grade B-cell lymphoproliferative disorders, specifically MALT lymphomas, are also usually seen late after transplantation (>1 year).88,89 Clinically, the MALT lymphomas behave indolently. The majority of cases can be managed by eradication of the Helicobacter organisms and conservative management (localized radiation, surgery, and single-agent chemotherapy).88,89 The rare cases of hairy cell leukemia reported after transplantation have shown an indolent course and excellent response to conventional hairy cell leukemia therapy.90

DIAGNOSIS

The timely and accurate diagnosis of PTLD is essential for early intervention. However, a high clinical index of suspicion is required. Recently, monitoring and quantification of EBV viral load in peripheral blood has been shown to be helpful in predicting the development of PTLDs. Although clear guidelines have yet to be established regarding laboratory procedures and management, the trends are clear. Persistently low EBV viral load has good negative predictive value for development of EBVpositive PTLD. The EBV levels appear to increase prior to PTLD and fall after successful therapy.92 In an attempt to define important thresholds, a level of 200 copies/105 leukocytes was shown to correlate with symptomatic EBV infection or PTLD in pediatric transplant patients.93,94 Some investigators have also suggested preemptive therapy with agents such as rituximab.95,96 However, because not all patients with elevated levels develop PTLD and EBV-negative PTLDs cannot be predicted with such a test, further work is needed to precisely define the role of EBV viral load testing in transplant patient populations.97,98 Recent studies have suggested using cytokine genotyping in addition to EBV viral loads to increase the predictive value for PTLDs.99

PATHOLOGIC EVALUATION: WHAT NEEDS TO BE DONE?

Practically speaking, excisional biopsies of masses or enlarged lymph nodes are preferred because one of the characteristic differentiating features between early lesions and polymorphic and monomorphic PTLD relies on the ability to document preservation of underlying architecture. Extranodal disease is common. Involved sites may include the gastrointestinal tract, liver, lung, and bone marrow. If endoscopic or needle biopsies are used, several biopsies or passes are advised to obtain adequate tissue for ancillary studies.

When multiple sites of involvement are present, sampling of several lesions should be considered as early, polymorphic, and monomorphic lesions can be synchronously present in different sites. In addition, because synchronous lesions may actually represent different clonal proliferations, separate work-up at the genetic level (ie, molecular analysis of IGH gene) may be of interest for follow-up purposes.100 In patients with allograft involvement where rejection enters into the clinical differential diagnosis, allograft biopsies can help differentiate rejection from PTLD. Assessment of EBV can be helpful because PTLDs are often positive, whereas EBV is absent in rejection. Overall, focusing the diagnostic evaluation on the basis of organ dysfunction or a mass lesion provides the highest yield for obtaining adequate tissue for diagnosis. Screening blood or bone marrow evaluations in patients suspected of PTLD is usually of low diagnostic yield.

Immunophenotyping PTLDs is essential because of the significant differences in prognosis and therapy between B-cell and NK/T-cell lymphomas. Evaluation for presence of EBV by immunohistochemical or molecular techniques is also essential because of the differences in prognosis between the EBV-positive and EBV-negative cases. The EBER in situ hybridization is preferred, given its presence in all latency patterns. Although not absolutely required for diagnosis in the majority of cases, testing for clonality (usually by antigen receptor-rearrangement studies) is also helpful for complete characterization and can be used for comparison to simultaneous or future PTLDs. A distinct clone at a later date would suggest a new independent PTLD rather than a relapse. Cytogenetic studies, also not necessary, similarly may be helpful. Assessment of oncogene mutations or translocations, by molecular or cytogenetic techniques, is currently not routinely performed. Diagnostically, the type of PTLD, lineage of the PTLD (if a monomorphic lesion), clonal status, and EBV status should be clearly indicated in the pathology report.

Table 2. Risk Factors for Posttransplantation Lymphoproliferative Disorders

Transplanted organ (multivisceral > lung > liver > heart > kidney)

Pediatric age group

Epstein-Barr virus seronegativity

Immunosuppressive drugs/regimen (OKT3)

Underlying host disease

Cytokine gene polymorphisms

References

1. Starzl TE. Discussion of Murray JE, Wilson RE, Tilney NL, et al. Five years’ experience in renal transplantation with immunosuppressive drugs: survival, function, complications and the role of lymphocyte depletion by thoracic duct fistula. Ann Surg. 1968;168:416.

2. Briggs JD, Canavan JS, Dick HM, et al. Influence of HLA matching and blood transfusion on renal allograft survival. Transplantation. 1978;25:80-85.

3. Nelson BP, Nalesnik MA, Bahler DW, et al. Epstein-Barr virus- negative posttransplant lymphoproliferative disorders: a distinct entity? Am J Surg Pathol. 2000; 24:375-385.

4. Leblond V, Davi F, Charlotte F, et al. Posttransplant lymphoproliferative disorders not associated with Epstein-Barr virus: a distinct entity? J Clin Oncol. 1998; 16:2052-2059.

5. Dharnidharka VR, Tejani AH, Ho PL, Harmon WE. Post-transplant lymphoproliferative disorder in the United States: young Caucasian males are at highest risk. Am J Transplant. 2002;2:993-998.

6. Opelz G, Dohler B. Lymphomas after solid organ transplantation: a collaborative transplant study report. Am J Transplant. 2004;4:222-230.

7. Swerdlow AJ, Higgins CD, Hunt BJ, et al. Risk of lymphoid neoplasia after cardiothoracic transplantation. a cohort study of the relation to Epstein-Barr virus. Transplantation. 2000;69:897- 904.

8. Webber SA, Naftel DC, Fricker FJ, et al. Lymphoproliferative disorders after paediatric heart transplantation: a multi- institutional study. Lancet. 2006;367: 233-239.

9. Buda A, Caforio A, Calabrese F, et al. Lymphoproliferative disorders in heart transplant recipients: role of hepatitis C virus (HCV) and Epstein-Barr virus (EBV) infection. Transpl Int. 2000;13(suppl 1):S402-S405.

10. Reams BD, McAdams HP, Howell DN, et al. Posttransplant lymphoproliferative disorder: incidence, presentation, and response to treatment in lung transplant recipients. Chest. 2003;124:1242- 1249.

11. Ramalingam P, Rybicki L, Smith MD, et al. Posttransplant lymphoproliferative disorders in lung transplant patients: the Cleveland Clinic experience. Mod Pathol. 2002;15:647-656.

12. Norin S, Kimby E, Ericzon BG, et al. Posttransplant lymphoma- a singlecenter experience of 500 liver transplantations. Med Oncol. 2004;21:273-284.

13. Kremers WK, Devarbhavi HC, Wiesner RH, et al. Post- transplant lymphoproliferative disorders following liver transplantation: incidence, risk factors and survival. Am J Transplant. 2006;6:1017-1024.

14. Jain A, Nalesnik M, Reyes J, et al. Posttransplant lymphoproliferative disorders in liver transplantation: a 20-year experience. Ann Surg. 2002;236:429-437.

15. Paraskevas S, Coad JE, Gruessner A, et al. Posttransplant lymphoproliferative disorder in pancreas transplantation: a single- center experience. Transplantation. 2005;80:613-622.

16. Caillard S, Lelong C, Pessione F, et al. Post-transplant lymphoproliferative disorders occurring after renal transplantation in adults: report of 230 cases from the French Registry. Am J Transplant. 2006;6:2735-2742.

17. Martin-Gomez MA, Pena M, Cabello M, et al. Posttransplant lymphoproliferative disease: a series of 23 cases. Transplant Proc. 2006;38:2448-2450.

18. Bhatia S, Ramsay NK, Steinbuch M, et al. Malignant neoplasms following bone marrow transplantation. Blood. 1996;87:3633-3639.

19. Curtis RE, Travis LB, Rowlings PA, et al. Risk of lymphoproliferative disorders after bone marrow transplantation: a multi-institutional study. Blood. 1999; 94:2208-2216.

20. Cockfield SM. Identifying the patient at risk for post- transplant lymphoproliferative disorder. Transpl Infect Dis. 2001;3:70-78.

21. Swinnen LJ, Costanzo-Nordin MR, Fisher SG, et al. Increased incidence of lymphoproliferative disorder after immunosuppression with the monoclonal antibody OKT3 in cardiac-transplant recipients. N Engl J Med. 1990;323:1723-1728.

22. Beveridge T, Krupp P, McKibbin C. Lymphomas and lymphoproliferative lesions developing under cyclosporin therapy. Lancet. 1984;1:788.

23. Starzl TE, Nalesnik MA, Porter KA, et al. Reversibility of lymphomas and lymphoproliferative lesions developing under cyclosporin-steroid therapy. Lancet. 1984;1:583-587.

24. Birkeland SA, Hamilton-Dutoit S. Is posttransplant lymphoproliferative disorder (PTLD) caused by any specific immunosuppressive drug or by the transplantation per se? Transplantation. 2003;76:984-988.

25. Brouwer RM, Balk AH,WeimarW. Occurrence of lymphoproliferative disorder after heart transplantation is related to the total immunosuppressive load. Transpl Int. 1992;5(suppl 1):S259-S261.

26. Allen UD, Farkas G, Hebert D, et al. Risk factors for post- transplant lymphoproliferative disorder in pediatric patients: a case-control study. Pediatr Transplant. 2005;9:450-455.

27. Katz BZ, Pahl E, Crawford SE, et al. Case-control study of risk factors for the development of post-transplant lymphoproliferative disease in a pediatric heart transplant cohort. Pediatr Transplant. 2007;11:58-65. 28. Curtis RE, Travis LB, Rowlings PA, et al. Risk of lymphoproliferative disorders after bone marrow transplantation: a multi-institutional study. Blood. 1999; 94:2208-2216.

29. Antin JH, Bierer BE, Smith BR, et al. Selective depletion of bone marrow T lymphocytes with anti-CD5 monoclonal antibodies: effective prophylaxis for graft-versus-host disease in patients with hematologic malignancies. Blood. 1991; 78:2139-2149.

30. Gerritsen EJ, Stam ED, Hermans J, et al. Risk factors for developing EBV-related B cell lymphoproliferative disorders (BLPD) after non-HLA-identical BMT in children. Bone Marrow Transplant. 1996;18:377-382.

31. Sundin M, Le Blanc K, Ringden O, et al. The role of HLA mismatch, splenectomy and recipient Epstein-Barr virus seronegativity as risk factors in posttransplant lymphoproliferative disorder following allogeneic hematopoietic stem cell transplantation. Haematologica. 2006;91:1059-1067.

32. Wigle DA, Chaparro C, Humar A, et al. Epstein-Barr virus serology and posttransplant lymphoproliferative disease in lung transplantation. Transplantation. 2001;72:1783-1786.

33. Haque T, Thomas JA, Falk KI, et al. Transmission of donor Epstein-Barr virus (EBV) in transplanted organs causes lymphoproliferative disease in EBV-seronegative recipients. J Gen Virol. 1996;77:1169-1172.

34. Walker RC, Paya CV, Marshall WF, et al. Pretransplantation seronegative Epstein-Barr virus status is the primary risk factor for posttransplantation lymphoproliferative disorder in adult heart, lung, and other solid organ transplantations. J Heart Lung Transplant. 1995;14:214-221.

35. Guthery SL, Heubi JE, Bucuvalas JC, et al. Determination of risk factors for Epstein-Barr virus-associated posttransplant lymphoproliferative disorder in pediatric liver transplant recipients using objective case ascertainment. Transplantation. 2003;75:987-993.

36. Hezode C, Duvoux C, Germanidis G, et al. Role of hepatitis C virus in lymphoproliferative disorders after liver transplantation. Hepatology. 1999;30: 775-778.

37. Shpilberg O, Wilson J, Whiteside TL, Herberman RB. Pre- transplant immunological profile and risk factor analysis of post- transplant lymphoproliferative disease development: the results of a nested matched case-control study. The University of Pittsburgh PTLD Study Group. Leuk Lymphoma. 1999;36:109-121.

38. Cohen AH, Sweet SC, Mendeloff E, et al. High incidence of posttransplant lymphoproliferative disease in pediatric patients with cystic fibrosis. Am J Respir Crit Care Med. 2000;161:1252- 1255.

39. Newell KA, Alonso EM, Kelly SM, et al. Association between liver transplantation for Langerhans cell histiocytosis, rejection, and development of posttransplant lymphoproliferative disease in children. J Pediatr. 1997;131:98-104.

40. Manez R, Breinig MC, Linden P, et al. Posttransplant lymphoproliferative disease in primary Epstein-Barr virus infection after liver transplantation: the role of cytomegalovirus disease. J Infect Dis. 1997;176:1462-1467.

41. Kapelushnik J, Ariad S, Benharroch D, et al. Post renal transplantation human herpesvirus 8-associated lymphoproliferative disorder and Kaposi’s sarcoma. Br J Haematol. 2001;113:425-428.

42. Vilchez RA, Jauregui MP, Hsi ED, et al. Simian virus 40 in posttransplant lymphoproliferative disorders. Hum Pathol. 2006;37:1130-1136.

43. Nalesnik MA, Zeevi A, Randhawa PS, et al. Cytokine mRNA profiles in Epstein-Barr virus-associated post-transplant lymphoproliferative disorders. Clin Transplant. 1999;13:39-44.

44. Bidwell J, Keen L, Gallagher G, et al. Cytokine gene polymorphism in human disease: on-line databases. Genes Immun. 1999;1:3-19.

45. Kuppers R, Klein U, Hansmann ML, Rajewsky K. Cellular origin of human B-cell lymphomas. N Engl J Med. 1999;341:1520-1529.

46. Capello D, Rossi D, Gaidano G. Post-transplant lymphoproliferative disorders: molecular basis of disease histogenesis and pathogenesis. Hematol Oncol. 2005;23:61-67.

47. Capello D, Cerri M, Muti G, et al. Analysis of immunoglobulin heavy and light chain variable genes in post-transplant lymphoproliferative disorders. Hematol Oncol. 2006;24:212-219.

48. Capello D, Cerri M, Muti G, et al. Molecular histogenesis of posttransplantation lymphoproliferative disorders. Blood. 2003;102:3775-3785.

49. Carbone A, Gloghini A, Larocca LM, et al. Expression profile of MUM1/IRF4, BCL-6, and CD138/syndecan-1 defines novel histogenetic subsets of human immunodeficiency virus-related lymphomas. Blood. 2001;97:744-751.

50. Brauninger A, Spieker T, Mottok A, et al. Epstein-Barr virus (EBV)-positive lymphoproliferations in post-transplant patients show immunoglobulin V gene mutation patterns suggesting interference of EBV with normal B cell differentiation processes. Eur J Immunol. 2003;33:1593-1602.

51. Timms JM, Bell A, Flavell JR, et al. Target cells of Epstein- Barr-virus (EBV)-positive post-transplant lymphoproliferative disease: similarities to EBV-positive Hodgkin’s lymphoma. Lancet. 2003;361:217-223.

52. Nalesnik MA, Jaffe R, Starzl TE, et al. The pathology of posttransplant lymphoproliferative disorders occurring in the setting of cyclosporine A-prednisone immunosuppression. Am J Pathol. 1988;133:173-192.

53. Swinnen LJ. Diagnosis and treatment of transplant-related lymphoma. Ann Oncol. 2000;11(suppl 1):45-48.

54. Cleary ML, Nalesnik MA, Shearer WT, Sklar J. Clonal analysis of transplantassociated lymphoproliferations based on the structure of the genomic termini of the Epstein-Barr virus. Blood. 1988;72:349- 352.

55. Riddler SA, Breinig MC, McKnight JL. Increased levels of circulating Epstein-Barr virus (EBV)-infected lymphocytes and decreased EBV nuclear antigen antibody responses are associated with the development of posttransplant lymphoproliferative disease in solid-organ transplant recipients. Blood. 1994;84:972-984.

56. Tsai DE, Nearey M, Hardy CL, et al. Use of EBV PCR for the diagnosis and monitoring of post-transplant lymphoproliferative disorder in adult solid organ transplant patients. Am J Transplant. 2002;2:946-954.

57. Bollard CM, Savoldo B, Rooney CM, Heslop HE. Adoptive T-cell therapy for EBV-associated post-transplant lymphoproliferative disease. Acta Haematol. 2003;110:139-148.

58. Haque T, Taylor C,Wilkie GM, et al. Complete regression of posttransplant lymphoproliferative disease using partially HLA- matched Epstein Barr virus-specific cytotoxic T cells. Transplantation. 2001;72:1399-1402.

59. Nalesnik MA, Rao AS, Furukawa H, et al. Autologous lymphokine- activated killer cell therapy of Epstein-Barr virus-positive and – negative lymphoproliferative disorders arising in organ transplant recipients. Transplantation. 1997; 63:1200-1205.

60. Bechtel D, Kurth J, Unkel C, Kuppers R. Transformation of BCR- deficient germinal-center B cells by EBV supports a major role of the virus in the pathogenesis of Hodgkin and posttransplantation lymphomas. Blood. 2005;106:4345-4350.

61. Mancao C, Altmann M, Jungnickel B, HammerschmidtW. Rescue of ”crippled” germinal center B cells from apoptosis by Epstein-Barr virus. Blood. 2005; 106:4339-4344.

62. Ramalingam P, ChuW-S, Tubbs R, Rybicki L, Pettay J, Hsi ED. Latent membrane protein 1, tumor necrosis factor receptor- associated factor (TRAF) 1, TRAF-2, TRAF-3, and nuclear factor kappa B expression in posttransplantation lymphoproliferative disorders. Arch Pathol Lab Med. 2003;127:1335-1339.

63. Siegler G, Kremmer E, Gonnella R, Niedobitek G. Epstein-Barr virus encoded latent membrane protein 1 (LMP1) and TNF receptor associated factors (TRAF): colocalisation of LMP1 and TRAF1 in primary EBV infection and in EBV associated Hodgkin lymphoma. Mol Pathol. 2003;56:156-161.

64. Cesarman E, Chadburn A, Liu YF, et al. BCL-6 gene mutations in posttransplantation lymphoproliferative disorders predict response to therapy and clinical outcome. Blood. 1998;92:2294-2302.

65. Delecluse HJ, Rouault JP, Jeammot B, et al. Bcl6/Laz3 rearrangements in post-transplant lymphoproliferative disorders. Br J Haematol. 1995;91:101-103.

66. Knowles DM, Cesarman E, Chadburn A, et al. Correlative morphologic and molecular genetic analysis demonstrates three distinct categories of posttransplantation lymphoproliferative disorders. Blood. 1995;85:552-565.

67. Djokic M, Le Beau MM, Swinnen LJ, et al. Post-transplant lymphoproliferative disorder subtypes correlate with different recurring chromosomal abnormalities. Genes Chromosomes Cancer. 2006;45:313-318.

68. Duval A, Raphael M, Brennetot C, et al. The mutator pathway is a feature of immunodeficiency-related lymphomas. Proc Natl Acad Sci U S A. 2004;101: 5002-5007.

69. Rossi D, Gaidano G, Gloghini A, et al. Frequent aberrant promoter hypermethylation of O6-methylguanine-DNA methyltransferase and death-associated protein kinase genes in immunodeficiency- related lymphomas. Br J Haematol. 2003;123:475-478.

70. Gerson SL. MGMT: its role in cancer aetiology and cancer therapeutics. Nat Rev Cancer. 2004;4:296-307.

71. Rinaldi A, Kwee I, Poretti G, et al. Comparative genome-wide profiling of post-transplant lymphoproliferative disorders and diffuse large B-cell lymphomas. Br J Haematol. 2006;134:27-36.

72. Weissmann DJ, Ferry JA, Harris NL, et al. Posttransplantation lymphoproliferative disorders in solid organ recipients are predominantly aggressive tumors of host origin. Am J Clin Pathol. 1995;103:748-755.

73. Zutter MM, Martin PJ, Sale GE, et al. Epstein-Barr virus lymphoproliferation after bone marrow transplantation. Blood. 1988;72:520-529.

74. Armes JE, Angus P, Southey MC, et al. Lymphoproliferative disease of donor origin arising in patients after orthotopic liver transplantation. Cancer. 1994;74: 2436-2441.

75. Chadburn A, Suciu-Foca N, Cesarman E, et al. Post- transplantation lymphoproliferative disorders arising in solid organ transplant recipients are usually of recipient origin. Am J Pathol. 1995;147:1862-1870.

76. Peterson MR, Emery SC, Yung GL, et al. Epstein-Barr virus- associated posttransplantation lymphoproliferative disorder following lung transplantation is more commonly of host origin. Arch Pathol Lab Med. 2006;130:176-180. 77. Harris NL, Swerdlow SH, Frizzera G, Knowles DM. Post-transplant lymphoproliferative disorders. In: Jaffe ES, Harris NL, Stein H, Vardiman JW, eds. Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissue. Lyon, France: IARC Press; 2001:264-269. World Health Organization Classification of Tumours.

78. Shaknovich R, Basso K, Bhagat G, et al. Identification of rare Epstein-Barr virus infected memory B cells and plasma cells in non-monomorphic post-transplant lymphoproliferative disorders and the signature of viral signaling. Haematologica. 2006;91:1313-1320.

79. Vakiani E, Nandula SV, Subramaniyam S, et al. Cytogenetic analysis of B-cell posttransplant lymphoproliferations validates the World Health Organization classification and suggests inclusion of florid follicular hyperplasia as a precursor lesion. Hum Pathol. 2007;38:315-325.

80. Frizzera G, Hanto DW, Gajl-Peczalska KJ, et al. Polymorphic diffuse B-cell hyperplasias and lymphomas in renal transplant recipients. Cancer Res. 1981;41:4262-4279.

81. Chadburn A, Chen JM, Hsu DT, et al. The morphologic and molecular genetic categories of posttransplantation lymphoproliferative disorders are clinically relevant. Cancer. 1998;82:1978-1987.

82. Rea D, Fourcade C, Leblond V, et al. Patterns of Epstein- Barr virus latent and replicative gene expression in Epstein-Barr virus B cell lymphoproliferative disorders after organ transplantation. Transplantation. 1994;58:317-324.

83. Sun X, Peterson LC, Gong Y, et al. Post-transplant plasma cell myeloma and polymorphic lymphoproliferative disorder with monoclonal serum protein occurring in solid organ transplant recipients. Mod Pathol. 2004;17:389-394.

84. Caillard S, Agodoa LY, Bohen EM, Abbott KC. Myeloma, Hodgkin disease, and lymphoid leukemia after renal transplantation: characteristics, risk factors and prognosis. Transplantation. 2006;81:888-895.

85. Dockrell DH, Strickler JG, Paya CV. Epstein-Barr virus- induced T cell lymphoma in solid organ transplant recipients. Clin Infect Dis. 1998;26:180-182.

86. Tsao L, Draoua HY, Mansukhani M, et al. EBV-associated, extranodal NKcell lymphoma, nasal type of the breast, after heart transplantation. Mod Pathol. 2004;17:125-130.

87. Ranganathan S, Webber S, Ahuja S, Jaffe R. Hodgkin-like posttransplant lymphoproliferative disorder in children: does it differ from posttransplant Hodgkin lymphoma? Pediatr Dev Pathol. 2004;7:348-360.

88. Hsi ED, Singleton TP, Swinnen L, et al. Mucosa-associated lymphoid tissuetype lymphomas occurring in post-transplantation patients. Am J Surg Pathol. 2000;24:100-106.

89. Wotherspoon AC, Diss TC, Pan L, et al. Low grade gastric B- cell lymphoma of mucosa associated lymphoid tissue in immunocompromised patients. Histopathology. 1996;28:129-134.

90. Tsao L, Chu KE, Bhagat G, Alobeid B. Development of hairy cell leukemia in a patient after cardiac transplantation. Leuk Lymphoma. 2006;47:361-363.

91. Lones MA, Mishalani S, Shintaku IP, et al. Changes in tonsils and adenoids in children with posttransplant lymphoproliferative disorder: report of three cases with early involvement of Waldeyer’s ring. Hum Pathol. 1995;26:525-530.

92. Fan H, Gulley ML. Epstein-Barr viral load measurement as a marker of EBV-related disease. Mol Diagn. 2001;6:279-289.

93. Rowe DT, Qu L, Reyes J, et al. Use of quantitative competitive PCR to measure Epstein-Barr virus genome load in the peripheral blood of pediatric transplant patients with lymphoproliferative disorders. J Clin Microbiol. 1997;35: 1612- 1615.

94. Green M, Bueno J, Rowe D, et al. Predictive negative value of persistent low Epstein-Barr virus viral load after intestinal transplantation in children. Transplantation. 2000;70:593-596.

95. van Esser JW, Niesters HG, van der Holt B, et al. Prevention of Epstein-Barr virus-lymphoproliferative disease by molecular monitoring and preemptive rituximab in high-risk patients after allogeneic stem cell transplantation. Blood. 2002;99:4364-4369.

96. Gruhn B, Meerbach A, Hafer R, et al. Pre-emptive therapy with rituximab for prevention of Epstein-Barr virus-associated lymphoproliferative disease after hematopoietic stem cell transplantation. Bone MarrowTransplant. 2003;31:1023-1025.

97. Wagner HJ, Cheng YC, Huls MH, et al. Prompt versus preemptive intervention for EBV lymphoproliferative disease. Blood. 2004;103:3979-3981.

98. Greenfield HM, Gharib MI, Turner AJ, et al. The impact of monitoring Epstein-Barr virus PCR in paediatric bone marrow transplant patients: can it successfully predict outcome and guide intervention? Pediatr Blood Cancer. 2006; 47:200-205.

99. Lee TC, Savoldo B, Barshes NR, et al. Use of cytokine polymorphisms and Epstein-Barr virus viral load to predict development of post-transplant lymphoproliferative disorder in paediatric liver transplant recipients. Clin Transplant. 2006;20:389- 393.

100. Chadburn A, Cesarman E, Liu YF, et al. Molecular genetic analysis demonstrates that multiple posttransplantation lymphoproliferative disorders occurring in one anatomic site in a single patient represent distinct primary lymphoid neoplasms. Cancer. 1995;75:2747-2756.

Lawrence Tsao, MD; Eric D. Hsi, MD

Accepted for publication April 12, 2007.

From the Department of Pathology, University of New Mexico, Albuquerque (Dr Tsao); and the Department of Clinical Pathology, Cleveland Clinic, Cleveland, Ohio (Dr Hsi).

The authors have no relevant financial interest in the products or companies described in this article.

Reprints: Eric D. Hsi, MD, Department of Clinical Pathology, Cleveland Clinic, 9500 Euclid Ave, Cleveland, OH 44195 (e-mail: hsie@ ccf.org).

Copyright College of American Pathologists Aug 2007

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