June 23, 2005
Vaginal Cancer Detected More Often with PET Than CT Scans
In patients with vaginal cancer, PET scans detected twice as many primary tumors and cancerous lymph nodes as did CT scans, according to researchers at Washington University School of Medicine in St. Louis. At this time, however, Medicaid, Medicare and many private insurers specify CT (computed tomography) for diagnosing and monitoring this cancer.
The researchers hoping to encourage a change in that standard report their comparison of the two methods in the July 1 issue of the International Journal of Radiation Oncology, Biology, Physics.Like cervical cancer, vaginal cancer advances predictably, spreading to lymph nodes increasingly higher up in the body as the disease progresses. Doctors use information about the size of the tumor and the involvement of lymph nodes to determine treatment, such as where to target radiation and whether to use surgery or chemotherapy.
The results of this study suggest that the use of PET, or positron emission tomography, would make diagnosis of vaginal cancer much more accurate and allow better selection of treatment, according to study author Perry W. Grigsby, M.D., professor of radiation oncology and radiology.
However, until the procedure is reviewed and approved by the Centers for Medicaid and Medicare Services (CMS), vaginal cancer patients will most likely not be evaluated using PET scans.
CMS policies set standards often followed by private health insurance companies and therefore strongly determine what procedures physicians use. Studies such as this one play an essential role in CMS acceptance of new procedures.
"In 1999, we began publishing papers showing that PET scans picked up more cancerous lymph nodes in patients with cervical cancer," Grigsby says. "Armed with data from these kinds of studies, I went to Washington in 2003 to petition CMS to approve the use of PET scans for diagnosis of cervical cancer. In January of 2005, the procedure was approved for cervical cancer."
Several other cancers, in addition to cervical cancer, can be diagnosed and monitored using PET scans as the result of CMS acceptance. Grigsby is now working to persuade CMS that PET scans will improve the diagnosis and treatment of vaginal cancer.
"CT scans are useful in many cases, but they have a limit to their resolution," says Grigsby, who sees patients at the Siteman Cancer Center and is affiliated with Barnes-Jewish and St. Louis Children's Hospitals. "When you're evaluating lymph nodes for cancer using CT, the node has to be at least a centimeter for it to be considered abnormal. But PET scans can detect much smaller nodes that have cancerous cells."
PET scans are effective for this purpose because they use a different detection method than CT scans. CT scans obtain cross-sectional views of the body by detecting the amount of X-rays that pass through the body's tissues. Small tumors can easily escape detection.
On the other hand, PET scans detect radioactivity that emanates directly from a tumor after a patient has received a dose of radioactive glucose, which accumulates in tumors. Even tiny tumors will collect enough "hot" glucose to show up on the PET scan.
Vaginal cancer is very similar to cervical cancer; both are linked to the presence of human papillomavirus. About 1 percent of gynecological malignancies are vaginal. The rates of survival with vaginal cancer are considered to be similar to those of cervical cancer.
According to Grigsby, if cervical cancer has not spread beyond its primary site, about 90 percent of patients will survive. The rate of survival drops to 70 percent if the cancer has spread to lymph nodes in the pelvis. The next stage of progression, in which the cancer has spread to nodes near the heart, has a survival rate of 30 to 40 percent. After that, untreated cervical cancer will move to nodes near the collar bone and will not be survivable.
"It is very important to know at the time of diagnosis, for both cervical and vaginal cancer, not only what the patient has in the pelvis, but where the tumor has spread," Grigsby says. "That will absolutely determine the kind of treatment."
On the World Wide Web: