November 5, 2008

First Cancer Patient Genome Completed

For the first time, scientists have decoded the entire genome of a cancer patient, identifying a series of genes never before linked to the type of white blood cell cancer that ultimately ended the patient's life.

Researchers at Washington University School of Medicine in St. Louis said the study represents a new approach to grasp the genetic underpinning of cancer and pave the way for better treatments.

Dr. Timothy Ley, who led the study, said the patient was a woman in her 50s who died 23 months after she was diagnosed with acute myeloid leukemia. Cancer experts said only one in five patients who get this disease, also called AML or acute myelogenous leukemia, live more than five years after diagnosis.

In an effort to find genetic mutations that might initiate the development of AML, the researchers sequenced the genes in a sample of normal skin tissue from the woman as well as the genes in her tumor cells taken from bone marrow through a technique called high-throughput sequencing.

The team was able to pinpoint 10 mutated genes in the cancerous tissue apparently involved in triggering AML by comparing tumor tissue to normal tissue.

Prior research had linked two of them to AML.

"The other eight were all things that caught us off guard. They're all new. And they are all in genes that we didn't really have on our radar for this particular kind of cancer. In retrospect, they all make sense," Ley said.

The researchers said three of them normally act to suppress tumor growth, four are involved in promoting cell growth and the final one may affect how drugs enter a cell.

"This is the only way we would have found these mutations. There's no other path to get this information. I think it really has begun to tell us how little we know about cancer," Ley said.

Ley and colleagues said treatment of AML had shown little change in the past two decades because most of the genetic events behind the disease had remained unknown.

"This is the first human cancer genome that's been sequenced. In the past, we've always looked at parts of the genome for mutations. But this is the first time that we've been able to look at everything," Ley said.

Cheaper and faster DNA sequencing technology can now offer scientists a deeper genetic understanding of cancer and can serve as the foundation for developing more effective ways to diagnose and treat cancer, the researchers said.

"There are probably many, many ways to mutate a small number of genes to get the same result, and we're only looking at the tip of the iceberg in terms of identifying the combinations of genetic mutations that can lead to AML," said Richard Wilson, one of the researchers.

AML is a cancer of blood-forming cells in the bone marrow that arises from mutations that accumulate in people's DNA over the course of their lives. Currently, doctors know very little about the precise nature of those changes and how they disrupt biological pathways to cause the uncontrolled cell growth that is the hallmark of cancer.

According to the American Cancer Society, an estimated 13,000 cases of AML will be diagnosed in the United States this year, and some 8,800 will die of the disease.

The full study was published in the journal Nature.


Image Caption: Acute myelogenous leukemia cells. Courtesy Washington  School of Medicine


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