Gene Screen May Predict Colon Cancer's Return
THURSDAY May 14, 2009 -- The first genomic test aimed at predicting colon cancer recurrence may help individualize treatment for patients, leading to less toxic and more targeted therapy choices, scientists say.
The Oncotype DX test differentiated which patients with stage II colon cancer were more likely to have a recurrence and which were not. According to the research team, those with lower odds of recurrence might be able to forgo sometimes toxic and costly chemotherapy and stick to surgery alone.
The study is to be presented at the American Society of Clinical Oncology (ASCO) annual meeting, which starts later this month in Florida. The U.K. researchers described their findings Thursday in a special ASCO preview news conference.
The new gene test was not able to show whether or not chemotherapy would actually benefit the higher-risk group, the researchers said.
Still, "we think this will be a clinically useful tool when coming to select which patients will receive chemotherapy," said study lead author Dr. David Kerr, a professor of cancer medicine at the University of Oxford.
The test is very similar to the Oncotype DX test that is already available to stratify breast cancer patients by risk, added Dr. Richard L. Schilsky, president of ASCO and professor of medicine at the University of Chicago. In fact, the new colon cancer test will likely be commercialized by the same company that markets the breast cancer test, Genomic Health, he predicted. That company funded the new study.
The study authors believe the new test, which is not quite as strong a predictor as the existing breast cancer test, will be available for use in hospitals by 2010.
"One of the major challenges facing us as oncologists is selecting the right patients for the right drugs at the right time. That's what this study is all about," Kerr said.
Most individuals diagnosed with relatively early, stage II colon cancer (representing 25 to 30 percent of all cases) can be cured with surgery alone. A small minority benefit from added chemo.
But, Kerr said, "there's no clear consensus on how to select patients" who might gain from this additional chemotherapy, and weed out those who would not.
The research team started out by analyzing almost 800 genes from almost 1,900 colon cancer patients. They then tested an initial, promising gene signature in about 1,500 patients. Half of these individuals received chemo and half did not.
The presence of certain genes was able to predict those with a higher risk of recurrence and those with a lower risk, the team found.
"A seven-gene signature for the first time ever gives a significant prognostic recurrence score," Kerr said. "This allows us to define a population of patients at low risk of recurrence -- about a 10 percent chance of the cancer coming back [in three years] -- in whom I would counsel that chemotherapy would be of very little value indeed."
For the other group, recurrence rates closer to 20 or 25 percent at three years may indicate a benefit to getting chemo, he said.
Doctors already look at "T-stage" of a tumor (is it locally advanced?, etc.) as well as "mismatch repair," which refers to a gene repair mechanism, to predict recurrence. However, according to Kerr, a large group of patients would benefit from this new tool that would not benefit from the two older screens.
"The new tool is an independent important variable," Kerr said. "There would be 70 percent of patients in whom T-stage and mismatch will not be informative and we think that, in this group, the new tool will provide a useful addendum to the clinical decision-making process."
There's more on colorectal cancer at the U.S. National Cancer Institute.
Posted: May 2009