May 14, 2009 -- A test that characterizes each tumor by its genetic signature may soon help some colon cancer patients decide whether to have chemotherapy after surgery or whether they can safely forgo additional treatment.
"This test empowers doctors and their patients to make more informed decisions about chemotherapy after surgery," says researcher David Kerr, MD, professor of cancer medicine at the University of Oxford.
If its name sounds familiar, that's because the new test is a version of the Oncotype DX breast cancer test that is already being used to guide the treatment of estrogen-fueled breast cancers that have not spread to the lymph nodes.
The version for colon cancer patients is expected to be available next year, according to Genomic Health, which makes both tests and funded the work.
Kerr discussed a new study on the colon cancer test at a news conference sponsored by the American Society of Clinical Oncology (ASCO).
Risk of Cancer Recurrence
About 25%-30% of people diagnosed with colon cancer have stage II disease. That means the cancer has spread through the wall of the colon and may have spread to nearby tissues or organs, but has not spread to the nearby lymph nodes or distant areas.
Although most people with stage II colon cancer are cured after surgery alone, about 20%-25% experience a recurrence of cancer.
The problem: "There's no good tool to tell us who will have a recurrence after surgery and who won't," says ASCO President Richard L. Schilsky, MD, professor of medicine at the University of Chicago. He was not involved with the work.
That's where the new test, which looks at the activity of a dozen genes involved in colon cancer risk, comes in.
For the study, the researchers analyzed 761 genes from 1,851 patients with stage II colon cancer and identified 12 genes with the potential to predict the likelihood of cancer recurrence.
Then, they analyzed tissue samples collected from 711 people who had undergone surgery for stage II colon cancer.
Depending on the activity of the 12 genes, participants were assigned a recurrence score and classified as being at low, medium, or high risk of recurrence.
The study showed that the recurrence score accurately predicted the risk of cancer coming back, Kerr says.
People in the low-risk category had only about a 12% chance of having a recurrence at three years, the study showed. But people who fell into the high-risk category had a 22% chance of having recurrence.
The Chemotherapy Dilemma
The recurrence score can be used to guide the difficult decision of whether to have chemotherapy after surgery, Kerr tells WebMD.
In patients with low recurrence scores, "I don't think any doctor would recommend chemotherapy. The side effects and hassle of chemotherapy outweigh the benefits," he says.
But in patients with high recurrence scores, chemo can cut the risk of cancer coming back by another 5%, Kerr tells WebMD. "We know from other work that patients are willing to accept side effects given that degree of benefit."
What about patients at intermediate risk? There, the answer is less clear, Kerr says. "In my clinical practice, I find that younger medium-risk patients tend to say the benefits of chemo outweigh the risks. Those age 70 and older say, 'Thanks, but no thanks.'"
Schilsky tells WebMD that the new test is a good step forward. But he says he would like to see it better discriminate between patients at low and high risk of recurrence.
Kerr says studies to refine the test, incorporating more genes that may be involved in colon cancer and following larger numbers of patients, are under way.
His team also hopes to develop a score to predict not only whether a patient will suffer a recurrence, but also whether chemotherapy will actually work. Their first attempt at such a test failed, largely due to too few patients, Kerr says.