Test All Colon Cancers For Inherited Form
One in 35 people with colon cancer carry a hereditary form of the disease, according to the second of two studies led by researchers at The Ohio State University Comprehensive Cancer Center.
Based on the finding, researchers recommend screening all colon-cancer patients for Lynch syndrome, the most common inherited form of colon cancer.
The studies involved 1,566 colon-cancer patients who were tested for mutations in one of the four genes responsible for the condition. Lynch syndrome gene mutations were found in 44 patients, and each of these had an average of three family members who also had inherited one of the mutations but had not yet developed cancer.
In addition, about half the patients were over age 50, and a quarter lacked a family history of the disease. Typically, genetic counseling and testing for hereditary colon cancer is done only in those with a family history of the disease or who develop it before age 50. Results were published in a recent issue of the Journal of Clinical Oncology.
"People with a Lynch syndrome gene mutation have an almost 100 percent lifetime risk of cancer," says study leader Dr. Albert de la Chapelle, professor of Molecular Virology, Immunology and Medical Genetics.
"We recommend that all newly diagnosed colorectal cancer patients be routinely screened for Lynch syndrome."
The second study also showed that hospitals can use a commonly available test to identify colon cancer patients with the syndrome.
People who inherit a Lynch syndrome mutation have a high risk for colon and uterine cancer, and an increased risk for several other cancers, de la Chapelle says. First-degree relatives of those affected have a 50 percent chance of carrying the same mutation.
"We were surprised by the number of patients we identified with Lynch syndrome who were diagnosed over age 50 and who did not meet any of the accepted family history criteria," says first author Heather Hampel, a certified genetics counselor with Ohio State's clinical cancer genetics program.
"These cases would be missed altogether unless all newly diagnosed colon cancer patients are screened for Lynch syndrome," she says. Furthermore, people with Lynch syndrome related colon cancer generally have a better prognosis, and new research suggests that they often respond better to certain therapies.
"The fact that one in 35 colorectal cancer patients has Lynch syndrome is staggering, and when you consider the implications for other family members, it could be considered a significant public health issue."
Healthy people with Lynch syndrome mutations need closer cancer surveillance, with annual colonoscopies starting at age 25, de la Chapelle says, to prevent cancer and death from cancer.
It is also important to identify those high-risk family members who lack the mutation, he says, because those relatives do not require intense cancer surveillance.
The first of the two studies was published in the New England Journal of Medicine in 2005 and involved 1,066 colorectal cancer patients who were tested for microsatellite instability (MSI), a hallmark of Lynch syndrome. A few cases were also tested using a more recently refined technique called immunohistochemistry (IHC).
The second study examined an additional 500 patients using both the MSI and IHC tests in a head-to-head comparison. Eighteen of the patients had Lynch syndrome.
Both groups together yielded 44 cases of Lynch syndrome, for a prevalence of 2.8 percent, or one case per 35 colorectal cancer patients.
The two tests performed equally well, but IHC is recommended because it is easier, is available in most hospitals, and it reveals which gene is affected.