Many colorectal cancer cases among certain group are hereditary
CLAYTON BOLDT, PH.D.
Hereditary colorectal cancers, caused by inherited gene mutations, are relatively rare for most patients. However, researchers at MD Anderson Cancer Center have discovered a particularly high prevalence of hereditary cancers among those diagnosed with the disease before the age of 35. They suggest that these patients should undergo genetic counseling to determine if their families may be at an elevated risk.
Approximately 5% of all colorectal cancer (CRC) cases are caused by hereditary syndromes such as Lynch syndrome and familial adenomatous polyposis (FAP). Among patients with early-onset CRC, generally defined as a diagnosis before age 50, the incidence of hereditary CRC tends to be higher. However, the prevalence in adolescents and younger adults has not been well characterized.
The current study, published in the Journal of Clinical Oncology, focused on patients diagnosed at age 35 or younger, to better characterize the extent of hereditary CRC in this underrepresented age group.
The research team, led by Eduardo Vilar-Sanchez, M.D., Ph.D., assistant professor of Clinical Cancer Prevention, reviewed data from 193 patients diagnosed with CRC in this age range who underwent genetic counseling at MD Anderson between 2009 and 2013. This study represents the largest reported cohort of CRC patients diagnosed in this age range in the U.S.
“We were very surprised to find that 35 percent of that population of patients had a genetic disease,” says Vilar-Sanchez, “although we hypothesized the proportion would be higher in this age group relative to the general population.”
According to the American Cancer Society, colorectal cancer is the third-most common cancer among men and women in the U.S., with more than 90,000 new cases expected this year. Approximately 90% of those cases will be diagnosed in patients older than 50.
Patients diagnosed with CRC at age 35 or younger account for less than 1.5% of all cases. This population faces unique challenges related to disease aggressiveness, the impact of treatments on fertility and potential genetic risk to family members, explains Vilar-Sanchez.
“Based on our findings, patients under the age of 35 need to be evaluated by a genetic counselor. Period,” says Vilar-Sanchez. “The translation of that information extends well beyond the patient, as there are tremendous benefits from being able to share genetic risk with their parents, siblings and many other family members.”
Genetic findings important for families
In the general population, the risk of being diagnosed with CRC in one’s lifetime is 5%. People with Lynch syndrome, on the other hand, have a lifetime risk of 50-80%. Those with FAP have a 100% chance of developing cancer if no preventive measures are taken.
Genetic testing in family members will identify those with high-risk mutations and allow them to take proper preventive actions, such as behavioral modification to reduce other environmental risk factors. There’s also the potential for them to participate in earlier screening, increased surveillance, prophylactic surgeries and chemoprevention studies, explains Vilar-Sanchez.
Read more about the study on MD Anderson’s website.