A prospective study of universal genetic testing suggested that one in six colorectal cancer patients have an inherited genetic predisposition to the cancer. More than half of the patients with genetic mutations identified in this study would have been missed if the patients had undergone genetic testing based on current practice. In 11% of patients, the genetic findings led to a change in treatment, including the type of surgery or targeted cancer therapy.
These results were presented at the American College of Medical Genetics and Genomics annual meeting and published in Clinical Gastroenterology and Hepatology.
“This study shows the limitations of relying on current clinical practice guidelines for genetic evaluation, which prioritize age of cancer diagnosis and family cancer history,” said investigator Niloy Jewel Samadder, MD, of the Mayo Clinic in Phoenix.
“We were surprised that more than 50% of the patients with a genetic mutation would not have been identified had we relied on national practice guidelines or only used a small colon cancer-specific gene panel, as is commonly employed in clinical practice. The fact that more than 10% of patients actually had changes in the type of surgery or chemo/immunotherapy they received gives the strongest indicator of how genetics can revolutionize and individualize cancer care,” Dr. Samadder said.
He added that identifying a germline predisposition has multiple values, including understanding the reason patients and their family members develop specific cancers, preventing the development of new cancers in patients and family members by providing targeted prevention and screening for those at genetic risk, and improving survival in patients with a genetic driver of cancer via targeted therapy.
Study details
The researchers used a next-generation sequencing platform with more than 80 genes in colorectal cancer patients (not selected for age or family history) receiving care at Mayo Clinic Cancer Centers between April 1, 2018, and March 31, 2020.
The study included 361 patients with a median age of 57 years. Pathogenic germline variants were identified in 56 patients (15.5%), including 44 patients with moderate and high penetrance cancer susceptibility genes.
Younger age (under 50 years old) was associated with having a germline mutation, but “more importantly, gender, family cancer history, and stage of cancer were not,” Dr. Samadder said.
“The current clinical guidelines rely heavily on these characteristics to determine who should and should not be referred for genetic testing,” he continued. “Our study suggests that even older patients with colorectal cancer have a high rate of having pathogenic germline mutations [12%], so restricting genetic testing to only those under age 50 will miss a substantial portion of patients who might benefit from this test.”
Genetic testing for all
“Our findings support the broad use of genetic testing in all colorectal cancer patients, regardless of age, gender, ethnicity, family cancer history, or stage of cancer,” Dr. Samadder said.
“This study adds to a growing body of literature that provides evidence that cancer susceptibility due to variants in single genes is more common than previously appreciated,” said Marc S. Williams, MD, president of the American College of Medical Genetics and Genomics. “Current testing guidelines seem to be relatively insensitive and miss opportunities for testing of patients.”
Dr. Williams noted that 11% of patients in this study had a change in disease management related to a genetic testing result, which is “a relatively modest impact.”
“Another potential advantage of [universal] testing was the opportunity to test at-risk relatives,” Dr. Williams added. “However, only 16% of eligible individuals pursued testing. This is consistent with other studies and represents an opportunity for testing new ways to improve uptake of cascade screening.”
Dr. Williams said rigorous prospective studies enrolling large numbers of patients from diverse backgrounds are needed to inform the development and updating of genetic testing guidelines.
He disclosed no conflicts of interest. Dr. Samadder disclosed relationships with Janssen Research and Development, Recursion Pharmaceuticals, and Cancer Prevention Pharmaceuticals. The research was funded by the Mayo Clinic, Desert Mountain Members’ CARE Foundation, David and Twila Woods Foundation, and the Gerstner Foundation.