People with BRCA mutations, including those with a family history of breast cancer, have a risk for colorectal cancer that is roughly the same as that of the general population, according to an article in the January 7th issue of the Journal of the National Cancer Institute.

“People carrying BRCA1 or BRCA2 mutations already have their plates full managing a high risk of breast and ovarian cancer,” said lead investigator Stephen B. Gruber, MD, PhD. “The good news in our study is that they don’t have to deal with an increased risk of colorectal cancer, as well.”

Previous research to determine whether BRCA mutations increase the risk of colorectal cancer has produced mixed and inconsistent results. In the current study, the international group tested blood samples from 1,422 patients with colorectal cancer and samples from 1,566 control subjects without colorectal cancer for mutations in the genes BRCA1 and BRCA2.

Study participants were selected from a population-based epidemiology study on colorectal cancer in Israel, and cancer patients were matched with adults without colorectal cancer who were of the same age, sex, and ethnicity, and lived in the same geographic area. The DNA assays were designed to identify 3 specific mutations in BRCA1 or BRCA2 (founder mutations) that are present in about 2.5 percent of men and women of Ashkenazi Jewish ancestry. Of the patients with colorectal cancer in the study, 1,002 (70.5 percent) were Ashkenazi Jews, as were 1,038 people (66.3 percent) without colorectal cancer.

“The advantage of working with founder mutations is that we know exactly where they occur in the DNA sequence, so it makes it makes it relatively easy to develop an assay to identify them,” explained Bethany L. Niell, a graduate student and lead author of the study.

When they analyzed the results of DNA testing, scientists found no statistically significant difference between the number of cancer patients with BRCA1 or BRCA2 mutations (24), and the number of non-cancer controls whose DNA contained 1 of these mutations (20). “We found no strong common genetic basis between colorectal and breast cancer,” said Gruber. “They are different diseases with different genetic factors.”

In the second part of the study, scientists compared whether a family history of breast cancer in a parent, sister, or daughter was associated with the development of colorectal cancer. Gruber said, “We found no association between a family history of breast cancer in a first-degree female relative and an increased risk of colorectal cancer.”

“Population-based studies like the [Israeli] study allow you to select patients and controls from the same general population,” explained Niell. “Previous studies may have overestimated the risk of colorectal cancer because they used patients from high-risk families - those with a family history of breast or ovarian cancer - who may not be representative of the entire population.”

Although current U.S. clinical care guidelines recommend informing people with a mutation in BRCA1 or BRCA2 of an increased risk of colorectal cancer, Gruber concluded that physicians should advise people with these mutations to follow colorectal cancer screening guidelines established for the general public: “Anyone over age 50 is at risk for colorectal cancer and screening save lives.”