The association, which was of borderline statistical significance, suggests that breast cancer in a first-degree relative increases the risk of colorectal cancer by 20%. The risks were higher, however, if more than one relative had breast cancer (OR = 1.7) and if the malignancy was diagnosed when the relative was older than 50 years (OR = 1.4).
Numerous reports have documented the clustering of malignancies in families with hereditary nonpolyposis colorectal cancer and other cancers with highly penetrant genetic mutations, Dr. Ji-Hyun Jang, from the University of Toronto, and co-researchers note. By contrast, data regarding the familial clustering of breast and other hormonal cancers with colorectal cancer in the general population are lacking.
Using data from the Ontario Familial Colorectal Cancer Registry, the research team assessed the occurrence of breast, endometrial, ovarian, and prostate cancer in the first-degree relatives of 1512 subjects with colorectal cancer and in 1953 sex- and age-matched controls.
As with breast cancer, a family history of endometrial or prostate cancer was linked to colorectal cancer. However, on multivariate analysis, the associations were no longer statistically significant.
While familial breast cancer was tied to an increased risk of colorectal cancer, just the opposite was seen with ovarian cancer. Having a first-degree relative with ovarian cancer was tied to a 40% reduced risk of colorectal cancer, although as the researchers point out, the association was not statistically significant.
Further research, the authors emphasize, is important to verify these findings, which “may be of importance to clinicians and genetic counselors advising persons on cancer prevention and screening.”
Int J Cancer 2009;125:918-925.