Increased risk of breast cancer in first-degree relatives of Crohn's disease patients. An IG-IBD study

Increased rates of colorectal cancer have been reported in patients with ulcerative colitis as well as with Crohn's colitis. This risk could be the result of shared genetic susceptibility and could be co-inherited rather than being just secondary to a long-standing, extensive mucosal inflammation.

To assess the prevalence of all malignancies in first-degree relatives of Crohn's disease patients in order to establish whether any association exists.

A total of 632 outpatients with a diagnosis of Crohn's disease and 632 control subjects were recruited. Information concerning the presence of malignancies was collected in 3,292 first-degree relatives of Crohn's disease patients and in 3,303 first-degree relatives of controls.

Two hundred and fourteen (6.5%) subjects were found to be affected by malignancy in the first-degree relatives of Crohn's disease patients and 180 (5.5%) in the first-degree relatives of controls. Forty-seven (7.4%) of Crohn's disease patients had a first-degree relative with IBD, but none of them had cancer. The frequency of extra-intestinal malignancies was higher in first-degree relatives of Crohn's disease patients than in those of controls (p=0.011). Frequency of breast cancer in female relatives of Crohn's disease patients, mainly in mothers, was two-fold higher than that in controls (0.91% versus 0.42%; odds ratio=2.16; 95% confidence interval=1.14-4.08; p=0.015). The presence of breast cancer showed no association with any specific phenotype of disease in Crohn's patients.

These results did not corroborate the hypothesis about a common genetic susceptibility between Crohn's disease and colorectal cancer. An unexpected finding was the more frequent occurrence of extra-digestive malignancies. The prevalence of breast cancer in first-degree relatives of Crohn's disease patients, in particular the mothers, was more than double than in those of controls. This association, if confirmed, would suggest that there may exist common genetic and/or environmental factors for Crohn's disease and breast cancer.