Colorectal cancer after breast cancer: a case-control study

The risk of colorectal cancer (CRC) after BC and the additional risk factor of tamoxifen exposure were investigated by several studies with conflicting results. We performed a case-control study aimed at investigating if a past history of breast cancer is a risk factor of developing adenomas or CRC and establishing whether tamoxifen exposure is an additional risk factor.

We enrolled 175 asymptomatic women with a past history of BC and invited them to undergo a screening colonoscopy. In the same period, we enrolled 201 healthy asymptomatic women (HG) with no family history of CRC which were referred to our Unit for a colonoscopy.

Mean age at colonoscopy was 56.9 years for BC patients vs. 56.3 years for HG (p=0.58). In 32/175 (18.3%) BC patients, 38 lesions and in 17/201 (8.4%) controls, 20 lesions (p=0.029) were diagnosed. BC patients had 5/32 CRC vs. no CRC in the HG. Multivariate analysis of age, family history of CRC, timing from BC diagnosis and first colonoscopy, tamoxifen treatment revealed that none of the variables were predictive of the presence or absence of adenomas or CRC in the BC group.

In the present study BC group had a significant higher prevalence of adenoma or CRC than controls. Tamoxifen exposure did not increase the risk of adenoma or CRC. Our data support the hypothesis that BC is a risk condition for adenomas or CRC. The risk is small but present and a screening colonoscopy should be offered to these patients.