Raloxifene and colorectal cancer.

OBJECTIVE

To determine the effect of raloxifene on colorectal cancer (CRC) risk.

METHODS

We analyzed data from the Multiple Outcomes of Raloxifene Evaluation (MORE) trial, a randomized, blinded clinical trial designed to determine the effect of raloxifene on vertebral fracture risk. In this trial, 7705 women received either raloxifene or placebo and were followed for an average of 3.4 years. CRC cases were classified as definite (pathology available), probable (imaging or colonoscopic diagnosis), or possible (self-report). Relative hazard for CRC was calculated using multivariate Cox proportional hazards models.

RESULTS

Fifty cases of definite or probable CRC were diagnosed; 40 were definite and 10 probable. Twenty-nine cases occurred among the 5129 women in the raloxifene group, and 21 occurred among the 2576 women in the placebo group (p = 0.15). The relative hazard for CRC for women treated with raloxifene was 0.78 (95% CI 0.43, 1.43, p = 0.43). Restricting the analysis to definite CRC, the relative hazard was 0.77 (95% CI 0.39, 1.5, p = 0.45).

CONCLUSIONS

Although the MORE trial was large, the number of CRC cases was too small to provide definitive evidence concerning the effect of raloxifene on CRC risk. There does not appear to be a substantial increased risk of CRC with raloxifene use. Studies including larger numbers of women and women at risk for CRC should further investigate the effect of raloxifene on CRC.