No evidence for variation in colorectal cancer risk associated with different types of postmenopausal hormone therapy.

Little is known about the effects of various types, modes, and routes of hormone replacement therapy (HRT) on the risk of colorectal cancer (CRC) among postmenopausal women. We conducted a population-based case-control study with validation of self-reported hormone use and no upper age limit. In 1,456 postmenopausal women aged 45-94 years (546 cases, 910 controls), the use of HRT was associated with reduction in CRC risk among ever users (adjusted odds ratio (OR) 0.65, 95% confidence interval 0.50-0.84), current users, and recent users. There was no evidence that risk reduction among current users varies by age. Risk reduction was seen both in estrogen-only therapy (0.42, 0.23-0.78) and in combination therapy (0.60, 0.41-0.87), the latter regardless of the mode of therapy, whether with hormone patches (0.40, 0.17-0.90) or with oral tablets (0.59, 0.39-0.90). In combination with estrogen, progestagens of the norethisterone and levonorgestrel families were associated with strong reduction in CRC risk.