Colorectal cancer and HRT

Of the 19 trials investigating the effect of HRT on the risk of colorectal cancer 15 show a beneficial effect.

The benefits are most marked amongst long term users:

• 5-10 years of HRT probably halves the risk of colorectal cancer
• the benefits of risk reduction for colorectal cancer were shown in the Women's Health Initiative study. In this study there was a relative risk of 0.63 at 5.2 years for the development of colorectal cancer (comparing oestrogen plus progestogen arm vs. placebo group) (2) - this meant an reduced absolute risk of 6 per 10,000 women per year

Note though that more recent evidence, concerning use of conjugated equine oestrogen in women who have had a hysterectomy, did not show an increase in breast cancer, thromboembolic disease, colorectal cancer or heart disease in 6.8 years of use (3).

• this study did however reveal an increased risk of stroke and decreased risk of hip fracture in women taking conjugated equine oestrogen during the 6.8 year period

A review states that (4):

• there is evidence that postmenopausal oestrogen plus progesterone hormone use decreases the incidence of colorectal tumour but a non-comparable benefit was demonstrated for oestrogen alone

Reference:

1. Boyle P, Langman JS (2000). Epidemiology in "ABC of colorectal cancer". BMJ, 321, 805-8.
2. Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. Principal results for the Women's Health Initiative Randomized controlled trial. JAMA 2002; 288:321-333
3. Anderson GL et al (2004). Effects of conjugated equine estrogen in postmenopausal women with hysterectomy: the Women's Health Initiative randomized controlled trial. JAMA;291:170-12.
4. Labianca R et al. Primary colon cancer: ESMO Clinical Practice Guidelines for diagnosis, adjuvant treatment and follow-up. Ann Oncol. 2010;21 Suppl 5:v70-7.