The long-term use of hormone replacement therapy, which older women abandoned in droves following the news that it may increase the risk of breast cancer, may substantially cut the risk of colorectal cancer, research shows.
The greatest risk reduction — 48 percent — was observed among women who had used a combined estrogen plus progestin hormone regimen for 2 to 5 years, the investigators report in the latest issue of Cancer Epidemiology, Biomarkers and Prevention, published by the American Association for Cancer Research.
"Despite the recent decrease in use of all menopausal hormones, these results suggest an important protective effect of all hormone formulations, especially estrogen plus progestin, for the many women who continue to need and use menopausal hormone therapy," write Dr. Jill R. Johnson at the University of Minnesota, Minneapolis, and colleagues there and at the National Cancer Institute in Bethesda, Maryland.
The current findings stem from a look at data for 56,733 women followed for an average of 15 years, among whom 960 were diagnosed with colorectal cancer. The average age at the first interview conducted from 1979 to 1981 was 55.7 years.
Any use of estrogen therapy was associated with a 17 percent reduced risk in colorectal cancer, the investigators found. Among women who used estrogen, the largest reductions were seen among those who were current users (25 percent reduced risk) and users of 10 or more years duration (26 percent reduced risk).
Risk falls by 22 percent
Johnson and colleagues also found a 22 percent reduced risk of colorectal cancer among those who had ever used estrogen plus progestin in combination. They further found a 36 percent reduction in risk among those who had used progestin sequentially or less than 15 days per month. Past users of estrogen plus progestin, who had stopped at least 5 years ago, had a 45 percent risk reduction.
Although the current study was not designed to look at biological mechanisms for the apparent protective effect of hormone therapy, previous research has suggested that hormones may play a role in decreasing levels of insulin-like growth factors, thereby reducing risk. "The biological mechanism will need to be explored in further studies," Johnson said.
The current findings differ from those reported by members of the Women's Health Initiative, the investigators note, in which estrogen therapy had no effect on rates of colorectal cancer. They attribute the null finding to the shorter duration of treatment and older age of subjects in that study.