NEW YORK (Reuters Health) - 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).
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.
SOURCE: Cancer Epidemiology, Biomarkers and Prevention, January 2009.
