Hormone replacement therapy may raise a woman's risk of breast cancer and heart disease but it lowers her risk of colon cancer, according to two studies released on Wednesday.
The studies presented at a meeting of the American Association for Cancer Research further complicate the debate about HRT, used to relieve the effects of menopause including hot flashes and insomnia.
Millions of women stopped taking HRT when a Women's Health Initiative study showed in 2002 that the hormones raised the risk of stroke, heart disease and breast cancer. Hardest hit was Wyeth's Premarin, which is soon to be acquired by Pfizer Inc.
Dr. David Limsui of the Mayo Clinic in Rochester, Minnesota, and colleagues had been studying 41,836 women aged 55 to 69 from Iowa since 1986. They already showed that smoking raises the risk of colon cancer.
Another analysis of the group showed that the women who took HRT lowered their risk of colon cancer, however.
"Women who did use these drugs had a 28 percent lower incidence rate than women who did not use these drugs," Limsui said in a statement.
"But we still don't know how estrogen compounds work in cancer prevention, which is intriguing."
Women who used hormone-based contraceptive pills, for instance, did not have any different risk of colon cancer. "Based on our findings, we need to continue exploring the cancer pathways that might be affected by these hormones," Limsui said.
A second study presented at the same meeting also showed HRT might protect against colon cancer, which is diagnosed in 54,000 U.S. women a year and which kills 25,000 -- making it the third-leading cancer killer of women behind lung cancer and breast cancer.
Katherine Henderson and colleagues at the City of Hope in Duarte, California, and elsewhere studied 62,000 teachers starting in 1995.
Those who ever used HRT had a 27 percent lower risk of colon cancer, they told the meeting.
"Current hormone therapy use, in the form of either estrogen alone therapy or combined estrogen and progestin therapy, lowers colon cancer risk," they wrote.
The effect disappeared among obese women, they added.