DENVER, April 23 (UPI) -- Hormone replacement therapy protected post-menopausal women against colon cancer, researchers at the Mayo Clinic in Rochester, Minn., said.

The study was designed to look at possible links between estrogen exposure and colon cancer molecular subtypes, to determine how these hormones might function as anti-cancer agents, the researchers said.

The study is part of the Iowa Women's Health Study, which enrolled 41,836 women from Iowa, ages 55-69, in 1986. After exclusions, the study group consisted of 37,285 women.

The investigators examined tumor tissue from 553 colorectal cancer patients, specifically looking for associations between self-reported hormone use and a specific DNA methylation pattern, called the CpG island methylator phenotype, or BRAF gene mutations.

No associations were detected between hormone use and these molecular markers. Of note, the investigative team previously reported that certain environmental exposures, such as cigarette smoking, might increase colorectal cancer risk through DNA methylation pathways.

"In our large, prospective study, use of hormone therapy seemed to be beneficial with respect to reducing colorectal cancer risk -- women who did use these drugs had a 28 percent lower incidence rate than women who did not use these drugs," lead author Dr. David Limsui in a statement. "But we still don't know how estrogen compounds work in cancer prevention, which is intriguing."

The finding was presented at the American Association for Cancer Research's 100th annual meeting in Denver.

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