THURSDAY, Jan. 8, 2009 (HealthDay News) -- Hormone therapy may lower a woman's risk of colorectal cancer, especially if she is no longer taking the hormones.
This new finding, published in the January issue of Cancer Epidemiology, Biomarkers and Prevention, further complicates an already murky picture of the risks and benefits of hormone replacement therapy (HRT).
Previous landmark research has shown an increased risk of breast cancer and cardiovascular problems, but a lowered risk of colon cancer. More recent studies have found that the stage in life when a woman takes hormone therapy can influence the effect. The drugs are typically prescribed to women dealing with menopausal symptoms.
Other studies have also found a lowered risk of colon cancer among HRT users and, at this time, the weight of the evidence seems to point in that direction.
"These data do add additional weight to prior reports suggesting that hormone replacement therapy reduces the risk of colorectal cancer," said Dr. Neal Meropol, director of the Gastrointestinal Cancer Program at Fox Chase Cancer Center in Philadelphia.
But the studies have yet to translate into discoveries that can affect medical practice.
"This study highlights the complexity of systems that affect tumor development and growth, and raises the possibility that there will be pathways we can identify that can be specifically targeted that can be used to prevent and treat colon cancer," Meropol added. "These findings open the door to asking other fundamental questions about what causes colon cancers to develop, the results of which could provide clues to new prevention strategies."
The new study, led by researchers at the University of Minnesota School of Public Health, gleaned information on colorectal cancer incidence and hormone use from nearly 57,000 women who had been followed for about 15 years.
The researchers found a 17 percent reduced risk of colorectal cancer among women who had ever used estrogen alone, a 25 percent reduced risk among women currently using estrogen, and a 26 percent reduced risk among those using estrogen for 10 or more years.
Among women taking estrogen plus progestin, there was a 22 percent reduced risk, and a 45 percent reduced risk -- the highest seen -- among those who had stopped taking the combination hormones at least five years earlier.
The researchers also reported a 36 percent drop in risk among women who'd used progestin sequentially -- less than 15 days a month.
It's not clear what the biological mechanisms might be that could contribute to the reduction in risk.
"It appears that estrogens likely have direct or indirect effects on the growth of colonic epithelial cells," Meropol said.
The Women's Health Initiative has more on the health effects of HRT in postmenopausal women.