Hormone therapy and colorectal cancer

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The combination of estrogen plus progestin, which women stopped taking in droves following the news that it may increase their risk of breast cancer, may decrease their risk of colorectal cancer, as per a report reported in the recent issue of Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research.

"In comparison to women who had never taken these hormones, the use of estrogen plus progestin was linked to a reduced risk of colorectal cancer," said Jill R. Johnson, M.P.H., a doctoral student at the University of Minnesota School of Public Health.

The largest risk reduction, approximately 45 percent, was seen among women who had completed use of estrogen plus progestin five or more years previously.

Johnson and her colleagues extracted data from 56,733 postmenopausal women who participated in the Breast Cancer Detection Demonstration Project follow-up study. Hormone treatment use and other risk factors were ascertained through telephone interviews and mailed questionnaires between 1979 and 1998. During an average 15 years of follow-up, Johnson and his colleagues identified 960 new cases of colorectal cancer in this population.

Any use of estrogen treatment was linked to a 17 percent reduced risk in colorectal cancer. Among those who used estrogen, the largest reductions were seen among those who were current users (25 percent reduced risk) and users of ten or more years duration (26 percent reduced risk).

Scientists also found a 22 percent reduced risk 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 five years ago, had a 45 percent risk reduction.

Eventhough Johnson's study was not designed to look at biological mechanisms for the protective effect of estrogen treatment, she did say that prior 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," said Johnson.


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