Estrogen replacement therapy and colorectal cancer risk in elderly women.

PURPOSE: Colorectal cancer is the fourth most common incident cancer in the United States and causes more cancer deaths than any site except lung. Twenty-two epidemiologic studies have examined the relationship of estrogen replacement therapy and colon and rectal cancers with inconsistent results. However, recent studies suggest a reduced risk among current users. The purpose of the present study was to analyze the Leisure World Cohort for possible association of estrogen replacement therapy with colorectal cancer risk.
METHODS: A cohort of 7,701 female members who were initially free of cancer and self-reported their use of estrogen replacement therapy were followed up from June 1981 through December 1995 for development of colorectal cancer.
RESULTS: We observed 249 incident colorectal cancer cases and 89 colorectal cancer deaths. Women who had used estrogen replacement therapy had an age-adjusted colorectal cancer incidence rate of 2.67 per 1,000 person-years compared with 3.30 per 1,000 person-years among lifetime nonusers (relative risk = 0.81; 95 percent confidence interval, 0.63 to 1.04). Among recent users the incidence was one-third lower than among lifetime nonusers (relative risk = 0.66; 95 percent confidence interval, 0.44 to 0.98). Risk did not differ by duration of estrogen replacement therapy, usual dose of conjugated estrogen, or route of estrogen administration. The effects of current estrogen replacement therapy on colon cancer incidence (relative risk = 0.70; 95 percent confidence interval, 0.45 to 1.09), right-sided colon cancer incidence (relative risk = 0.75, 95 percent confidence interval, 0.38 to 1.48), left-sided colon cancer incidence (relative risk = 0.76; 95 percent confidence interval, 0.41 to 1.41), rectal cancer incidence (relative risk = 0.52; 95 percent confidence interval, 0.21 to 1.31), and colorectal cancer mortality (relative risk = 0.82; 95 percent confidence interval, 0.44 to 1.54) were similar.
CONCLUSION: A reduced risk of colorectal cancer may be an additional benefit of recent estrogen replacement therapy use, which should be considered by postmenopausal women when deciding whether to use hormones.