Postmenopausal women who take an estrogen-only hormone replacement therapy do not increase their risk of developing breast cancer if they take hormones for fewer than 10 years but increase their risk by 42% if they take hormones for more than 20 years, according to a study published in the May 8 edition of the journal Archives of Internal Medicine, the AP/Yahoo! News reports (Burghart, AP/Yahoo! News, 5/8). Wendy Chen, an oncologist and epidemiologist at Brigham and Woman's Hospital and the Dana-Farber Cancer Institute in Boston, and colleagues beginning in 1980 observed 11,508 postmenopausal women enrolled in the Nurses Health Study who had hysterectomies and reported use of estrogen-only HRT. Researchers every two years added more women who met those qualifications to the cohort and by 2000, 28,835 women were included in the study. Researchers performed a follow-up that ended in 2002 (Chen et al., Archives of Internal Medicine, 5/8). During the study, 934 of the women, or about 3.2%, developed breast cancer, 708 of whom had taken estrogen-only HRT and 226 of whom had never used HRT, BBC News reports (BBC News, 5/8).

Findings
The study finds that breast cancer risk decreased about 10% in the first 10 years of estrogen-only HRT use and increased slightly during the next 10 years as compared with women not taking HRT, but neither finding was statistically significant (Parker-Pope, Wall Street Journal, 5/9). Breast cancer risk increased by a statistically significant 42% for women who took HRT for more than 20 years. In addition, the risk of hormone-responsive breast cancer, the most common form of the cancer in the U.S., increased by 48% for women who took HRT for at least 15 years (McVicar, South Florida Sun-Sentinel, 5/9). The study also finds that thinner women taking estrogen HRT for more than 20 years had a 77% higher risk of developing breast cancer than thinner women who did not take HRT, while overweight women had a 25% increased risk of breast cancer after 20 years of HRT compared to overweight women not taking hormones. According to the Journal, about 3.5 million of the 4.4 million U.S. women currently taking HRT are taking the estrogen-only form (Wall Street Journal, 5/9). "This says at least for the shorter-term [estrogen HRT] users, you don't need to panic," Chen said, adding that longer-term users should consider if alternatives are available and the reasons for the longer use (AP/Yahoo! News, 5/8).

NPR's "Morning Edition" on Tuesday reported on the study. The segment includes comments from Chen; Gail Greendale, a professor of medicine at the David Geffen School of Medicine at the University of California-Los Angeles; and JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital (Aubrey, "Morning Edition," NPR, 5/9). The complete segment is available online in RealPlayer.