Following the 2002 report from the Women’s Health Initiative (WHI) clinical trial, the use of hormone replacement therapy dropped from about 40% of eligible women to about 20%. The decreased usage was due to the WHI finding that HRT was accompanied by an elevated risk for breast cancer. However, that left about 30 million women in the U.S. using HRT. In a report published online August 10 in Cancer Epidemiology, Biomarkers & Prevention, Tanmai Saxena, an MD/PhD student at the Keck School of Medicine at the University of Southern California, in Los Angeles, and colleagues found that women who used estrogen for more than 15 years had a 19% greater risk of developing breast cancer than women who had never been on HRT. In addition, the authors also found that breast cancer risk was higher for women who took postmenopausal hormones for longer periods and highest for those using combined estrogen plus progestin therapy (EPT). Current use of either estrogen therapy (ET) or EPT was associated with higher risk than past use of the same regimen, and risk increased with the number of days per month of progestin in a current EPT regimen. Of interest, the results suggest that there is also an increased risk for tumors that are HER2-positive. HER2-positive breast cancer is a breast cancer that tests positive for a protein called human epidermal growth factor receptor 2 (HER2), which promotes the growth of cancer cells. In about one of every five breast cancers, the cancer cells make an excess of HER2 due to a gene mutation. This gene mutation and the elevated levels of HER2 that it causes can occur in many types of cancer in addition to breast cancer.
The USC researchers used the California Teachers Study cohort to evaluate the effects of ERT on the risk for breast cancer. Details of the study:
• Participants in this study completed baseline health surveys in 1995. The current analysis focused on women without a history of breast cancer who were perimenopausal or postmenopausal and were younger than 80 years.
• Breast cancer cases were identified through a state cancer registry.
• A total of 56,867 women were included in the study analysis, and 2857 (5%) of these women were diagnosed with invasive breast cancer through 2006. The mean age at the time of diagnosis among women with breast cancer was 67.1 years.
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