On May 31, 2002, the Women’s Health Initiative (WHI) randomized trial of hormone therapy (HT) was stopped early because the risks of HT were found to outweigh the benefits. Women randomized to estrogen plus progestin therapy (EPT) experienced an excess risk of invasive breast cancer, coronary heart disease, stroke, venous thromboembolism, and pulmonary embolism compared to women randomized to placebo. To ascertain the effect of this pivotal announcement in community-based delivery settings, the CRN received an NCI administrative supplement to conduct an observational cohort study using automated pharmacy dispensing data. This study, led by Dr. Diana Buist (GHC), provided important information on the rapid translation of the WHI results into clinical practice, use of HT in relation to current clinical recommendations, and patterns of re-initiation after cessation. These findings demonstrate the CRN’s ability to rapidly examine changes in therapies over time. A follow-up study being conducted by NCI investigators in collaboration with two CRN sites is examining these data at the individual patient level to determine the association between patterns of HT usage and subsequent breast cancer occurrence. The results of this study will be utilized to improve the specification of breast cancer natural history used in the prevention component of breast cancer simulation models (Cancer Intervention and Simulation Modeling Network [CISNET]).
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