The study of normal breast epithelium from BRCA mutation carriers may yield insights into the early natural history of breast tumorigenesis. In studying the potential role of altered hormone receptor expression, King et al. found that expression of the progesterone receptor was significantly more common in benign breast epithelium adjacent to invasive breast carcinoma in BRCA1 heterozygotes compared to matched tissues from women without mutations. This finding suggests that deregulation of progesterone receptor expression, as a result of BRCA1 haploinsufficiency, may represent an early event in BRCA1-linked breast tumorigenesis and has implications for chemoprevention in this high-risk population. For details, see the article by King et al. on page 5051 of this issue.

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