BRCA1 and breast cancer: However, conclusions were limited by small sample size, lack of a comparable control population, and/or inability to evaluate those with BRCA1 vs BRCA2 mutations separately.10, 11, 12, 13, 14 Thus, we performed a multicenter, retrospective, matched cohort study to compare the frequency, severity, and timing of hematologic toxicities occurring throughout the multicycle curative intent chemotherapeutic regimens for breast cancer in women with and without an inherited BRCA1 or BRCA2 mutation.