Of the nine tumors lacking BRCA1 locus-specific LOH, three came from patients with a history of receiving chemotherapy for a prior cancer, and three were tumors of types not typically associated with BRCA1 germline mutations (an ovarian carcinosarcoma, one ER+ breast ductal carcinoma, and one ER+ breast lobular carcinoma), suggesting that second primary and non-classic histological tumors may be enriched for absence of locus-specific LOH. This evidence concerns the gene BRCA1 and breast lobular carcinoma.