In six tumors with BRCA1 locus-specific LOH, at least 25% of tumor nuclei retained positive BRCA1 staining, indicating intratumoral heterogeneity; two had missense mutations and four had truncating mutations in BRCA1. Four of the five tumors without locus-specific LOH, all with truncating mutations and including both with BRCA1 promoter methylation, showed either diffusely or heterogeneously positive BRCA1 staining in tumor nuclei similar to normal stromal cells (Table 2, Fig. 2c, Supplementary Figs. 7 and 8). Here, BRCA1 is linked to neoplasm.