ESR1 and cancer: In single covariate models, ER+ BRCA1 cancers were found less often than ER- BRCA1 cancers to be of pure invasive ductal type (P < 0.001), to be histologic grade 3 (P < 0.001), to possess a high mitotic rate (>10 mitoses per 10 high powered field (HPF); P < 0.001), to have a moderate/marked lymphocytic infiltrate (P = 0.003), to have either geographic necrosis or a fibrotic focus (P < 0.001) or to have pushing (or unknown) margins (P < 0.001).