ERBB2 and breast cancer: Further, contrary to expectations that luminal A and B breast cancers are less deadly in young women, a National Comprehensive Cancer Network study of 17,575 women with stage I–III breast cancer reports higher breast cancer mortality in young women with luminal A (HR 2.1; 95% CI, 1.4–3.2) and B (HR 1.4; 95% CI, 1.1–1.9) cancers compared with young women with triple-negative or HER2+ cancers23.