These results suggest that PALB2-associated breast cancers with bi-allelic inactivation are more often HR-deficient than non-BRCA1/2/PALB2-associated breast cancers despite displaying a similar prevalence of ER-positive luminal breast cancers, and that PALB2-associated breast cancers without bi-allelic inactivation appear to resemble non-BRCA1/2/PALB2-associated breast cancers. The gene discussed is ESR1; the disease is breast cancer.