HRD extends beyond BRCA1/BRCA2 mutations to include non-BRCA genes (RAD51C/RAD51D, BRIP1, BARD1, ATM, PALB2), broadening actionable targets across ovarian and breast cancer subtypes, including HER2-positive (30–40%) and luminal subtypes (15–25%). Here, ERBB2 is linked to breast cancer.