BRCA1 and breast cancer: Most breast cancers have relatively low numbers of SNVs and indels, compared to other cancer types, however, approximately 20% of tumours are associated with defective homologous recombination (HR) double strand break repair (e.g., in particular those arising in BRCA1, BRCA2, PALB2, RAD51C germline mutation carriers), and these exhibit high rates of SNVs and indels.