No obvious difference was observed in the degree of bi-allelic loss between ER+ and ER- breast cancer tumour subtypes, where 33/37 (89%) ER+ with BRCA mutations, and 29/30 (97%) ER- with BRCA mutations were found to have bi-allelic loss, including two ER- patients with composite heterozygous mutations (one patient had two deleterious mutations in BRCA1 and one patient had two deleterious mutations in BRCA2) (Supplementary Table 1). Here, BRCA1 is linked to breast carcinoma.