BRCA1 and breast cancer: 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).