When restricting the comparison to the 18 ER+/HER2− PALB2-associated breast cancers and the 441 ER+/HER2− non-BRCA1/2/PALB2-associated breast cancers, the differences were less overt, with more frequent 16p gains and 16q losses in the non-BRCA1/2/PALB2-associated breast cancers (P < 0.05, Fisher’s exact test and bootstrapping-corrected; Supplementary Fig. 4b). This evidence concerns the gene BRCA1 and breast cancer.