The 16 PALB2-associated breast cancers analyzed by WES were found to harbor a higher number of somatic mutations (median 113.5, range 59–269) than the 683 ER−/HER2− and ER+non-BRCA1/2/PALB2-associated breast cancers (median 51, range 2–6666; P < 0.002, Mann–Whitney U test), difference that remained significant upon 1:3 bootstrap resampling (P = 0.002, see Methods). Here, ESR1 is linked to breast cancer.