We don’t observe significant differences in the allele frequencies between different regions of Poland, i.e., for BRCA1, PALB2, CHEK2, NBN, RECQL, and also for the GEN1 founder p.Lys645Cysfs*29 variant, neither in breast cancer cases nor in controls (for GEN1 data, see Supplementary Table S1). Here, CHEK2 is linked to breast cancer.