This case-control study evaluated the pathology of BCs developing in carriers of PTVs and/or rare MSVs in 9 BC susceptibility genes: ATM, BARD1, BRCA1, BRCA2, CHEK2, PALB2, RAD51C, RAD51D, and TP53 in a large multicenter collaborative study comprising population-based and hospital-based studies. The gene discussed is ATM; the disease is breast cancer.