Among the 55 patients in our cohort who had dual cancers in the breast and lung, we identified variants in 10 DNA damage repair genes in 12 patients, which included FANCA, PALB2, BRCA2, BRIP1, RAD51D, TP53, ERCC6, MSH2, WRN, and FANCI, with PALB2, BRCA2, RAD51D, TP53 and PTEN being known breast cancer susceptibility genes [14–17]. This evidence concerns the gene PTEN and breast cancer.