Based on the overall similar mutation patterns between breast cancers in carriers of germline deletion of APOBEC3B genes and non-carriers, and a higher occurrence of somatic mutations on the TCW motif in APOBEC3B deletion samples, we speculate that germline deletion of APOBEC3B, expression of APOBEC3B and APOBEC3C, and somatic mutation may interact in contributing to breast cancer. This evidence concerns the gene APOBEC3C and breast cancer.