We undertook a WES-based approach in affected first-degree cousins, to identify candidate gene variants for hereditary BC (HBC), and identified damaging variants in NPL (N-Acetylneuraminate Pyruvate Lyase), POLN (DNA Polymerase Nu), RASAL1 (RAS Protein Activator Like 1) and ROS1 (ROS Proto-Oncogene 1, Receptor Tyrosine Kinase)genes. This evidence concerns the gene POLN and breast cancer.