Targeted sequencing in 14 breast cancers from individuals harboring an NTHL1 heterozygous variant (NTHL1-het) identified somatic mutations in breast cancer driver genes including TP53 (6/14 cases), PIK3CA (3/14 cases), MAP3K1 (3/14 cases), and GATA3 (2/14 cases) (Fig. 1a). Here, MAP3K1 is linked to breast cancer.