In addition, for 5 of the 8 NTHL1-het cancers, the expression of NTHL1 in the breast cancer cells (AE1/AE3 positive cells) was reduced by >30% compared to the surrounding non-cancer cells (AE1/AE3 negative cells) (Supplementary Fig. 4), while only a small proportion of control cancers showed the same phenomenon (5 of 21), suggesting that NTHL1 expression may be attenuated further specifically in the cancer cells of NTHL1 LoF variant carriers. This evidence concerns the gene NTHL1 and breast cancer.