Exposure of breast cancer cells to alkylating and DNA damaging agents induces the expression of EXO1. In view of the observed correlation between elevated EXO1 expression and activated genomic instability related gene-set in breast tumors (Figure 3A), this observation suggests the possibility that prolonged EXO1 expression in breast cancer is indicative of un-rectified DNA repairs. This evidence concerns the gene EXO1 and breast cancer.