Breast cancers may display defects in DNA repair such as mutations in key DNA damage response and repair proteins such as breast cancer-susceptibility gene (BRCA1/2) and tumor suppressor protein p53 (TP53), and altered expression levels of DNA repair proteins thymine-DNA glycosylase (TDG) and poly(ADP-ribose) polymerase 1 (PARP1) [1–3]. This evidence concerns the gene TDG and breast cancer.