Many candidate genes that may cause breast cancer have been identified in the past few years including high penetrance genes (BRCA1/2, TP53 and PTEN), moderate penetrance genes (ATM, CHEK2, PALB2 and BRIP), and low penetrance genes (FGFR2, ESR1 and TOX3) [2–7]. This evidence concerns the gene TOX3 and breast cancer.