Considering the latter, hormonal factors seem to play an important role in the development of BC in women and mice carrying the c.1100delC mutation, since the vast majority of BCSs in women is of the luminal/ER+ subtype [6, 7] and Chk2 c.1100delC knock-in mice developed tumors preferentially in females [18]. This evidence concerns the gene CHEK2 and breast cancer.