Firstly, SHBG is of paramount importance in regulating the level of bioavailable (active) testosterone and estrogens in the female [18,19,38,39,40,42], and due to this (the modulation of the phenotypic effects of testosterone and estrogens), it can be involved in the BC pathophysiology (these mechanisms will be discussed in detail below) [39,42,43,45]. The gene discussed is SHBG; the disease is breast cancer.