Thus, SHBG is a very important “regulator” of the level and, accordingly, the activity of sex hormones (testosterone, estrogens) in the body (a high level of SHBG leads to a low content of free steroids, and, accordingly, a low level of SHBG causes an increase in the concentration of bioavailable sex hormones), which may be of paramount importance for the pathophysiology of BC [13,14,16,21]. The gene discussed is SHBG; the disease is breast cancer.