SHBG and prostate cancer: Additionally, fenretinide does not substantially modulate the levels of several biomarkers in prostate cancer, including transforming growth factor alpha (TGF-α), insulin-like growth factor 1 (IGF-I), insulin-like growth factor binding protein 3 (IGFBP-3), sex hormone binding globulin (SHBG), and prostate-specific antigen (PSA), which are indicative of insufficient biological activity (36, 37).