TGFB1 and bone neoplasm: While the level of TGF-β in the C4-2 TGF-β cell line supernatant (6,000 pg/mL) is in line with reports in murine bone tumor models (~2,000 pg/mL), it could underestimate the levels present in the TME in prostate cancer patients, which have been reported to be as high as 25,000 pg/mL (13).