TGFB1 and neoplasm: Although we previously confirmed 44 that the peak TGF-β1 concentration in the supernatant is significantly higher (approximately 10-fold higher) for L929 cells in vitro than for fibroblasts in vitro, 25 ng/ml exogenous TGF-β1 still promoted L929 cell proliferation, indicating that TGF-β1 can induce strong and stable tumor cell proliferation.