TGFB1 and acute promyelocytic leukemia: Because halofuginone is known to reduce TGF-β signaling pathway in normal cells such as fibroblast [23] and in cancer cells such as melanoma [15] and promyelocytic leukemia [24], and because we recently demonstrated that TGF-β signaling plays a crucial role in the development of lung metastases in osteosarcoma, we then evaluated the effect of halofuginone on TGF-β signaling pathway in osteosarcoma cells.