TGFB1 and osteosarcoma: TGFβ functions as a protumor factor to promote primary tumor growth and dissemination of metastases in sarcomas, and TGFβ level has been associated with advanced and metastatic osteosarcoma in clinical samples.49, 50 In the sarcoma microenvironment, TGFβ is mainly expressed by tumor cells and stromal cells (e.g., CAFs, endothelial cells) and triggers ECM factor expression.