TGFB1 and neoplasm: Osteoclasts release various growth factors, such as TGFβ, at bone resorption sites, stimulating tumor cell proliferation and eventually establishing a vicious cycle between tumor growth and bone absorption.31, 32, 33 Chondroblastic, recurrent, and lung metastatic OS lesions have lower osteoclast infiltration than primary osteoblastic OS lesions.34