SPP1 and lung carcinoma: In vitro coculture of CTC lines obtained from lung cancer patients with peripheral blood mononuclear cells resulted in the induction of monocyte differentiation into TAMs, which secreted OPN (SPP1), MMP9, chitinase-3-like-1 (YKL-40), and the platelet factor responsible for leukocyte recruitment, migration, and invasion [203].