CCL2 and sarcoma: Analysis of secreted paracrine factors revealed that MMP-2, TGF-β1 and MCP-1 were not detectable in cultures of parental (P) or bone-seeking (BO) cells alone, but were present in femur alone cultures and cocultures in concentrations comparable to those observed in sarcoma cultures (Fig. 7B, C, D; also see Fig. 4, 5).