This was observed as early as day 1 in serum-free cocultures (dashed line on Co-Cult bar in Fig. 5A; left graph) and, by day 2, a 1.5–2.1 fold increase in MCP-1 was observed in both media cocultures over the simple sum of sarcoma cells and bone alone (Fig. 5A; P < 0.001). Here, CCL2 is linked to sarcoma.