CCL2 and cancer: However, a major source of CCL2 may not be cancer cells or TECs but stroma in these models because there was no significant correlation between the number of TAMs and mRNA levels of human CCL2 in MDA-MB-231 breast cancer cells; however, there was a significant correlation between the number of TAMs and mouse CCL2 in the stroma (Fujimoto et al. 2009).