Interestingly, 4T1 cells that metastasized to the lung constitutively expressed higher levels of CCL2 than the original 4T1 cells, and intravenous injection of 4T1 cells producing a higher level of CCL2 resulted in increased numbers of tumor foci in the lungs of WT and Ccl2-/- mice. Here, CCL2 is linked to neoplasm.