CXCL8 and thyroid cancer: In particular, the results indicate a more consistent inhibitory effect of vitamin D on CCL2 secretion, which was observed in both thyroid cell types and at several concentrations tested, as compared to CXCL8, which was reduced only in TPC-1 and only by using the highest concentration of vitamin D. This observation would indicate that different pathways are involved in the secretion of CXCL8 and CCL2 in thyroid cancer cells.