MDK and neoplasm: Studies have demonstrated that MDK secreted by tumor cells binds to the LRP1 receptor on the surface of macrophages, polarizing macrophages toward the M2 phenotype (59, 60) and promoting the secretion of the cytokine CXCL1. In turn, CXCL1 further recruits immunosuppressive cells and tumor-associated macrophages to support tumor cell growth (60).