MS4A4A and neoplasm: In the immune checkpoint examination, a significant negative correlation existed between PCSK9 and CD163, V-set and Ig domain-containing 4 (VSIG4), and membrane spanning 4-domains A4A (MS4A4A), which encode proteins exhibited on the surface of M2 macrophages, indicating the relationship with M2 macrophage polarization in the tumor microenvironment (41, 42).