Coculture of phosphoserine aminotransferase 1 (PSAT1cKO) BMDMs with melanoma or lung cancer cell lines showed a significant diminution of the suppressive M2 macrophage phenotype suggesting that serine biosynthesis promotes the immunosuppressive M2 phenotype via the PERK-ATF4 pathway. This evidence concerns the gene EIF2AK3 and melanoma.