The tumor microenvironment consists of immune cells, as well as other non-cancerous cells such as adipocytes, fibroblasts, blood vessels, signaling molecules, and the extracellular matrix.[28] GDF-15 may promote immune evasion and immune rejection of tumor cells by modifying the tumor microenvironment, thereby facilitating tumor progression.[17] There are 2 types of innate immune cells called macrophages: M1 and M2. This evidence concerns the gene GDF15 and neoplasm.