MRC1 and melanoma: Previous studies have shown that polyamines play an important role in regulating macrophage polarization and function [33], while polyamine blocking therapy (PBT) increased M1 macrophages in the TME of syngeneic murine ovarian cancer [32] but decreased immunosuppressive CD206+F4/80+ M2-like TAMs in syngeneic murine melanoma and colon cancers [31, 34].