Activated similar to M2 macrophages [105, 106], TAMs express substantial amounts of ARG1, leading to an over-production of ornithine, which can be used by ODC to synthesize polyamines, such as putrescine, spermidine, and spermine, and thus promote cancer cell proliferation and tumor vascularization [270, 271]. Here, ARG1 is linked to neoplasm.