Mechanistically, hypoxia acts through tumor-fibroblast crosstalk to increase IL-6 expression in fibroblasts; in turn, fibroblast-derived IL-6 induces expression of arginase 1 (ARG1), a key mediator of immunosuppression, in macrophages via activation of the JAK/STAT signaling pathway. The gene discussed is ARG1; the disease is neoplasm.