PDCD1 and obesity due to melanocortin 4 receptor deficiency: Dense stroma‐induced hypoxia stabilizes HIF‐1α and, in concert with obesity‐related cytokines (such as IL‐6, TNF‐α, and leptin), activates the JAK/STAT3 pathway, upregulates PD‐1/PD‐L1 expression, and suppresses antigen presentation [17, 142].