The role of M1 macrophages in tumor progression has recently been studied by Podlesnaya et al., who hypothesize that cytotoxic M1 macrophage activity may promote tumor progression via facilitating tumor immune escape (35) and in esophageal squamous cell carcinoma via GDF15-mediated ErbB2 phosphorylation (36). Here, GDF15 is linked to esophageal squamous cell carcinoma.