An IL-34-IGF-1 inflammatory axis fuels KRAS-mutant lung cancer progression.

Macrophages are innate immune cells of embryonic or adult origin with tissue specific roles in homeostasis, disease surveillance, and wound repair that can be co-opted to promote tumor growth and spread 1-11 . An understanding of the specific roles of macrophage subsets in lung tumor initiation and progression could promote new therapeutic approaches for this deadly disease. Here, we show that KRAS G12D mutations in lung epithelium drive proliferation of resident, embryonically-derived alveolar macrophages, which then promote tumor cell proliferation and protection from ferroptosis, leading to tumor progression. Using genetically engineered mouse models of mutant KRAS G12D non-small cell lung cancer 12,13 , we found that alveolar macrophages accumulate by proliferation in response to tumor cell-secreted IL-34, recapitulating events observed in late embryonic lung development. Tumor alveolar macrophages in turn drive IGF-1-dependent tumor cell proliferation. Neutralization or deletion of IL-34 suppresses IGF-1 expression, reduces macrophage and tumor cell proliferation and inhibits tumor progression. High IL34 and IGF1 correlate with poor survival in KRAS G12D/V lung adenocarcinomas and in other solid tumors, indicating that bi-directional proliferative signaling between resident macrophages and tumor cells can drive human lung tumor progression. These studies identify resident macrophage-tumor cell interactions as key interception points for lung cancer therapy.