Adhesion forces between macrophages and cancer cells promote early tumor development

(KP) lung tumor spheroids grown in 3D. Real-time microscopy showed that tissue-resident macrophages, but not monocytes, promote early tumor growth. Using quantitative measurements, we built a physical model that recapitulates cancer cell proliferation dynamics and macrophage-tumor interactions. KP tumor cells grown alone formed a single aggregate that contracted over time due to nutrient limitation, whereas macrophages induced the formation of multiple aggregates that grew, fused, and expanded nutrient access, thereby increasing proliferation. Similar macrophage-driven growth was observed when alveolar or bone-marrow-derived macrophages were cocultured with KP or pancreatic carcinoma cells. The model predicted a redistribution of macrophages toward the periphery of aggregates, a pattern confirmed in vitro and previously observed in vivo. It also identified adhesion forces between tumor cells and macrophages as a key driver of spheroid nucleation and growth. Among candidate integrins, CD11c was highly expressed by alveolar macrophages; CD11c blockade reduced adhesion forces, prevented macrophage-driven spheroid nucleation, and impaired tumor growth. Bone-marrow-derived macrophages required simultaneous CD11b and CD11c blockade for similar effects. Finally, CD11c inhibition in RAG-Knock Out (KO) mice reduced tumor survival probability and slowed the growth of ear-implanted tumors, indicating that CD11c-dependent interactions support tumor establishment beyond the lung. Together, these findings uncover a critical physical mechanism through which macrophages promote early tumor progression.