G-CSF associates with poor survival in cutaneous melanoma and promotes metastasis through coordinated effects on macrophages and tumor cells

Macrophage-melanoma interactions critically shape the tumor microenvironment, yet the cytokine networks driving this process remain incompletely understood. Among these, colony-stimulating factors--particularly granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF or CSF3)--regulate myeloid cell behavior during cancer progression, although their specific roles in melanoma remain unclear. Using co-culture systems of melanoma and monocyte-derived macrophages, we found that GM-CSF-primed macrophages induced robust G-CSF secretion and concurrent CSF3 upregulation in both cell compartments. Moreover, transcriptomic profiling of patient-derived tumor-associated macrophages (TAMs) confirmed elevated CSF3 and CSF3R expression in metastatic melanoma. Multiplex immunofluorescence analysis of a stage II-IV primary melanoma cohort (n=84) revealed increased G-CSF and CD114 expression in TAMs and tumor cells from patients who subsequently developed metastasis. High G-CSF levels in either TAMs or melanoma cells emerged as an independent prognostic factor for shorter disease-free and overall survival (p < 0.001). Mechanistically, G-CSF activated STAT1/STAT3 signaling in melanoma cells and promoted proliferation and invasion in a CD114-dependent manner. Of note, G-CSF drove monocyte differentiation toward a distinct inflammatory macrophage state characterized by STAT1/STAT3 activation and a pro-invasive secretory profile. Furthermore, melanoma cells conditioned by G-CSF-differentiated macrophages displayed increased in vivo lung colonization and enriched transcriptional programs linked to invasion and proliferation. Collectively, these findings establish the G-CSF/CD114 axis as a potential clinically relevant driver of melanoma metastasis and identify G-CSF as a novel independent prognostic biomarker.

Nieto-Valle, A., Barandalla-Revilla, L., Lopez-Navarro, B., Barrio-Alonso, C., de Francisco-Lopez, A., Aviles-Izquierdo, J. A., Parra Blanco, V., Sanchez-Mateos, P., Samaniego, R.

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