Given the putative pathological role of GM-CSF and M-CSF in synovitis (24–26), our aims were to seek diagnostic/prognostic biomarkers by analyzing potential differences in GM-CSF expression and its cellular source, and CD163+ macrophage polarization and density in joints of patients with UA evolving to RA or PsA compared with persistent UA and established RA or PsA, respectively. The gene discussed is CSF1; the disease is rheumatoid arthritis.