In this study, we evaluated the in situ activation of the complement system (PTX3, C1q, C3aR, C5aR, CD59, and C5b-9) and characterized the immune cell infiltration (mast cells, macrophages, CD4, and CD8+ T cells) in correlation with the different expressions of MUC1 in a cohort of patients with ccRCC. The gene discussed is C5AR1; the disease is nonpapillary renal cell carcinoma.