Moreover, our prognostic analysis revealed that the higher expression levels of C3 in COAD, GBM, KIRC, LGG, and LUSC; C3AR1 in GBM, LGG, and COAD; C5 in COAD, KICH, STAD, and UVM; and C5AR1 in THCA tumors are associated with a shorter survival duration of the cohorts. Here, C5 is linked to glioblastoma.