C3 and metastatic melanoma: However, recent studies showed that a marker for collagen type III fibrogenesis (PRO-C3) with high PRO-C3 in patients’ serum is a predictor of poor overall survival in metastatic melanoma upon treatment with anti-CTLA-4 and anti-PD-1 therapy (Jensen et al., 2018; Hurkmans et al., 2020).