Baseline serum samples of 45 patients with melanoma treated with dual ICI (anti-CTLA-4 plus anti-PD-1 antibodies) and 44 patients with melanoma treated with anti-PD-1 monotherapy were independently collected across four different dermatology departments (Tübingen, Mannheim and Essen in Germany; St. The gene discussed is PDCD1; the disease is melanoma.