In a study conducted by Johnson et al., the authors analyzed two independent cohorts of melanoma patients treated with anti-PD-1 therapy, and they highlighted that malignant cells, particularly melanoma cells, with high levels of HLA-DR are more responsive to PD-1 antibodies due to their inflammatory signals, even in patients with poor prognosis, such as those with liver metastases [105]. This evidence concerns the gene PDCD1 and melanoma.