Currently, predictive markers for ICIs therapy in melanoma include lactate dehydrogenase (LDH) [5], tumor-infiltrating lymphocytes [6], programmed cell death protein 1 (PD-1) expression [7–9], tumor mutation burden (TMB) [10], the host’s gastrointestinal microbiome [11, 12], and body-mass index [13], but these markers are not sufficient to predict prognosis. The gene discussed is PDCD1; the disease is neoplasm.