PDCD1 and neoplasm: The expression of PD-1 and PD-L1, along with the prognostic relevance of TIL, was also investigated in pediatric gonadal germ cell tumors, a heterogeneous group of tumors which represent 3–5% of all childhood cancers occurring before 15 years of age, and 15% of neoplasms in adolescents aged 15–19 years [111].