PDCD1 and metastatic neoplasm: In an attempt to evaluate the predictive role of methylation for the identification of patients with advanced metastatic HNSCC who would respond to anti-PD-1 immune checkpoint inhibitors (ICIs), >850,000 CpG sites were studied in patients with relapsed or metastatic disease after receiving platinum chemotherapy or who subsequently received anti-PD-1, regardless of their response to the treatment [81].