These latter observations in HNSCC were further qualified by more recent studies in which analysis by PCR and immunohistochemistry of 41 esophagectomy tumors identified elevated levels of PD-L1 to be associated with a poor prognosis particularly in advanced tumors (76), while another study, however, did not find a clear correlation between tumor cell expression of PD-L1 and poor prognosis, but did identify elevated expression of PD-L1 on infiltrating immune cells, including T cells, macrophages and dendritic cells, to correlate significantly with increased overall survival (77). This evidence concerns the gene CD274 and head and neck squamous cell carcinoma.