CD274 and cancer: Although PD-L1 expression in cancer has been defined as a prognostic factor not only in patients receiving conventional treatments, but also in patients receiving immunotherapy targeting PD-1 or PD-L1 [42], previous studies have reported conflicting conclusions about the prognostic value of PD-L1 expression in OSCC, even in some meta-analyses, including large quantities of data [43,44,45].