CD274 and nasopharyngeal carcinoma: Based on the available evidence on the probable effects of the elements on the immune system and cancer development and the few available reports on the association of PD-1 and its ligand PD-L1 in the development and progression of cancer, especially in the context of nasopharyngeal cancer, it seems important to undertake additional studies to determine the level of PD-L1 expression on selected cells of the immune system and its correlation with the levels of iron, copper and zinc in the body of patients.