CD274 and neoplasm: Among the known predictive factors of the response to ICIs, PD-L1 expression is commonly weak and restricted to tumor-infiltrating lymphocytes (TILs) rather than tumor cells in GEP-NECs [51], while a high microsatellite instability status and a high tumor mutational burden have been observed in less than 10% of GEP-NECs [51,52].