PDCD1 and neoplasm: However, the tumor lesion in this case was difficult for biopsy for its anatomic location, resulting that the level of PD-L1 protein expression on tumor cells could not be accurately detected before the initiation of anti-PD-1 therapy, which exist a possibility that PD-L1 expression in tumor milieu might be low level or even negative and therefore lead to the failure of anti-PD-1 treatment.