PD-L1 expression in cutaneous squamous cell carcinoma correlates with risk of metastasis.

BACKGROUND: Programmed cell death ligand 1 (PD-L1) expression in primary cutaneous squamous cell carcinoma has not been described.

METHODS: We reviewed immunohistochemical stained sections of 40 primary and five metastatic cutaneous squamous cell carcinomas using antibody to PD-L1 and classified the staining pattern according to the DAKO tumor proportion score method. We compared the staining results with microscopic staging parameters associated with risk of metastasis including tumor diameter, histologic grade, tumor thickness and perineural invasion.

RESULTS: PD-L1 expression was present in 4 of 20 low risk tumors (20%), all of which showed low expression. PD-L1 expression was present in 14 of 20 high risk tumors (70%), 12 of which showed low expression and 2 of which showed high expression, 5 of 5 metastases (100%), with three showing low expression and two showing high expression.

CONCLUSIONS: This survey documents PD-L1 expression in cutaneous squamous cell carcinoma and shows a positive correlation between the degree PD-L1 expression and pathologic findings related to risk of metastasis including large diameter, higher histological grade and tumor thickness.