Association Between Programmed Death Ligand 1 Expression in Patients With Basal Cell Carcinomas and the Number of Treatment Modalities.

Importance: Response to programmed death 1 (PD-1) inhibitors has been associated with programmed death ligand 1 (PD-L1) expression levels in several cancers, but PD-L1 expression and its clinical significance in basal cell carcinoma (BCC) are unknown to date.

Objective: To assess PD-L1 expression in treatment-naive and treated BCCs.

Design, Setting, and Participants: This investigation was a cross-sectional study at a single academic tertiary referral center. Immunohistochemical staining on formalin-fixed BCCs from a dermatology clinic were examined in masked fashion by a dermatopathologist and a dermatologist. The study dates were March 31, 2014, to June 7, 2016.

Exposures: Treated BCCs (including those recurrent after surgery, radiotherapy, systemic chemotherapy, or topical chemotherapy) vs treatment-naive BCCs.

Main Outcomes and Measures: Percentage of tumor cells and tumor-infiltrating lymphocytes (TILs) with PD-L1 expression, intensities of expression, and association with treatment modalities.

Results: Among 138 BCCs from 62 patients (43 males and 19 females; mean [SD] age at biopsy, 61.6 [13.7] years), 89.9% (124 of 138) were positive for PD-L1 expression in tumor cells, and 94.9% (131 of 138) were positive for PD-L1 expression in TILs, defined as greater than 5% positive immunohistochemical staining in the respective cell populations. The PD-L1 immunohistochemical staining intensity of 78 treated BCCs compared with 60 treatment-naive BCCs was significantly different in tumor cells (32% vs 7%, P = .003) and TILs (47% vs 18%, P = .008) after adjusting for the age at diagnosis. In a multivariable model adjusting for age, sex, and BCC location, PD-L1 staining intensity in tumor cells increased with the number of distinct prior treatment modalities (median, 0.12; interquartile range, 0.03-0.20; P = .007).

Conclusions and Relevance: Our data suggest that PD-1 immunotherapy may have activity against BCCs, including in those that have been previously treated. This hypothesis needs to be tested in future clinical trials.