PD-L1 Expression in Sarcomas: An Immunohistochemical Study

Abstract Introduction/Objective Immunotherapy is increasingly used for the treatment of metastatic melanoma and carcinomas. PD-I (programmed death 1) and its associated ligand (PD-L1) inhibits the activation of T lymphocytes. This inhibition can be impacted by a number of drugs. Response to these drugs is predicted by assessment of PD-L1 expression. PD-L1 expression varies between 19% and 92% in melanomas and carcinomas. PD-L1 expression is less well documented for sarcomas. Methods Fifty-one sarcomas of various histopathologic types were immunohistochemically stained (IHC) for PD-L1 using the antibody clone SP263 (Ventana, Tuscan, AZ). Membrane staining of tumor cells was quantitated as a percentage of total tumor cells. Sarcomas were judged as non-expressors (less than 1%) low-expressors (1 to 50%) and high expressors (greater than 50%). The percentage of each type of sarcoma judged as an expressor was determined. Results The percentage of each type of sarcoma expressing PD-L1 is reported and 20% of sarcomas expressed PD- L1. The percentage of sarcomas expressing PD-L1 varied significantly between types but the majority of sarcomas were non-expressors. Conclusion PD-L1 IHC expression is valuable in predicting response to immune-modulating drugs. Such therapies may be useful for treatment of metastatic sarcomas. Expression of PD-L1 in carcinomas and melanomas is variable ranging from 19% to 92%. In our study, a minority (20%) of sarcomas expressed PD-L1. Other studies have shown similar results with between 1.4 and 59% (average 24%) of sarcomas expressing PD-L1. Expression appears to be type specific. These finding suggest that PD-L1 based therapy may be less useful in sarcomas than in other malignancies.