PD-L1 Expression on Cell Block Preparations of Pancreatic Adenocarcinoma

Abstract

Abstract Objectives Programmed death-ligand 1 (PD-L1) is an emerging molecular target in anticancer therapy, most notably non–small cell lung cancers. PD-L1 expression in pancreatic adenocarcinomas (PDAs) on surgical specimens is highly variable, with 10% to 60% of tumors showing expression. PD-L1 expression in PDA on endoscopic ultrasound-guided fine needle aspirations (EUS-FNAs) has been rarely studied. Methods Formalin-fixed, paraffin embedded (FFPE) cell blocks (CBs) from 65 EUS-FNA samples of 55 patients, with a diagnosis of PDA, with at least 20% tumor cellularity were retrieved. The cell blocks were originally fixed in CytoRich fixative. Immunohistochemical staining (IHC) for PD-L1 was performed using the M365329-1 (22C3) clone according to the manufacturer’s approved protocol and optimized for the fixation method using appropriate controls. A combined positive score (CPS) defined per CAP guidelines as the total number of positive tumor cells and inflammatory cells as a percentage of the total number of tumor cells was assessed for each case and was grouped as <1, 1-20, or >20. Results Twenty-five samples (38%) from 21 patients showed immunoreactivity to PD-L1, with 21 (32%) having a CPS of <1 and four (6%) having a CPS of 1-20. Eight of these 25 samples had surgical correlates, of which concordant staining was noted in five (62.5%). Of the discordant three, decreased tumor cell sampling in the core biopsy was noted in one. Overall, 20 of 21 patients (95%) with PD-L1 immunoreactivity had disease progression with 17 (81%) associated with metastatic disease and three (14%) with locally advanced disease. Conclusion Immunohistochemical analysis for PD-L1 is feasible on EUS-FNA CB samples when optimized and validated for the fixation method using appropriate controls. PD-L1 expression is seen in only a minority of PDAs, albeit with a very low CPS. The potential role of PD-L1 as a prognostic marker for disease progression needs further exploration.