PD-L1 assessment in FNA (EBUS) dervied samples.

Abstract

11615 Background: Pembrolizumab therapy for non-small cell lung cancer requires PD-L1 immunohistochemistry (IHC). FDA approval was based on staining of resections or core biopsies. Little is known about PD-L1 expression in fine needle aspiration (FNA) specimens including EBUS of mediastinal lymph nodes. Methods: IHC was performed using the PD-L1 IHC 22C3 pharmDx test on formalin fixed paraffin embedded FNA cell blocks of 8 squamous cell carcinomas and 15 adenocarcinomas (ACA) (age: 42-84, mean: 63, median: 63; 11 female and 12 male). Mutation data (50 gene NGS panel, and ALK, ROS1, RET and MET FISH) was available for 14 ACA. Membranous PD-L1 staining of any intensity and extent was recorded in at least 100 tumor cells (tumor proportion score). The tumors were grouped as: no staining (<1%), low expression (1-49%) and high expression (50% or more). Results: Six (26%) tumors showed no staining, 6 (26%) low expression and 11 (48%) high expression (table 1). High PD-L1 expression was seen in 1 ALK, 1 braf, 1 EGFR, 1 Her2 exon20, 2 kras mutated tumors and 2 tumors with no or unknown mutation status, low PD-L1 expression in 1 braf and 1 EGFR mutated case and 1 tumor without mutation. No expression was seen in 1 ROS1, 1 kras mutated tumor and 1 tumor without mutation. One EBUS biopsy also had PD-L1 assessed on a transbronchial biopsy of the primary tumor showing similar staining (30% versus 20%). Conclusions: PD-L1 immunohistochemistry appears to be feasible using cell blocks of fine needle aspirates containing adeqaute number of viable tumor cells. The majority of ACA were also adequate for NGS mutation and FISH analysis. High PD-L1 expression was seen in approximately half the tumors, which is greater than has been observed in resections/core biopsies, this finding merits further study. High expression of PD-L1 was seen in both squamous cell carcinoma and adenocarcinoma, and tumors with and without common driver mutations. [Table: see text]