Assessment of Heterogeneity of PD-L1 Expression in NSCLC, HNSCC, and UC with Ventana SP263 Assay.

e14502 Background: Clinical assessment of PD-L1 status relies on the result of testing 1 FFPE section per patient (pt). Heterogeneity of PD-L1 expression within a single tissue block and between paired blocks from the same pt could impact pt classification. This study characterizes the intra-block and intra-case heterogeneity using the VENTANA PD-L1 (SP263) Assay in non-small cell lung cancer (NSCLC), head and neck squamous cell carcinoma (HNSCC) and urothelial carcinoma (UC) for tumor cell (TC) and immune cell (IC) staining. Methods: Two blocks from the same tumor for 5 cases of each of 3 indications (30 unique blocks) representing a range of PD-L1 staining were commercially acquired and sectioned serially at 4 μm. Tumor continuity throughout the blocks was confirmed by staining sections 1 and 51 with H&E. Sections 2, 25 and 50 were stained with VENTANA SP263 and scored by a single trained pathologist, using the SP263 scoring algorithm and interpretation guide. Total percentages of PD-L1+ TCs and ICs were determined. Multiple diagnostic cutoffs were applied to TC and IC scores from multiple sections within each block and pair of blocks to establish overall percentage agreement (OPA) within and between blocks at each cutoff. Additional data were available in NSCLC for 200 cases with repeat SP263 staining (minimum separation 70 μm). Results: TC PD-L1 status at all cutoffs showed no intra-block (sections ~100 μm apart) or intra-case heterogeneity (Table). IC PD-L1 status showed limited intra-block and intra-case heterogeneity, with IC % staining in discordant sections varying by no more than 5%. Results are supported by the 200 NSCLC cases, with a minimum TC OPA across cutoffs of 91% (78.5% for ICs). Conclusions: Intra-block and intra-case concordance of TC PD-L1 status is high, and IC PD-L1 agreement is good across cutoffs. This supports the reproducibility of pt PD-L1 status in NSCLC, HNSCC and UC, within and between blocks. [Table: see text]