Abstract 3754: High staining reproducibility and scoring precision demonstrated in endometrial cancer stained with PD-L1 IHC 22C3 pharmDx used in conjunction with combined positive score
Authors: Hand Julia , Morones Amber , Moquin Deanna , Martyniuk Kelly , Kalpakoff Megan , Tabuena-Frolli Siena , Milo Jay , Hund Stephanie 
Published: March 2024

Abstract
Background: PD-L1 IHC 22C3 pharmDx (SK006) is a qualitative immunohistochemical (IHC) assay using anti-PD-L1 clone 22C3 to detect PD-L1 in formalin-fixed, paraffin-embedded (FFPE) human endometrial cancer (ENDO) tissues. PD-L1 expression is determined using the Combined Positive Score (CPS) algorithm, which is the number of PD-L1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100. Validation testing evaluated the sensitivity and analytical performance of SK006 PD-L1 expression in FFPE ENDO specimens based on two PD-L1 expression cutoffs for all applicable studies: CPS ≥ 1 and CPS ≥ 10. Analytical performance studies included precision (combined precision, intra-run and intra-inter observer) and robustness (time, temperature, pH and re-use) testing.
Methods: FFPE ENDO specimens were stained with SK006 and scored using CPS. Negative percent agreement (NPA), positive percent agreement (PPA), and overall agreement (OA) with two-sided 95% bootstrap confidence intervals (CIs) were used for data analysis, based on PD-L1 binary status (positive/negative) at the evaluated cutoffs. Acceptance Criteria (AC): the lower bound of the two-sided 95% CI computed on percent agreement (NPA, PPA, and OA) must meet or exceed 85%. Sensitivity determined if SK006 could detect a range of CPS expression levels in ENDO specimens. Combined precision measured inter-instrument, -operator, and -day variation nested within the same study. Intra-run measured repeatability within the same run and Inter/Intra-Observer measured scoring reproducibility by 3 pathologists over 3 non-consecutive days. Robustness evaluated the staining performance of SK006 under varying Target Retrieval Solution (TRS) laboratory conditions: time (18-22min), temperature (95-99°C), pH (5.9-6.3) and re-use (up to 3 uses).
Results: The sensitivity data showed that SK006 could detect a range of CPS expression levels in ENDO specimens. Analyses for each analytical validation study, subject to AC, showed NPA, PPA, OA point estimates (PE) of ≥ 95.5% and CI lower bounds (CILB) of ≥ 87.1%.
Conclusion: PD-L1 IHC 22C3 pharmDx (SK006) used in conjunction with CPS provides high staining reproducibility and scoring precision for ENDO specimens at the CPS ≥ 1 and CPS ≥ 10 cutoffs, under standard day-to-day laboratory testing and scoring conditions.
Citation Format: Julia Hand, Amber Morones, Deanna Moquin, Kelly Martyniuk, Megan Kalpakoff, Siena Tabuena-Frolli, Jay Milo, Stephanie Hund. High staining reproducibility and scoring precision demonstrated in endometrial cancer stained with PD-L1 IHC 22C3 pharmDx used in conjunction with combined positive score [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3754.