2023P - Evaluating the prevalence of the expression of PD-L1 in NSCLC specimens with short-duration formalin fixation using IHC 22C3 pharmDx

Abstract

BackgroundImmune checkpoint inhibitors mediated by PD-1 and PD-L1 are promising treatments for various tumors. The PD-L1 expression in tumor cells was found to be correlated with the likelihood of a response to PD-1- or PD-L1-targeted therapy in non-small cell lung cancer (NSCLC). For PD-L1 immunohistochemistry (IHC), 22C3 pharmDx is the only companion diagnostic assay that can identify NSCLC patients suitable for pembrolizumab treatment. Specimens are scored and divided into 3 categories (<1%, 1-49%, ≥50%) based on the tumor proportion score (TPS). The PD-L1 prevalence in NSCLC patients screened for the KEYNOTE-024 trial was 31% with TPS <1%, 39% with TPS 1-49%, and 30% with TPS ≥50%. While specimens used for the IHC 22C3 assay are recommended to be formalin-fixed for 12-72h, the specimens were fixed in 10% neutral-buffered formalin for less than 6h in our institution. Thus, we retrospectively assessed the PD-L1 prevalence in NSCLC patients to determine whether the PD-L1 TPS differs according to the duration of formalin fixation. MethodsWe screened consecutive NSCLC patients who underwent tumor biopsy by bronchoscopy between January 2017 and June 2018 at National Hospital Organization Fukuokahigashi Medical Center. In the present study, we only included 70 patients whose tumors were formalin-fixed for less than 6h and whose PD-L1 expression had been evaluated by IHC with antibodies to human PD-L1 (22C3 pharmDx). ResultsThe PD-L1 prevalence in patients with NSCLC in our hospital was 26 (37%) with TPS<1%, 23 (33%) with TPS 1-49%, and 21 (30%) with TPS ≥50%, suggesting that small biopsy samples obtained by bronchoscopy that were formalin-fixed for <6h are suitable for PD-L1 IHC. We also performed analyzed in 35 surgically-resected NSCLC specimens that had been formalin-fixed for 1-7 days by PD-L1 IHC. The PD-L1 prevalence was 20 (57%) for TPS < 1%, 9 (26%) for TPS 1-49%, and 6 (17%) for TPS ≥50%. ConclusionsThe PD-L1 prevalence in specimens with short-duration formalin fixation was consistent with the results of the KEYNOTE-024 trial. We will present our conclusion regarding these results, including the characteristics of patients and the PD-L1 prevalence in specimens fixed for 12-72h in our institution, from July 2018 onward. Legal entity responsible for the studyNational Hospital Organization Fukuokahigashi Medical Center. FundingJSPS KAKENHI JP18K15927. DisclosureAll authors have declared no conflicts of interest.