Background: A number of programmed death ligand 1 (PD-L1) immunohistochemistry (IHC) diagnostic (Dx) tests have been approved by the FDA to guide treatment (Tx) with programmed death-1/PD-L1 inhibitors. Here, we evaluate the utilization of the Dako PD-L1 IHC 28-8 and 22C3 pharmDx and Ventana PD-L1 (SP142) assays on real-world samples across multiple tumor types, characterize PD-L1 testing practices among physicians who order a PD-L1 test, and investigate how PD-L1 test results impact physicians’ Tx decision-making and use of immuno-oncology (I-O) Tx.

Methods: 55,652 samples with clinical characteristics were provided by Symphony Health Solutions. NeoGenomics Laboratories, Inc assessed PD-L1 expression between October 2015–April 2018, according to manufacturers’ protocols at time of study. Clinical characteristics were matched to PD-L1 test results using unique identifiers for the 4714 patients (pts) whose diagnoses and treatment could be determined.

Results: Across tumor types, 56% of pts received a test prior to first-line (1L) Tx. Most lung cancer (57%) or melanoma (MEL; 65%) pts had a PD-L1 test prior to 1L Tx, while most squamous cell carcinoma of the head and neck (70%) or urothelial carcinoma (73%) pts had a PD-L1 test after Tx initiation, in line with drug and complementary Dx approvals for these tumor types during the testing period. The percentage of lung cancer pts whose PD-L1 expression was tested prior to 1L Tx rose from 32% during Q4 2015–Q3 2016 to 63% during Q4 2016–Q1 2018, in line with FDA approval of a companion PD-L1 IHC Dx for non-small cell lung cancer. Regardless of PD-L1 test used, most lung cancer (73%) or MEL (93%) pts received I-O Tx, defined as nivolumab (NIVO; + ipilimumab [IPI] for MEL only), pembrolizumab (pembro) ± chemotherapy, atezolizumab, or IPI alone. Moreover, the majority of lung cancer pts who had ≥1% PD-L1 expression or MEL regardless of PD-L1 expression received 1L I-O Tx irrespective of the PD-L1 test used. Analysis of PD-L1 expression, Dx test used, and Tx received showed that, for MEL pts tested with 22C3, 28%, 17%, and 0% of pts received NIVO or IPI, while 28%, 43%, and 43% received NIVO+IPI, at the expression cutoffs of 0%, 1–49%, and ≥50%, respectively. Lung cancer pts with 1–49% PD-L1 expression, as determined by a 22C3 test, received NIVO or pembro monotherapy at similar rates (12–18%). Of those who had ≥50% PD-L1 expression, as determined by the 28-8 test only, 52% received pembro monotherapy vs other Tx.

Conclusions: Since FDA approval of the first PD-L1 IHC Dx in 2015, analyses of PD-L1 testing practices and physicians’ Tx decision behavior at a US national reference laboratory have shown that physicians’ adoption of PD-L1 testing is responsive to FDA approvals and that most testing for lung cancer and MEL occurs before 1L Tx initiation. In lung cancer or MEL pts who had a PD-L1 test result available, Tx decisions do not appear to be tied to the specific intended use of the PD-L1 assay that was ordered.

Citation Format: Gabriel S. Krigsfeld, Emily Prince, Kim Zerba, Vladislav Chizhevsky, Josette William Ragheb, James White. Real-world utilization of PD-L1 IHC testing and results across multiple tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3993A.