Abstract 5530: PD-L1 expression in patients screened for phase 2 head and neck squamous cell carcinoma clinical studies (HAWK and CONDOR)

PD-L1 expression by immunohistochemistry (IHC) has proven to be a useful biomarker in determining patient response to anti-PD-1/PD-L1-directed therapeutics in several cancers, including HNSCC. Understanding the impact of sample type and demography on PD-L1 expression will inform the suitability of tumor biopsies for testing. Patients entering the HAWK and CONDOR studies were screened for PD-L1 expression (n=669) in a tumor tissue sample using the Ventana PD-L1 SP263 IHC assay as part of the inclusion criteria. PD-L1 assessment was performed centrally using fully validated test procedures and scoring by trained pathologists. Patients were classified as PD-L1 high if ≥25% of tumor cells (TCs) showed membrane staining. Recently acquired or archival samples ≤3 years old were permitted. Baseline demographic and clinical factors were obtained from the clinical database. Prevalence of PD-L1 expression was assessed according to various clinical and demographic characteristics, sample type (biopsy or resection) and location of biopsy (primary tumor vs metastatic site). Comparisons of PD-L1 expression between subgroups of samples were undertaken using a test for equality of proportions. PD-L1 prevalence was significantly higher in females, patients who never smoked, and those with oral cavity primary. Prevalence was similar in archival and recently acquired samples, by HPV status, and between primary and metastatic sites and for biopsies compared with resections (Table). A separate internal study using 40 pairs of matched samples from a commercial source confirmed strong concordance in PD-L1 status between primary and metastatic sites. These results indicate that various sample types can be reliably used for the determination of TC PD-L1 status in HNSCC. Similar prevalence of PD-L1 expression was found between primary and metastatic lesions and archival compared to recently acquired tissue, with important implications in everyday clinical practice. Table % patients with tumor cell PD-L1 ≥25% (n)P ValueSexMale Female24.5% (534) 36.3% (135)0.00817EthnicityAsian Black/African American White23.8% (21) 20.7% (29) 28.7% (561)0.584Age>65 ≤6524.0% (183) 28.0% (486)0.354Smoking status*Current smoker Ex-smoker Never smoked20.8% (48) 24.1% (245) 50.0% (86)1.27e-05Disease classification*Locally advanced Metastatic28.9% (135) 29.9% (244)0.926HPV status*HPV+ HPV-29.3% (116) 26.9% (242)0.720WHO status at baseline*Normal activity Restricted activity29.6% (115) 29.3% (263)>0.999Site