P1.09-01 PD-L1 Testing On NSCLC Cytology Samples in a UK Teaching Hospital

Immunotherapy, specifically pembrolizumab, is now approved in the UK as first-line therapy in patients with advanced non-small cell lung cancer (NSCLC) and no activating EGFR mutation or ALK translocation if high PD-L1 expression (≥50%) can be demonstrated on tumour samples. Furthermore, second line treatment is approved with PD-L1 expression ≥1%. Initial studies were performed exclusively on histological samples. We present our experience of PD-L1 testing purely on cytology samples. Prospectively maintained cytology databases were analysed to identify all lung cancer cytology samples from our institute tested for PD-L1 expression between January 2017 and March 2018. Cell blocks from endo-bronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) performed using rapid on-site evaluation (ROSE), FNA of other sites, pleural fluid and bronchial brush samples were prepared and immunohistochemistry performed on sections using the Dako 22c3 antibody to determine PD-L1 expression. A total of 99 samples were tested for PD-L1. There was sufficient material for PD-L1 testing in 95% (n=94). Male 62%, female 38%, age range 26-84. EBUS-TBNA accounted for 79% of samples, percutaneous Fine Needle Aspirate (FNA) 11%, pleural fluid samples 7%, bronchial brush 2% and endoscopic ultrasound FNA 1%. Table-1 provides a breakdown of the methods of sample acquisition with adequacy rates and PD-L1 expression. Overall PD-L1 expression was highly (≥50%) positive in 34/94 (36%), low (≥1-50%) positive in 38/94 (40%), and negative in 22/94 (23%). The proportion of patients expressing high (≥50%) PD-L1 positivity in the different pathological subtypes were: adenocarcinoma 23/62 (37%), squamous cell carcinoma 8/21 (38%), NSCLC-NOS 3/9 (33%). The proportion of patients with low (≥1-50%) PD-L1 positivity were: adenocarcinoma 27/62 (44%), squamous cell carcinoma 9/21 (43%), NSCLC-NOS 2/9 (22%). Neither of 2 neuroendocrine NSCLC tested expressed PD-L1 Our experience demonstrates that cytological samples obtained at our institute are suitable for PD-L1 testing with an adequacy rate of 95%.