A prospective observational study to assess PD-L1 expression in small biopsy samples for non-small-cell lung cancer

Programmed cell death-1 (PD-1) immune checkpoint inhibitor antibody has proven to be effective in advanced non-small cell lung cancer (NSCLC) patients positive for programmed cell death-1 ligand-1 (PD-L1). However, there are currently no prospective studies evaluating PD-L1 expression for small biopsy samples.

To prospectively investigate the reliability of small samples for NSCLC, we included patients who underwent diagnostic biopsy by flexible bronchoscopy, computed tomography (CT) and ultra-sonography (US) guided core-needle to determine the PD-L1 expression status. In pathologically confirmed NSCLC, PD-L1 expression was evaluated using companion diagnostic PD-L1 immunohistochemistry. We evaluated: 1) tumor cell count and sample size, 2) tumor proportion score (TPS): <1, 1-49%, 50%≦, and 3) the concordance rate of TPS by biopsy and surgical samples.

Of the 153 cases of PD-L1 expression, 110 were assessed using endobronchial ultrasonography guided transbronchial biopsy (EBUS-TBB) (thin bronchoscopy 84 cases; normal bronchoscopy 26 cases), 23 were endobronchial ultrasonography guided transbronchial needle aspiration (EBUS-TBNA), and 20 cases of CT or US-guided core-needle biopsy. Tumor cell count and sample size were significantly larger for normal bronchoscopy than thin bronchoscopy or EBUS-TBNA samples. Moreover, tumor cell counts for each subsequent biopsy decreased. In all cases, TPS distribution (undiagnosed, <1%, 1-49, 50%≦) was 2.6, 34.6, 31.4, 31.4%, respectively. TPS positive cases using thin bronchoscope was 55.9%, normal bronchoscope was 73.1% and EBUS-TBNA was 78.3%. In early stage adenocarcinoma, TPS was lower compared with advanced stages. Conversely, in squamous cell carcinoma, the rates of TPS were similar regardless of stage. The concordance rate of TPS by biopsy and surgical materials was 86.7%.

Utilizing smaller samples for evaluation, the frequency of TPS was comparable to past clinical trials using larger samples. The differences in TPS were influenced by diagnostic tools, cancer histologic types and staging. The concordance of TPS between EBUS-TBB samples and surgical materials was high.

This study was performed at the Department of Respiratory Medicine at St. Marianna University School of Medicine Hospital, with ethics approval (#3590) and registered as a clinical trial ( UMIN000027030 ).