Background: The expression levels of Programmed death ligand-1 (PD-L1), epidermal growth factor receptor (EGFR), anaplastic lymphoma tyrosine kinase gene (ALK), and proto-oncogene tyrosineprotein kinase 1 ROS (ROS1) are important for targeted treatment selection in advanced lung cancer. Most patients with lung cancer are diagnosed at an advanced stage and have no chance of surgery. For this reason, the accuracy and reliability of cytology samples for detecting those markers is important in patients whose histological sampling cannot be performed.
Aims: To test the compatibility of histological and cytological sample analysis results of EGFR, ALK, ROS1 and PDL-1 in patients with NSCLC and to determine the adequacy of cytological analysis for PD-L1 expression.
Study design: Retrospective cross-sectional study.
Methods: The results of 231 patients whose PD-L1 was studied in 2018 were analyzed retrospectively. We excluded 11 inappropriate samples. A total of 220 samples were distributed as follows; 66 (30.0%) cytology specimens, 64 (29.1%) small histology biopsies, and 90 (40.9%) surgical biopsies. EGFR, ALK, ROS1 and PD-L1 analysis were performed in 139, 134, 116, and 220 patients, respectively. Samples containing >400 cells were considered suitable for molecular cytological study.
Results: A total of 154 (70.0%) histological (surgical biopsy) and 66 (30.0%) cytology samples were analyzed. There was no statistically significant difference between histological and cytological samples in terms of cellular adequacy for all molecular markers [EGFR: 93.7% and 90.9% (P = .556), ALK: 97.8% and 95.3% (P = .436) , ROS1: 89.9% vs. 91.9% (P = .729), PD-L1: 95.5% vs. 92.4% (P = .364)]. There was no statistically significant difference in the expression positivity rates of all biomarkers between histological and cytological samples [EGFR: 9.0% vs. 2.5% (P = .018), ALK: 7.9% vs. 9.8% (P = .719), ROS1 : 1.4% vs. 2.9% (P = .591), PD-L1: 54.4% vs. 41.0% (P = .078)].
Conclusion: The cellular adequacy of cytology specimens for molecular testing in patients with NSCLC is satisfactory. This study shows that EGFR, ALK, ROS-1 and PDL-1 expression rates in cytological samples are not statistically different from histological samples.