Cell‐blocks are suitable material for programmed cell death ligand‐1 immunohistochemistry: Comparison of cell‐blocks and matched surgical resection specimens in lung cancer

OBJECTIVE: Programmed cell death ligand‐1 (PD‐L1) has emerged as a predictive biomarker in lung cancer. PD‐L1 immunohistochemistry (IHC) assay predicts the response to immunotherapy, but cytology specimens are often the only samples available in a considerable proportion of advanced lung cancer patients. We delineate practical feasibility and efficacy of cytology cell‐block (CB) specimens for PD‐L1 expression and concordance between cytology CBs and surgical resection specimens. METHODS: In total, 58 eligible patients with primary lung cancer who received computed tomography‐guided percutaneous needle aspiration and surgery were included. PD‐L1 IHC (clone SP263) was performed on CBs prepared from residual liquid‐based cytology material and matched surgical resection specimens. PD‐L1 positive tumour cell proportion was categorised in four score groups: (a) <1%; (b) ≤1% to <10%; (c) ≤10% to <50%, (d) ≥50%. RESULTS: Comparison of PD‐L1 expression in cytology CBs and matched surgical resection specimens showed a high concordance (κ value 0.65). According to the therapeutic guideline of immunotherapeutic agents, a positive percent agreement was 94.34%, and a negative percent agreement was 100% at a cut‐off value for positivity of 1% PD‐L1 expression. There was a significant difference observed with regard to rates of PD‐L1 positivity when comparing smoking history (P = 0.02), age (P = 0.04) and pathological TNM stage (P = 0.04). CONCLUSIONS: The results show that cytology CBs evaluated for PD‐L1 IHC assay have high concordance with matched surgical resection specimens and can be used for assessing PD‐L1 expression. Also, we propose that CBs are suitable materials for evaluating PD‐L1 expression while simultaneously performing both diagnostic and molecular tests.