The role of the cytopathologist in subtyping and epidermal growth factor receptor testing in non‐small cell lung cancer: An institutional experience

Objective Approximately 10% of non‐small‐cell lung cancer (NSCLC) remains unclassifiable as NSCLC ‐not otherwise specified ( NOS) , after using a panel of immunomarkers. The present study was undertaken to assess sensitivity and specificity of immunomarkers in sub‐typing NSCLC on fine needle aspiration cytology (FNAC) . Epidermal growth factor receptor (EGFR) mutations were also detected in these samples. Methods Sixty cases of NSCLC including 15 squamous cell carcinoma (SCC) , 15 adenocarcinomas (ADC) and 30 NSCLC ‐ NO S reported on FNAC were included in the study. A panel of CK 7, CK 5/6, TTF ‐1 and p63 was applied in these cases. DNA was extracted from 54 cases including 14 effusion samples, and EGFR mutations were detected. Results Classic ADC cases (n=15) showed 73.3% TTF ‐1 positivity and 100% CK 7 positivity. Two cases of ADC showed aberrant expression of p63 and 2 cases showed CK 5/6 positivity. 80% of classic SCC cases (n=15) showed strong nuclear p63 positivity and 86.6% were positive for CK 5/6. TTF ‐1 was seen exclusively in ADC cases. Immunohistochemistry (IHC) using two immunomarkers ( TTF ‐1 and p63) helped in subtyping 24/30(80%) cases of NSCLC . EGFR mutations were detected in 9/54 (16.7%) cases, and the most common mutation was short in‐frame deletion in Exon 19. Conclusions More than 90% of NSCLC can be sub‐typed on cytology samples with the help of immunochemistry. The sensitivity of TTF ‐1, p63, CK 5/6 and CK 7 was 73.3%, 80%, 100% and 100%, respectively. The specificity of TTF ‐1, p63, CK 5/6 and CK 7 was 100%, 86.6%, 86.6% and 93.3%, respectively. TTF ‐1 is highly specific, and almost 80% of NSCLC ‐ NOS cases can be sub‐typed using TTF ‐1 and p63. EGFR mutations can be detected in cytology samples, and 16.7% samples were positive for EGFR mutations.