Significance of Immunohistochemistry Testing in the Diagnosis and Subtyping of Lung Carcinomas- A Retrospective Study from a Tertiary Care Centre in Southern Rajasthan

Introduction: In the present era, the classification of lung carcinoma is not confined to Small Cell Lung Carcinoma (SCLC) and Non Small Cell Lung Carcinoma (NSCLC). Precise subtyping of lung carcinoma has a direct impact on patient management and prognosis. Further molecular study helps in identifying adenocarcinoma receptors, such as Epidermal Growth Factor Receptor (EGFR) and Anaplastic Lymphoma Kinase (ALK), which are useful in targeted therapy. Aim: To assess the role of Immunohistochemistry (IHC) in accurate diagnosis and subtyping of lung carcinoma and to analyse the prevalence of EGFR mutations and ALK rearrangement in lung adenocarcinoma. Materials and Methods: A retrospective hospital-based, observational study was conducted at the Department of Pathology of American International Institute of Medical Sciences, Udaipur, Rajasthan from January 2020 to August 2021. Total of 105 cases of guided core needle biopsies from lung and bronchoscopic biopsies were included. IHC markers were applied based on histopathological diagnosis from a panel of p63, Cytokeratin 7 (CK7), AE1/AE3, Thyroid Transcription Factor (TTF1), Napsin A, p40, synaptophysin, chromogranin, CD56 and Ki67. Adenocarcinoma cases were further analysed for EGFR mutations and ALK rearrangements. Data was tabulated and analysed statistically using Microsoft Excel to determine the percentage frequency distribution of cases. Results: Among 105, there were 88 males and 17 females and the mean age of the population was 60.57 years. The most prevalent subtype of lung malignancy was squamous cell carcinoma (44.7%) followed by adenocarcinoma (29.5%). The diagnostic accuracy of squamous cell carcinomas and adenocarcinomas on morphology was 93.1% and 84.6%, respectively and for small cell carcinoma it was 100%. Amongst 28 cases of adenocarcinoma, EGFR mutation was found in 46.42% cases whereas ALK mutation was found only in 21.42% cases. Conclusion: The study highlights the importance of IHC, and a substantial prevalence of EGFR mutations was found in patients with lung carcinoma.