Cytohistopathological Association and the Use of a Dual Immunohistochemical Regimen in the Diagnosis of Lung Malignancies: A Cross-sectional Study
Authors: Balasundararajan Uma , John Jaison Jacob , Munavarah Sithy Athiya 
Published: October 2023

Introduction: Lung cancer is a highly aggressive malignancy that causes significant morbidity and mortality. The incidence of lung cancer has been increasing in the past few decades. Cytology aids in the initial evaluation and diagnosis of patients with lung cancer. Currently, the classification of lung carcinoma has expanded beyond small cell lung carcinoma and Non-Small Cell Lung Carcinoma (NSCLC). Precise subtyping of poorly differentiated NSCLC into adenocarcinoma and Squamous Cell Carcinoma (SCC) has a direct impact on patient management and prognosis. The morphologic diagnosis forms the basis and is further supplemented by a panel of immunohistochemical markers. Immunohistochemistry (IHC) is important in cases with poorly differentiated morphology or partial sampling. The IHC panel used includes Tumour Protein p63 (p63) and Thyroid Transcription Factor (TTF1) for subtyping lung cancer. Aim: The present study was conducted with the aim of studying the age and gender distribution, risk factors, cytohistopathological association, and formulating an effective IHC panel for the precise yet effective subtyping of poorly differentiated lung malignancies. Materials and Methods: This cross-sectional study included cases retrieved from the Archives of Pathology Department, SRM Medical College and Research Centre, Chennai, Tamil Nadu, India, between July 2012 and July 2016. The cases included had a diagnosis of lung malignancy (confirmed by cytology/biopsy) or were suspected of having malignancy based on clinical/radiological findings. The study period was from July 2015 to August 2016. The cytology and biopsy slides were reviewed, and the malignancy was classified according to the World Health Organisation (WHO) classification of lung malignancies (2021). IHC was performed on the cases using the markers p63 and TTF1 as a dual regimen. Diagnosis and subtyping of tumours were done based on histomorphology, and the tumours were reclassified based on IHC findings. The data were statistically analysed using SPSS software version 25 and the ROC curve. Results: The mean age of the patients was 60.9 years. The study included a total of 50 cases of lung carcinoma, with an average age of 60.9 years (ranging from 30 to 88 years). Among the cases, 35 (70%) had a positive smoking history. A concordant cytohistopathological association was observed in 26 (52%) of cases. Adenocarcinoma was the predominant subtype, accounting for 21 (42%) of cases. Tumour cells in adenocarcinoma showed positive staining for TTF-1, with the marker exhibiting 100% sensitivity and 83% specificity. In SCC, tumour cells were positive for p63, with the marker demonstrating 92% sensitivity and 82% specificity. Both markers showed effective sensitivity and specificity when used as a dual regimen. Conclusion: Although lung cancer is typically diagnosed in the elderly population, there has been an increase in cases among younger individuals due to urbanisation. Smoking remains an important risk factor for lung malignancy. Exfoliative cytology alone is not sufficient for the diagnosis of lung malignancies and should be supplemented with biopsy for more accurate results. Adenocarcinoma was found to be the most common subtype in our study. The IHC panel of p63 and TTF-1 proved to be an effective regimen for classifying poorly differentiated lung carcinomas.