Clinico-Pathological Profile of Non-Small Cell Lung Carcinoma with Emphasis on Diagnostic Immunohistochemistry – An Institutional Experience

Background: Non-small cell lung carcinoma (NSCLC) is a heterogeneous group of lung cancers, representing the most prevalent subtype, accounting for at least 85% to 90% of all cases. Given the diversity of its histopathological subtypes, accurate diagnosis, and classification are essential for appropriate treatment planning. Immunohistochemistry aids in distinguishing NSCLC subtypes, as well as helps in identifying actionable mutations and protein expression patterns for targeted therapeutic strategies. Objective: By analysing a cohort of NSCLC, this study aims to profile the clinical and pathological characteristics of NSCLC, with special emphasis on assessing the utility of immunohistochemical correlation (IHC) markers in accurately differentiating between subtypes and confirming the diagnosis, thereby underscoring its value in clinical practice. Materials and Methods: We conducted a retrospective study on NSCLC patients diagnosed via biopsy/resection from February 1, 2016, to August 15, 2019, at a South Indian tertiary care hospital. We analysed clinical details and histopathological features and subtyped them using IHC markers (TTF-1, Napsin A, p40, p63) according to IASLC/ATS/ERS classification. We evaluated IHC sensitivity, specificity, and its impact on treatment decisions. Results: Out of 208 patients, 73.6% were male and 26.4% female. Adenocarcinoma (ADC) (52.8%) was the most common subtype, followed by squamous cell carcinoma (SCC) (35.5%), NSCLC, not otherwise specified (NOS) (9.6%), and one mucoepidermoid case. Most SCC were found in male smokers with chronic obstructive pulmonary disease (COPD). IHC analysis was performed on 135 patients. Of the 49 cases diagnosed morphologically as adenocarcinomas, 47 were confirmed on IHC. Two were categorised as NSCLC, NOS on IHC. Of the 72 cases demonstrating squamoid morphology, 45 were confirmed to be SCC by IHC. Twenty-one of the 72 were diagnosed as adenocarcinomas and six as NSCLC, NOS based on IHC. Conclusion: This study highlights the critical importance of IHC in the diagnostic workup of NSCLC. IHC significantly enhances the accuracy of NSCLC diagnosis, particularly in ambiguous cases. Therefore, integrating IHC into routine diagnostic protocols improves precision and supports effective treatment planning, thereby optimizing patient outcomes.