Diagnostic Utility of CK5/6 and TTF-1 in Subtyping Non-Small Cell Lung Carcinoma: Experience from a Tertiary Care Centre

Introduction: Accurate subtyping of non-small cell lung carcinoma (NSCLC) is essential for therapeutic decision-making. Small biopsies often present diagnostic challenges, making immunohistochemistry (IHC) crucial. This study evaluated the histopathological spectrum and diagnostic utility of CK5/6 and thyroid transcription factor-1 (TTF-1) in NSCLC cases. Materials and Methods: This cross-sectional study was conducted over 18 months in the Department of Pathology, RNT medical college. Sixty-four NSCLC cases diagnosed on histopathology were included. Specimens were processed routinely, stained with Hematoxylin & Eosin, and subjected to IHC for CK5/6 and TTF-1. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Results: Before IHC, SCC, ADC, and NSCLC–NOS accounted for 46.88%, 32.8%, and 20.3% of cases, respectively. After IHC, SCC increased to 62.5%, ADC to 37.5%, and NSCLC–NOS reduced to 0%. CK5/6 showed sensitivity 79.2%, specificity 95%, PPV 90.5%, NPV 88.4% (p < 0.0001). TTF-1 showed sensitivity 75%, specificity 100%, PPV 100%, NPV 70.6% (p < 0.0001). Conclusion: The combined use of CK5/6 and TTF-1 significantly improves NSCLC subclassification, eliminating the NSCLC–NOS category. Routine application in small biopsies can enhance diagnostic accuracy and guide therapy.