Subclassification of pulmonary non-small cell lung carcinoma in fine needle aspirates using a limited immunohistochemistry panel

BACKGROUND: Newer treatment modalities require subtyping of non-small cell lung carcinomas (NSCLC). Morphological differentiation is often difficult and various immunohistochemical (IHC) panels have been used to maximize the proportion of accurately subtyped NSCLC. AIM: The aim of this study was to subtype NSCLC on fine needle aspirates (FNA) using a minimal antibody panel. MATERIALS AND METHODS: Cell blocks from 23 FNA samples with a morphological diagnosis of NSCLC were taken. IHC was evaluated (blinded to clinical data) for thyroid transcription factor-1 (TTF-1), cytokeratin (CK)7, CK20, and tumor protein p63. RESULTS: TTF-1 was positive in 14 and negative in 9 cases. The p63 was positive in two cases each of TTF-1 positive and negative tumors. CK7 was positive in 12 of the 14 TTF-1 positive tumors and 4 of the TTF-1 negative tumors. CK20 was negative in all. All the 14 TTF-1 positive tumors were primary lung tumors, 12 being NSCLC and 2 being squamous cell carcinoma. Five of nine TTF-1 negative tumors were metastatic tumors from endometrium, kidney, and head and neck region (two), and one was an unknown primary. Four of the nine TTF-1 negative tumors were morphologically NSCLC and were clinically considered to be primary lung tumors. Three of these tumors stained positive for CK7 but negative for CK20 and p63, and one case was negative for the immunomarkers. CONCLUSION: Use of limited IHC panel helps categorize primary versus secondary tumors to the lung. The p63 is a useful marker for detecting squamous cell carcinoma. In countries where antibodies are not readily available, using a limited IHC panel of TTF-1, p63, and CK7 can help further type NSCLC lung tumors.