Best immunohistochemical panel in distinguishing adenocarcinoma from squamous cell carcinoma of lung: Tissue microarray assay in resected lung cancer specimens

The emergence of the targeted therapies for non-small cell lung carcinoma (NSCLC) has generated a need for accurate histologic subtyping of NSCLC. In this study, we assessed the utility of immunohistochemical markers that could be helpful in distinction between adenocarcinoma (ADC) and squamous cell carcinoma (SCC). We performed a battery of immunohistochemistry using tissue microarray for napsin-A, Thyroid transcription factor 1 (TTF-1), p63, cytokeratin (CK) 5/6, thrombomodulin (CD141), Epithelial-related antigen (MOC-31), carcinoembryonic antigen (CEA), Cyclooxygenase 2 (COX-2), high-molecular-weight CK (HMWCK), p27kip1 (p27), and Rb protein in 129 resected primary NSCLC with 81 ADCs and 48 SCCs and 10 metastatic ADC to the lung (primary in colon, 7cases; stomach, 2 cases; vagina, 1 case). Cases of ADC and SCC were morphologically unequivocal and solid tumors with no definite squamous or glandular differentiation were excluded for this analysis. Napsin-A and TTF-1 were positive in 81% and 70% of ADC and in 0% and 2% of SCC, respectively, whereas P63 and CK5/6 were positive in 91% and 90% of SCC and in 9% and 4% of ADC, respectively (P <.001). CD141 stained significantly higher in SCC over ADC (positive in 2% of ADC and 46% of SCC. MOC-31, CEA, COX-2, HMWCK, p27, and Rb appeared to be not useful markers in distinction between ADC and SCC because of their low specificity. None of metastatic ADC to the lung showed positive for napsin-A and TTF-1. It was evident that combination of napsin-A, TTF-1, CK5/6, and p63 was the best immunohistochemical panel in differentiating ADC from SCC of the lung in this study. CD141 appeared to be a potential new marker for SCC with high specificity. Cyclooxygenase 2, MOC-31, CEA, HMWCK, p27, and Rb showed less specificity for differentiation ADC from SCC.