A Minimal Immunohistochemical Panel for Subtyping Poorly Differentiated Non-Small Cell Lung Carcinoma: A Tissue Microarray Study Simulating Small Biopsy Conditions

ABSTRACT

PURPOSE: Given the emerging evidence for differential responses to new targeted therapies and the identification of molecular differences between specific subtypes of non-small cell lung carcinoma (NSCLC), there is an increased need for greater accuracy in subtyping NSCLC. In a substantial proportion of cases, standard morphology cannot specifically subtype the tumor, resulting in a final diagnosis of NSCLC-not otherwise specified. In this study, we added newly proposed markers (napsin A, desmocollin-3) to conventional markers (p63, thyroid transcription factor-1 [TTF-1], cytokeratin 5/6 [CK5/6], high molecular weight cytokeratin [HMWCK], cytokeratin 7 [CK7]) and evaluated for the minimal panel of immunohistochemical markers required for subtyping poorly differentiated (PD) NSCLC. MATERIALS AND METHODS: Resection specimens of 110 adenocarcinomas (ADCs) and 171 squamous cell carcinomas (SCCs) were collected and tissue microarrays were constructed to simulate small biopsy conditions. All specimens were stained with TTF-1, napsin A, CK7, p63, CK5/6, HMWCK, desmocollin-3 and mucicarmine. RESULTS: For 32 PD ADC, a combination of TTF-1 and napsin A increased sensitivity (81%). With regard to the 29 PD SCC, a combination of desmocollin-3 and p63 did not substantially increase diagnostic performance. Logistic regression analysis identified napsin A, p63 and TTF-1 as the optimal panel to separate PD ADC and PD SCC. Mucin stains for PD NSCLC increased accuracy rate (88%) for diagnosis of PD ADC. CONCLUSION: We recommend a minimal panel of immunohistochemical and histochemical markers to include TTF-1, p63, napsin A and one of mucin stains for tumor subtyping of PD NSCLC in a small biopsy sample.