Dual color multiplex TTF-1 + Napsin A and p63 + CK5 immunostaining for subcategorizing of poorly differentiated pulmonary non-small carcinomas into adenocarcinoma and squamous cell carcinoma in fine needle aspiration specimens

BACKGROUND: The distinction of lung adenocarcinoma (ADC) from squamous cell carcinoma (SCC) has important therapeutic implications. Napsin A is a recently developed marker, which has shown high specificity for lung tissue in the surgical pathology specimens. In this study, we have evaluated whether the use of a panel of novel multiplex cocktails of TTF-1 + Napsin A and p63 + CK5 for dual color immunostaining will improve the diagnostic accuracy of lung adenocarcinoma and squamous cell carcinoma in fine needle aspiration (FNA) specimens, usually with relatively scant microfragments of diagnostic material. MATERIALS AND METHODS: Formalin-fixed, paraffin-embedded, adequately cellular FNA cell blocks with a confirmed diagnosis of either ADC (n = 22), SCC (n = 20) or poorly differentiated carcinoma (PDC; n = 7), from a total of 49 consecutive cases, were studied. All these cases had subsequently confirmed diagnosis in biopsies or resection specimens. The sections were immunostained with two color methods of TTF-1 + Napsin A and p63 + CK5 multiplex cocktails. The presence of one or more unequivocal individual tumor cells with convincing brown nuclear TTF-1 and red cytoplasmic Napsin A staining, and cells with brown nuclear p63 and membranous / cytoplasmic CK5 staining were interpreted as ‘positive’. RESULTS: All 20 FNA cell blocks from SCC cases were positive for dual stain p63 + CK5 and negative for dual stain TTF-1 + Napsin A. The sensitivity and specificity of the dual immunoexpressions of p63 + CK5 for SCC of lung FNAs were both 100%. All 22 ADC cases were positive with dual stain of TTF-1 + Napsin A and negative for dual stain of p63 + CK5. On follow-up of the surgical pathology specimens, 22 cases were confirmed as ADC. The sensitivity of the dual immunoexpression of TTF-1 + Napsin A for ADC of lung FNAs was 100% and the specificity was also 100%. Of the seven PDC cases, five cases that were positive for dual stain p63 + CK5 and negative for dual stain TTF-1 + Napsin A could be categorized as SCC. Two of the seven (2 / 7) PDC cases were positive for dual stain TTF-1 + Napsin A and negative for dual stain p63 + CK5, consistent with ADC. CONCLUSIONS: Simultaneous coordinate or individual immunostaining for Napsin A / TTF-1 in ADC and p63 / CK5 in SCC demonstrated high sensitivity and specificity. The panel with multiplex Napsin A / TTF-1 and p63 / CK5 dual color immunostains could specifically subcategorize PDC into ADC and SCC in lung FNA specimens. Multiplex dual color Napsin A / TTF-1 and p63 / CK5 immunostaining is especially recommended for evaluation of FNA specimens with relatively scant cellularity.