TTF-1 is a member of the NKX2 family of homeodomain transcription factors found in epithelial cells of the thyroid gland and lung. TTF-1 has been shown to stain approximately 65-70% of cases of lung adenocarcinomas (ADC), with a small number of cases of lung squamous cell carcinoma (SCC) also positive for TTF-1 (1-4).
Napsin A is an aspartic proteinase expressed in type II pneumocytes and in adenocarcinomas of the lung (1). Napsin A has been found to be a sensitive and specific marker of lung ADC. Napsin A has been shown to positively stain 85-90% of cases of lung ADC, while negative staining has been observed in nearly all cases of lung SCC (1-6).
The antibody cocktail of TTF-1 + Napsin A has demonstrated a sensitivity of 91% (105/115) for lung ADC and 95% specificity (5/95) versus lung SCC (2). In cases where TTF-1 and Napsin A are both positive, specificity versus lung squamous cell carcinoma has been shown to be 100% (2).