TTF1 and renal cell carcinoma: In our study, we found that 47.5% of clear cell RCCs were positive for Napsina A. When dealing with a tumor in the lung if the differential diagnosis includes lung adenocarcinoma versus renal cell carcinoma including clear cell RCC, IHC for TTF-1, PAX-8, and vimentin in addition to napsin A may be helpful.