TTF1 and lung adenocarcinoma: Immunohistochemistry demonstrated strong positivity for thyroid transcription factor-1 (TTF-1) (Figure 2H) and Napsin A (Figure 2I), while negative for ALK(1A4)(routinely performed to exclude ALK-rearranged lung adenocarcinoma, which would impact therapeutic considerations), CK5/6, and P63, confirming primary lung adenocarcinoma.