NKX2-1 and lung adenocarcinoma: LUSC is characterized for being positive for cytokeratins 5 and 6 (CKs5/6; officially known as KRT5 and KRT6, respectively) as well as for tumor protein p63 (officially known as TP63) and its isoform p40, and for being negative for thyroid transcription factor-1 (TTF1, officially known as TITF1), the pathognomonic immunohistochemical marker of the NSCLC subtype lung adenocarcinoma (LUAD) (Goldstraw et al., 2016).