KRT5 and adenocarcinoma: In our LC cohort, 24 tumors (59%) were positive by immunohistochemistry for TTF-1/Napsin A (referred to as adenocarcinoma-like), 5 tumors (12%) were CK5/P40 positive (squamous-like), whereas 12 tumors (29%) did not express any of these IHC markers (marker null cases).