The histological type is defined based on cell morphology, however when there is a lack of differentiation evidences, immunohistochemistry is performed using adenoma or squamous carcinoma markers: trefoil factor-1 (TTF-1), cytokeratin-7 (CK-7) and napsin-A (ASP4; LUAD); interleukin-9 (IL-9 or p40) and cytokeratin-5/6 (CK-5/6; LUSC) [38,39]. Here, KRT5 is linked to squamous cell carcinoma.