[Squamous cell carcinoma, basaloid squamous cell carcinoma and adenosquamous carcinoma in the lung]

The precise distinction between adenocarcinoma and squamous cell carcinoma (SqCC) has become very important for determining the appropriate therapy for patients and more specifically to drive the use of tyrosine kinase inhibitors, pemetrexed, anti-VEGF monoclonal antibody and crizotinib. Squamous pearls and distinct intercellular bridges identify keratinizing SqCC. In non-keratinizing SqCC, immuno-histochemistry is required. Recent studies have shown p40 and TTF1 to be the two best markers of SqCC and adenocarcinoma respectively. Many morphological variants of SqCC have been described. Basaloid SqCC is a poorly differentiated epithelial tumor lacking squamous morphology but showing immuno-histochemical expression of squamous makers. The pronostic of basaloid carcinoma is considered poorer than that of other non-small cell lung cancers. Adenosquamous carcinoma shows components of both SqCC and adenocarcinoma. Both components must be clearly identified either on H&E or by immuno-histochemistry. The adenocarcinoma components justified a screening for gene rearrangements. Finally, the recent WHO classification of lung tumors did not change the criteria applying for the grading of preinvasive bronchial lesion.