Pulmonary squamous cell carcinoma with lepidic growth pattern: new insights into lung cancer classification

Lung squamous cell carcinoma (SCC) has always been considered a monomorphic entity, different from lung adenocarcinoma which is known to be a very heterogeneous tumor from morphological and molecular point of view. Just two histological subtypes of SCC are recognised, the basaloid and lymphoepithelioma-like histotypes, as in other sites different from the lung. Recently, different studies tried to expand the classification of SCC by adding different subtypes based on morphological characteristics (such as keratinization or clear cell features) or different growth patterns (papillary or basaloid). We report a case of squamous cell carcinoma with a previously unreported, distinctive and predominant “lepidic” growth pattern, with its immunophenotypical and molecular characterization.