Pulmonary mixed squamous cell and glandular papilloma mimicking adenocarcinoma: a case study and literature review.

Mixed squamous cell and glandular papilloma of the lung is an extremely rare benign neoplasm. Here we present another case of mixed squamous cell and glandular papilloma in a 64-year-old female nonsmoker. Histologically, the tumor was composed of mainly papillary structures covered with squamous, glandular and transitional epithelium. Some glandular structures extending into adjacent bronchiolar and alveolar spaces with mucus were similar to adenocarcinoma. Immunohistochemical analysis showed the different kinds of epithelia had similar immunophenotype. The different components were positive for cytokeratin (CK)7, CK19, CAM5.2, CK5/6, CK34βE12, and TTF-1, but negative for CK20. The transitional morphology and immunohistochemistry indicate the different components likely come from a same kind of progenitor in the bronchiolar wall.