A case of salivary gland-type mixed tumor of the lung differentiating toward type II alveolar epithelial cells in glandular components with a literature review

Salivary gland-type mixed tumor primarily arising in the lung is extremely rare. We report here a case of this type of tumor that occurred in the periphery of S4 of the right middle lobe in a 74-year-old man. Light-microscopically, this lung tumor, 15x9mm in size, exhibited almost the same features as those of mixed tumor of the salivary gland intermingled with chondromyxoid stroma, glandular component, solid growth pattern of myoepithelial components and well-developed cartilage formation, exhibiting a sharp margin. Immunohistochemical study revealed that the glandular components in the tumor was positive for thyroid transcription factor-1, TTF-1, a marker of epithelial cells of the thyroid as well as the lung. Furthermore, surface lining cells of the glandular components and luminal contents were positive for surfactant apoprotein A, PE-10, used as a marker of type II alveolar epithelial cells. These findings clearly demonstrate for the first time that glandular epithelial cells in the present salivary gland-type mixed tumor exhibited differentiation toward type II alveolar epithelial cells.