Mucinous cystadenoma of the lung.

Background: Mucinous cystadenoma is an unusual pulmonary tumor that must be distinguished from mucinous cystic carcinoma and mucinous cystic tumors of borderline malignancy.

Methods: This study of two cases was performed to characterize mucinous cystadenoma clinically and immunohistochemically, using proliferation markers (proliferating cell nuclear antigen [PCNA], MIB1) and carcinoembryonic antigen expression.

Results: Pathologic examination in each instance showed unilocular cysts containing abundant clear mucus. The cysts were lined by tall mucinous epithelium, with absence of cytologic atypia and invasive growth. Proliferation markers using immunohistochemical methods showed less than 10% and 5% of labeled nuclei, respectively. Carcinoembryonic antigen immunostaining in both cases was negative. Patients remained free from recurrence for at least 2 years after surgery.

Conclusions: Mucinous cystadenoma of the lung appears to be a benign neoplasm because of its clinical course and immunohistochemical low expression of proliferation markers such as PCNA and MIB1.