Pulmonary mucoepidermoid carcinoma with prominent tumor-associated lymphoid proliferation.

We report 6 cases of low-grade pulmonary mucoepidermoid carcinoma displaying a striking lymphoplasmacytic infiltrate. All six tumors had a typical pulmonary mucoepidermoid carcinoma presentation as a polypoid endobronchial mass involving the proximal bronchi. The patients were 3 females and 3 males with a mean age of 33 years (range, 5-61 years). Half of the patients were asymptomatic, while half experienced mild symptoms of pneumonia, asthma-like symptoms, or hemoptysis. No tumor-related deaths were observed, with a mean follow-up of 51 months. The tumor size ranged from 2.1 to 3.4 cm (mean, 2.9 cm). The tumors characteristically displayed an elaborate tubulocystic epithelial component composed of intermediate, epidermoid, and mucus-producing cells, and variable numbers of clear cells, multinucleated giant cells, columnar cells, and oncocytic cells. The tumors' lymphoplasmacytic infiltrate with occasional Russell bodies was sufficiently intense to raise concern of a low-grade lymphoma. All tested tumors were immunoreactive with CK7 while nonreactive with TTF-1 and CK20. Recognition of this histologic variant is important for a correct diagnosis of low-grade pulmonary mucoepidermoid carcinoma. The dense lymphoplasmacytic infiltrate is similar to that previously described in salivary glands as tumor-associated lymphoid proliferation.