Occult primary parotid gland acinic cell adenocarcinoma presenting with extensive lung metastasis.

Acinic cell adenocarcinoma is a malignant salivary gland neoplasm with a relatively low rate of lymphangitic spread to regional lymph nodes. Distant metastases are rare and their occurrence typically indicates an unfavorable outcome. We encountered an unusual example of acinic cell adenocarcinoma that initially presented in the lung, whereas the primary parotid carcinoma, despite extensive clinical evaluation, only became apparent 1 year after initial diagnosis. The histologic, immunohistochemical, and ultrastructural features of the tumor in the parotid gland and lung were similar. The tumor displayed an aggressive behavior resulting in death within 2 years of the initial presentation. This presentation is unique, showing that peripheral lung tumors of salivary gland type are likely to be metastatic, and careful clinical evaluation is warranted in establishing their primary site of origin.