A case of multiple pulmonary metastasizing pleomorphic adenomas of the salivary gland

To the Editor:As the most common benign neoplasm of the salivary gland,pleomorphic adenoma is characterized by slow progression and low morbidity.[1]It is quite rare for the pleomorphic adenoma to metastasize before undergoing malignant transformation,resulting in that there is no clear consensus about the epidemiology,mechanism of development,treatment,and prognosis of metastasizing pleomorphic adenomas(MPA).[2]According to the systematic review study of James Knight,72.8%of cases reported pleomorphic adenoma(PA)local recurrence before MPA.MPA usually spread to the bone(36.6%),the lung(33.8%),and neck lymph nodes(20.1%).[1]The case we reported was the pulmonary MPA of the salivary gland.