Metastasizing Pleomorphic Adenoma as a subcutaneous mass

Summary: Metastasizing pleomorphic adenoma is a rare subtype indistinguishable from the primary tumor, that occurs after multiple recurrences and must be distinguished from malignancy. Metastases are most commonly seen in bone, lung, and neck lymph nodes. We report a case of a 33- year-old female with a remote history of pleomorphic adenoma of the left submandibular gland for which she has undergone submandibular gland excision 15 years ago. She noted recurrent swelling in her left neck and CT scan which showed multiple nodules in the left neck. Core biopsy showed a pleomorphic adenoma. Patient had a left modified radical neck dissection. Grossly, the specimen was yellow lobulated fatty tissue with multiple lymph nodes/tumor deposits. Microscopically, the lesion consists of multiple, discrete round nodules of variable sizes, with admixture of bilayered ducts, myoepithelial cells, and chondromyxoid/fibrous stroma in the absence of invasion and cytomorphological malignant features. Additional sections to fully submit the fatty tissue was performed and no malignant cytomorphological features was identified. Patient was referred radiation oncology to discuss possible adjuvant treatment. Metastasizing pleomorphic adenoma is histologically and molecularly indistinguishable from a benign tumor at a primary location. No histologic or molecular features can reliably predict metastasis.