Small cell carcinoma ex-pleomorphic adenoma of the parotid gland

Small cell carcinoma (SCC) is a high-grade malignancy usually encountered in the lungs but also seen in almost any site including the salivary glands. SCC is important to recognize because it often metastasizes widely and is treated with systemic chemotherapy. Carcinoma ex pleomorphic adenoma is a malignant epithelial neoplasm arising in a pre-existing benign mixed tumor (i.e., pleomorphic adenoma, PA). While virtually any salivary carcinoma can arise from a PA, to our knowledge SCC ex-PA has not been described. We report a case of a woman presenting with fullness of the right neck and a parotid gland mass. The tumor was resected and evaluated grossly, by light microscopy, and by immunohistochemistry. Grossly, a 1.6 cm well-circumscribed nodule was identified within the parotid. Microscopic examination revealed foci of SCC associated with high-grade adenocarcinoma, in the background of a PA. The SCC was immunoreactive for cytokeratin in a dot-like pattern and neuroendocrine markers synaptophysin and CD56. Despite the focal nature of the SCC in the parotid, a pure SCC metastasis was present in one neck level II lymph node. The patient was free of disease with 8 months of follow-up. Our case illustrates that: (1) although rare, in the salivary glands SCC may arise from lower grade neoplasms including PAs; (2) SCC ex PA may metastasize as pure SCC even if the primary SCC component was focal; (3) adequate sampling of PAs is crucial to prevent missing a rare SCC that must be treated with chemotherapy.