Metastasis of maxillary sinus adenoid cystic carcinoma to the humerus bone—A rare case report

Adenoid cystic carcinoma accounts for 10 to 12% of all salivary gland malignant neoplasms with an estimated incidence of 3 to 4.5 cases per million per year. Perineural spread and multiple local recurrences are its defining features, although the liver and lung are the most frequent sites for distant metastases. It is extremely uncommon for adenoid cystic carcinoma of the maxillary sinus to spread to distant bones. Few cases of adenoid cystic carcinoma with distant bone metastasis have been reported. Here, we report a known case of the adenoid cystic carcinoma of the maxillary sinus in a 40-yearold male, with isolated metastasis to the left humerus bone presenting 4 years later to the excision of the primary lesion. The fine-needle aspiration cytology, trucut biopsy, and immunocytochemistry of the left humerus osteoexpansile lesion confirmed the diagnosis of metastatic adenoid cystic carcinoma. This rare case report re-emphasizes the distant metastatic potential of adenoid cystic carcinoma.