Mucinous adenocarcinoma is a rare malignant neoplasm characterized by a large amount of extracellular epithelial mucin. In the present report, an extremely rare case of a mucinous adenocarcinoma in a minor salivary gland of the upper lip is described, along with a brief discussion. A 82-year-old woman was referred to our department because of a swelling on the left side of the upper lip on May 20, 2004. She noticed the swelling in September 2003. Physical examination revealed a painless nodule, measuringl4×12mm, on the mucosal side of the lip. The nodule felt elastic, firm, and movable. The skin was intact, without tumor invasion. There was no lymphadenopathy palpable in cervical region. Ultrasonography revealed a homogenous hypoechoic tumor with an illdefined margin. On the basis of these findings, a clinical diagnosis of a tumor in the upper lip was made, and excisional biopsy was performed on June 3, 2004. Histopathological examination showed a malignant neoplasm with characteristics indicating mucin production. A metastatic tumor was thus suspected. Therefore, the patient was examined by taking a detailed history and performing radiography and scintigraphy. However, no malignancy was detected in any other organs. Because subsequent histopathological examination revealed signs of residual tumor cells at the resection margin, additional excision of the tumor and skin was planned under general anesthesia. The postoperative course was uneventful. Histopathologically, the tumor was composed of glandular neoplastic cells that produced a large amount of mucin. Nests, cords, sheets, and clusters of neoplastic cells were found floating in mucin pools separated by fibrous connective tissue bands. The final diagnosis was a mucinous adenocarcinoma of the upper lip.
