Salivary duct carcinoma
Salivary duct carcinoma, also known as salivary duct adenocarcinoma, is a rare, typically high-grade malignant epithelial neoplasm composed of structures that resemble expanded salivary gland ducts. A low-grade variant exists. Incidence rates vary depending upon the study cited. In the AFIP files, salivary duct carcinomas represent only 0.2% of all epithelial salivary gland neoplasms. More than 85% of cases involve the parotid gland and approximately 75% of patients are men. The peak incidence is reported to be in the seventh and eighth decades of life.
Clinically, parotid swelling is the most common sign. Facial nerve dysfunction or paralysis occur in more than 25% of patients and may be the initial manifestation. The high-grade variant of this neoplasm is one of the most aggressive types of salivary gland carcinoma and is typified by local invasion, lymphatic and hematogenous spread, and poor prognosis.[3,7] In a retrospective review of 104 cases, 33% of patients developed local recurrence, and 46% of patients developed distant metastasis.
Mucinous adenocarcinoma is a rare malignant neoplasm characterized by large amounts of extracellular epithelial mucin that contains cords, nests, and solitary epithelial cells. The incidence is unknown. Limited data indicate that most, if not all, occur in the major salivary glands with the submandibular gland as the predominant site.[3,49] These tumors may be associated with dull pain and tenderness.[3,49] This neoplasm may be considered to be low grade.
Malignant mixed tumors
The classification of malignant mixed tumors, includes three distinct clinicopathologic entities: carcinoma ex pleomorphic adenoma, carcinosarcoma, and metastasizing mixed tumor. Carcinoma ex pleomorphic adenoma constitutes the vast majority of cases, whereas carcinosarcoma, a true malignant mixed tumor, and metastasizing mixed tumor are extremely rare.
Carcinoma ex pleomorphic adenoma
Carcinoma ex pleomorphic adenoma, also known as carcinoma ex mixed tumor, is a carcinoma that shows histologic evidence of arising from or in a benign pleomorphic adenoma. Diagnosis requires the identification of benign tumor in the tissue sample. The incidence or relative frequency of this tumor varies considerably depending on the study cited. A review of material at the AFIP showed carcinoma ex pleomorphic adenoma to comprise 8.8% of all mixed tumors and 4.6% of all malignant salivary gland tumors, ranking it as the sixth most common malignant salivary gland tumor after mucoepidermoid carcinoma; adenocarcinoma, NOS; acinic cell carcinoma; polymorphous low-grade adenocarcinoma; and adenoid cystic carcinoma. The neoplasm occurs primarily in the major salivary glands.
The most common clinical presentation is a painless mass. Approximately 33% of patients may experience facial paralysis. Depending on the series cited, survival times vary significantly: 25% to 65% at 5 years, 24% to 50% at 10 years, 10% to 35% at 15 years, and 0% to 38% at 20 years. In addition to tumor stage, histologic grade and degree of invasion are important parameters to determine prognosis.