Cytogenetically, mucoepidermoid carcinoma is characterized by a t(11;19)(q14–21;p12–13) translocation, which is occasionally the sole cytogenetic alteration.[17,18,19] This translocation creates a novel fusion product, MECT1-MAML2, which disrupts a Notch signaling pathway. Notch signaling plays a key role in the normal development of many tissues and cell types, through diverse effects on cellular differentiation, survival, and/or proliferation, and may be involved in a wide variety of human neoplasms.
Rarely, mucoepidermoid carcinoma may originate within the jaws. This tumor type is known as central mucoepidermoid carcinoma. The mandibular to maxillary predilection is approximately 3:1.
Adenoid cystic carcinoma
Adenoid cystic carcinoma, formerly known as cylindroma, is a slow growing but aggressive neoplasm with a remarkable capacity for recurrence. Morphologically, three growth patterns have been described: cribriform, or classic pattern; tubular; and solid, or basaloid pattern. The tumors are categorized according to the predominant pattern.[3,23,24,25] The cribriform pattern shows epithelial cell nests that form cylindrical patterns. The lumina of these spaces contain periodic acid-Schiff (PAS)-positive mucopolysaccharide secretions. The tubular pattern reveals tubular structures that are lined by stratified cuboidal epithelium. The solid pattern shows solid groups of cuboidal cells. The cribriform pattern is the most common, and the solid pattern is the least common. Solid adenoid cystic carcinoma is a high-grade lesion with reported recurrence rates of as much as 100% compared with 50% to 80% for the tubular and cribriform variants.
In a review of its case files, the AFIP found adenoid cystic carcinoma to be the fifth most common malignant epithelial tumor of the salivary glands after mucoepidermoid carcinomas; adenocarcinomas, NOS; acinic cell carcinomas; and PLGA. Other series, however, report adenoid cystic carcinoma to be the second most common malignant tumor with an incidence or relative frequency of approximately 20%. In the AFIP data, this neoplasm constitutes approximately 7.5% of all epithelial malignancies and 4% of all benign and malignant epithelial salivary gland tumors. The peak incidence for this tumor is reported to be in the fourth through sixth decades of life.
This neoplasm typically develops as a slow growing swelling in the preauricular or submandibular region. Pain and facial paralysis develop frequently during the course of the disease and are likely related to the associated high incidence of nerve invasion. (Refer to the PDQ summary on Pain for more information.) Regardless of histologic grade, adenoid cystic carcinomas, with their unusually slow biologic growth, tend to have a protracted course and ultimately a poor outcome, with a 10-year survival reported to be less than 50% for all grades.[1,27] These carcinomas typically show frequent recurrences and late distant metastases.[1,28] Clinical stage may be a better prognostic indicator than histologic grade.[28,29] In a retrospective review of 92 cases, a tumor size larger than 4 cm was associated with an unfavorable clinical course in all cases.