Most patients are asymptomatic and present with solitary, painless masses. Symptoms include pain, drainage from the ipsilateral ear, dysphagia, trismus, and facial paralysis. (Refer to the PDQ summary on Pain for more information.)
Microscopic grading of mucoepidermoid carcinoma is important to determine the prognosis.[1,12,15] Mucoepidermoid carcinomas are graded as low grade, intermediate grade, and high grade. Grading parameters with point values include the following:
- Intracystic component (+2).
- Neural invasion present (+2).
- Necrosis present (+3).
- Mitosis (≥4 per 10 high-power field [+3]).
- Anaplasia present (+4).
Total point scores are 0 to 4 for low grade, 5 to 6 for intermediate grade, and 7 to 14 for high grade.
In a retrospective review of 243 cases of mucoepidermoid carcinoma of the major salivary glands, a statistically significant correlation was shown between this point-based grading system and outcome for parotid tumors but not for submandibular tumors. Another retrospective study that used this histologic grading system indicated that tumor grade correlated well with prognosis for mucoepidermoid carcinoma of the major salivary glands, excluding submandibular tumors, and minor salivary glands. A modification of this grading system placed more emphasis on features of tumor invasion. Nonetheless, though tumor grade may be useful, stage appears to be a better indicator of prognosis.[3,16]
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.