Mucoepidermoid carcinoma of salivary glands: a study of 69 cases with special attention to histologic grading.

Sixty-nine cases of mucoepidermoid carcinoma with a minimum of five years follow-up are presented. Major salivary glands were involved in 46 cases (44 parotid, two submandibular), and intraoral minor glands in 23. The tumor was considered histologically high grade (20 cases) when 90% or more of its area was made up of tumor cells and 10% or less of intracystic space and low grade (49 cases) when this ratio was lower. The proportion of cell types was not considered in grading: although intermediate, epidermoid, and clear cells usually predominated in high-grade tumors, several such examples contained numerous mucous cells. Grade was highly significant prognostically; all but 2 of the 14 deaths due to tumor and all six instances of distant metastasis occurred in cases with high-grade tumors. High histologic grade also was associated with an increased incidence of local recurrence (particularly recurrence not subsequently controlled) and cervical lymph node metastasis; in the case of recurrence this was due in part to the fact that inadequate surgical margins were more common with high-grade tumors. Tumors measuring less than 2.5 cm were rarely fatal regardless of grade, there being only two such deaths (one high grade, one low grade). Nuclear anisochromia and pleomorphism of more than slight degree, frequent mitoses, and tumor necrosis of more than focal extent were found to be untypical of mucoepidermoid carcinoma regardless of grade; these findings should occasion consideration of other diagnoses such as poorly differentiated adenocarcinoma with a solid growth pattern and adenosquamous carcinoma.