Prognostic features in mucoepidermoid carcinoma of major salivary glands with emphasis on tumour histologic grading

AimsTo compare the different grading systems of mucoepidermoid carcinoma (MEC) and identify the most reliable and objective histopathologic features predictive of outcome. Methods and resultsSeventy-two cases diagnosed as MEC were subjected to a meticulous histopathologic re-review. 20 of 72 (28%) cases were originally misdiagnosed as MEC including 16 as high grade (HG). Among the 52 confirmed MEC, median follow up (FU) was 59months. Mitosis (4/10 High Power Fields), necrosis, pleomorphism, focal keratinization, desmoplasia, and lymph node metastasis were associated with adverse disease specific survival (DSS) and recurrence free survival (RFS) (P<0.002). In all grading systems, low and intermediate grade had similar DSS and RFS but much better outcome than HG (P<0.007). All patients with tumour harboring low mitotic rate and no necrosis did not recur except for one patient with a positive margin. All cases with high mitotic rate and necrosis died or recurred. ConclusionsThe majority of previously diagnosed HG MEC cases are misclassified. There is no difference in outcome between low and intermediate grade in all grading schemes. Consideration should be given to stratify MEC based on relatively objective criteria such as mitosis and necrosis.