Management and outcome of parotid mucoepidermoid carcinoma by histological grade: A 21-year review

Objective Mucoepidermoid carcinoma (MEC) is the most common malignancy of the parotid gland, but the outcome depends on the histological grade. Therefore, the aim of this study was to evaluate MEC on the basis of histological grade. Study Design Retrospective analysis. Methods We performed a retrospective analysis of data from patients whose initial treatment for MEC of the parotid gland was performed at our department between 1999 and 2021. We examined the association between the Armed Forces Institute of Pathology (AFIP) grade and outcome. Results The AFIP grades were as follows: low, 26 cases; intermediate, 9 cases; and high, 31 cases. About 50% of cases were correctly diagnosed as malignant, and both grade and histology were accurately determined by fine-needle aspiration cytology in 20% of cases. The 5-year disease-free survival rate was 95.5% and 53.8% in the low-/intermediate- and high-grade cases, respectively. In the high-grade group, cases with recurrence were found to have a higher rate of lymph nodes metastasis than cases without recurrence. Furthermore, in this high-grade group, total sacrifice of the facial nerve did not reduce local recurrence. However, radical resection in the cases without tumor invasion to the nerve has decreased the local recurrence rate. The CRTC1-MAML2 fusion gene was expressed in 42.3% of low-/intermediate- and 14.3% of high-grade cases. Conclusions The survival rate in MEC was quite different between the low-/intermediate- and high-grade cases. However, the rate of correct assessment of the grade by fine-needle aspiration cytology was poor. In high-grade cases, total sacrifice of the facial nerve may improve the rate of local recurrence in cases without invasion of the main trunk of the nerve. Expression of the CRTC1-MAML2 fusion gene could be helpful in not only the assessment of grade but the prediction of recurrence. Level of Evidence 4

Automated summary

This study found that the histological grade of Mucoepidermoid carcinoma (MEC) is related to prognosis, with a significant difference in survival rate between low/intermediate and high-grade cases. Fine-needle aspiration cytology had a low accuracy in assessing the grade of MEC.