Low-grade mucoepidermoid carcinoma with regional lymph node metastasis: A case report and genetic review of criteria for grading

Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy. It accounts for 5% of all salivary gland tumors and 20% of salivary malignancies and has various clinical outcomes. Its prognosis is related to the tumor grade in the WHO classification of head and neck tumors. MEC is divided into high, intermediate and low grades. In general, low-grade MEC with cervical lymph node metastasis is rare, and primary MEC that occurs in a minor salivary gland with cervical lymph node metastasis is very rare. Low-grade lesions have quite different behavior from high-grade ones, leading to differences in the treatment course required for disease control. MEC is associated with recurring chromosomal translocation t(11;19)(q21;p13). CRTC1-MAML2 gene fusion was identified from the recurring translocation, which is often the sole cytogenetic alteration in this disease. This fusion transcript is detected frequently in MEC and is involved in the transformation of epithelial cells. Detection of the CRTC1-MAML2 fusion transcript is associated with a less advanced clinical stage and low-grade tumor histology. The presence of the transcript is associated with longer disease-free and overall survival periods. Here, we report a rare case of low-grade MEC with cervical lymph node metastasis. The findings for this patient show that the CRTC1-MAML2 fusion transcript may be specific to MEC, and associated with a distinct MEC subset that exhibits favorable clinicopathologic features.