Mucoepidermoid Carcinoma of Tracheobronchial Tree: Clinicopathological Study of 31 Cases

Background: All aspects of mucoepidermoid carcinoma (MEC) of the lung including histologic grading, clinical behavior and its differentiation from adenosquamous cell carcinoma are still not fully understood. Methods: We reviewed the hematoxylin-eosin stained slides and medical records of 31 cases of MEC of the lungs. The cases were classified as low and high grade according to the quantitative grading system formulated for MEC. High grade tumors were tested for an epidermal growth factor receptor (EGFR) mutation. Results: Twenty eight cases were classified as low grade and 3 cases as high grade. Histologically, lower glandular component, cellular atypia, necrosis, mitoses > 4/10 high power fields, and endolymphatic tumor emboli were typical characteristics of a high grade tumor. Although some tumors showed histologic features mimicking high grade tumors, they were classified as low grade tumors according to this quantitative grading system. Low grade tumors showed no recurrence or metastasis. However, among three patients with a high grade tumor, two had distant metastases and one died of disease. Additionally, an EGFR mutation was not detected. Conclusions: A high grade MEC was consistently different from a low grade tumor with regard to malignant histologic features and poor prognosis. Therefore, correct histologic grading is important in predicting the prognosis to avoid unnecessary treatment.