Objective: To investigate the clinicopathological features and epidermal growth factor receptor (EGFR) gene mutation of primary pulmonary mucoepidermoid carcinoma (PMC).
Methods: Fifth-five cases of PMC were included in the study; their clinicopathological, immunohistochemical features were evaluated, and in 31 cases, paraffin embedded specimens were subjected to mutation analysis of exons 18, 19, 20 and 21 of the EGFR gene by ARMS method.
Results: There were 32 females and 23 males. The patients' age ranged from 11 to 68 years(mean 36 years). The tumor size ranged from 0.7 to 5.5 cm(mean 2.4 cm). The tumors were located in the segmental bronchus and upper segmental bronchus. The tumors were well-demarcated, had no obvious capsules, and protruded into the bronchial lumen. Microscopically, there were three types of tumor cells including squamous cells, mucin-producing cells and intermediate cells. Fifty-three cases were low grade, two were high grade and both showed lymph node metastases. Immunohistochemically the tumor cells were uniformly negative for TTF1, Napsin A and ALK (Ventana D5F3) in all 55 cases. The tumor cells were positive for CK7, and some squamous and intermediate cells were positive for p63 and CK5/6 in all 55 cases; whereas they were positive for p40 in 53 cases. The mucin-producing cells were negative for CK5/6, p63 and p40, but were positive for PAS in all 55 cases. The Ki-67 positive rate was <10% in the low grade PMC, and was about 80%-90% in the high grade cases. Follow-up information was available in 37 patients, with no recurrence or death. There were no EGFR gene mutations in all 31 patients of PMC.
Conclusions: PMC is a rare malignant salivary gland-type tumor occurring mainly in the central trachea of young patients.Most PMCs are low grade with good prognosis. The rate of lymph node metastasis of high grade PMC is high. Diagnosing PMC in small biopsies could be problematic. The lack of TTF1 expression is helpful to differentiate from other primary lung cancers. There is no EGFR gene mutation in PMC.