pulmonary mucoepidermoid carcinoma is a type of salivary gland tumor

  • disease: 1.pulmonary mucoepidermal carcinoma
  • patient/sx: 2.grow very large, can be endobronchial
  • mutation: 2.fusion transcript t(11;19)(q21;p13), between the mucoepidermoid carcinoma translocated 1 (MECT1) gene on chromosome 19p13 and mastermind-like 2 (MAML2) on chromosome 11q21
  • histology: 2.mucinous cells
  • treatment: 2.surgical resection

Pulmonary mucoepidermoid carcinomas, particularly when high grade, can be difficult to distinguish from adenosquamous cell carcinomas of the lung. Histologically, they can be distinguished by the presence of mucus secreting, squamous, and intermediate cells in a variety of architectural patterns (Figure 4). The mucus-secreting cells stain positive for periodic acid–Schiff and mucicarmine stains. The fusion transcript t(11;19)(q21;p13), between the mucoepidermoid carcinoma translocated 1 (MECT1) gene on chromosome 19p13 and mastermind-like 2 (MAML2) on chromosome 11q21 has recently been identified in most pulmonary mucoepidermoid carcinomas.

Pleomorphic adenomas are the most common type of salivary gland tumor in the head and neck but are very rare in the lungs. They can be central or peripheral and can grow to be very large. Mucus and mucous-secreting cells are not seen histologically.

Adenoid cystic carcinomas are the second-most common pulmonary salivary gland tumor. They most often arise in the large airways, are usually smaller than 4 cm, and are more common in men. They may be less distinct and more infiltrative, invading and growing along perineural spaces, the bronchial mucosa, and airway cartilage. They may be characterized by a t(6;9)(q22-23;p23-24) translocation leading to fusion between a v-myb avian MYB viral oncogene homolog and nuclear factor 1B.

Adenosquamous cell carcinomas can be difficult to distinguish from high-grade mucoepidermoid carcinomas. In addition to the presence of the above fusion transcript, tumor location (more peripheral for adenosquamous carcinomas) and the presence of a low-grade mucoepidermoid component within the tumor can help to distinguish the two.

Mucoepidermoid carcinoma is the most common type of pulmonary salivary gland tumor. It can be found from the trachea to the peripheral lung and can grow to be large. Most often, it is well defined and has an endobronchial component in the trachea or main bronchi. The median age of presentation is 45 years, and there is a slight male predominance. Cytologic features allow mucoepidermoid carcinomas to be divided into low (the majority) and high-grade variants. Lymph node involvement is uncommon. Treatment of mucoepidermoid carcinomas (and other pulmonary salivary gland tumors) is surgical resection when possible. Low-grade tumors have a very good prognosis, while the prognosis of those with high grade tumors can be poor.

  • The area in the red box shows mucinous cells (tumor cells with lots of mucin in their cytoplasm), and the area in the green box shows so-called "intermediate cells," which are nonmucinous tumor cells. The latter cells have morphologic features intermediate between truly squamous cells and glandular cells (hence the name). This mix is characteristic of mucoepidermoid carcinomas.

The patient described in this question had bland histologic feature, suggesting a low-grade tumor. A left lower lobe resection was performed, and he has remained disease free for 18 months. The low density areas within his tumor on CT imaging may have suggested the presence of mucus.1

Footnotes

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