Definition
A malignant epithelial tumour composed of squamous cell, mucin-secreting cells and cells of intermediate type, identical to that occurring in the salivary glands.
Less than 1% of lung carcinomas are of mucoepidermoid type3. 50% of tumours occur in patients under 30 years of age3, including in children2. Most mucoepidermoid carcinomas are low grade.
Wheeze, asthma-like symptoms, haemoptysis and recurrent pneumonia result from bronchial obstruction.
Mucoepidermoid carcinomas form a well demarcated central mass. Punctate calcification may occur4.
The tumour is endobronchial and polypoidal. There is often cyst formation and a mucoid appearance. High grade lesions are more infiltrative.
Low grade mucoepidermoid carcinoma shows cystic and solid areas. Mucin-secreting columnar cells form glands, tubules and cysts, the mucus often resembling colloid, it may calcify. The glandular cells are bland with few mitoses. There are admixed non-keratinising squamous cells growing in sheets and showing intercellular bridges. Intermediate or transitional cells are oval with faintly eosinophilic cytoplasm. The stroma may hyalinise and may resemble amyloid. Mucus extravasation may result in a foreign body giant cell reaction, calcification or ossification.
In high grade mucoepidermoid carcinoma, the squamous and intermediate cells predominate. There is nuclear pleomorphism and hyperchromasia and frequent mitoses. High grade mucoepidermoid carcinoma overlaps adenosquamous carcinoma. Mucoepidermoid carcinoma is favoured by exophytic endobronchial growth, a lack of an in situ carcinomatous component and absence of individual cell keratinisation or squamous pearls, as well as by the presence of a low grade mucoepidermoid component.
Varying proportions of columnar, oncocytic and clear cells may be seen. Au unusual variant show a prominent lymphoplasmacytic component with Russell bodies and a giant cell reaction to inspissated mucus8. Similar tumour-associated lymphoid tissue has been described in salivary mucoepidermoid carcinomas.
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High grade: adenosquamous carcinoma
Low grade with florid lymphoplasmacytic stroma: lymphoma, inflammatory pseudotumour, lymph node metastasis. Normal nodal structures are absent.
Mucous gland adenoma: lacks intermediate and epidermoid cells but may also show prominent inflammation.
Resection. Low grade tumours may be removed by bronchoplastic sleeve resection3.
Low grade mucoepidermoid carcinoma spreads to local lymph nodes in less than 5% of cases. High grade tumours have a prognosis similar to that of non-small cell carcinomas and metastasis to regional lymph nodes, liver, bone, adrenal glands and brain1,3,7.
Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.
7 Yousem SA,Hochholzer L Mucoepidermoid tumors of the lung. Cancer 1987; 60:1346-52
This page last revised 29.3.2005.
©SMUHT/PW Bishop