Mucoepidermoid carcinoma (MEC) is the most common of the SGTTLs 9. The tumour is thought to account for ~ 0.2% of primary lung cancers 4. MEC may be encountered in any age group, however, most cases have been seen in adults 4. There appears to be slight male preponderance with a male-to-female distribution of almost 1.5:1 9.
Lesions typically occur in relation to the tracheobronchial tree (hence they are also termed muco-epidermoid carcinomas of the tracheobronchial tree). In larger series, no topographic predilection for any particular pulmonary lobe or segment has been discovered. Central location often leads to postobstructive mucoid and lipoid pneumonia 9.
Common presentation of this uncommon tumours may be as exophytic endobronchial tumour, potentially greater than 5 cm in greatest diameter. Usually well circumscribed and with smooth overlying mucosal surfaces, their cut sections are tan-gray or yellow.
May be solid, cystic or both, may show overtly mucoid features. Components comprise clear cells, squamoid cells or transitional polygonal cells, interspersed with areas containing mucus-secreting glandular cells.
They are divided into low- and high-grade lesions:
- low-grade tumours characteristically demonstrate bland cytologic features; mitotic activity is minimal or absent
- high-grade mucoepidermoid carcinoma demonstrates a greater degree of cytologic anaplasia in both its squamoid and glandular elements; areas of necrosis and haemorrhage may also be present
Differentials on biopsy
- low-grade MEC
- may resemble mucous gland adenoma (MGA), especially in small biopsies
- distinction between these two entities may be impossible without complete resection of the tumour
- high-grade MEC: distinction from NSCLC may be largely academic
- usually based on the absence of foci of conventional adenocarcinoma
- other usable features include absence of an in situ carcinomatous component and the presence of low-grade mucoepidermoid areas in some of these high-grade lesions
Symptoms are dependent on the size and location of the neoplasms. Large central tumours can cause symptoms of obstruction, with pneumonia, dyspnea or chest pain, whilst more peripheral lesions may be asymptomatic. In these cases, they are frequently encountered on routine chest X-ray.
CT features are can be variable and nonspecific, although a well-defined ovoid or lobulated intraluminal or lung peripheral mass with moderate to marked heterogeneous contrast enhancement may suggest towards the diagnosis 1.
Lesions may sometimes show punctate calcification and may adapt to branching feature of the airways 3.
May aid in differentiation from other lung tumours 5, but first of all, it has been shown to have high accuracy in detection of histopathological tumour differentiation 10-11:
- high-grade - high FDG-hypermetabolism (avid)
- low-grade - slight FDG-hypermetabolism (less or even non avid)
Hence prediction of prognosis (and need for more aggressive treatment) may be possible 10-11.
Treatment and prognosis
Most lesions are generally regarded as low grade 7,10 and overall prognosis may be more favourable than other forms of lung cancer.
For high-grade tumours prognosis may equate that of other forms of NSCLC s 9--11, hence adjuvant radiation and chemotherapy is often performed 9.
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- 2. Brassesco MS, Valera ET, Lira RC et-al. Mucoepidermoid carcinoma of the lung arising at the primary site of a bronchogenic cyst: clinical, cytogenetic, and molecular findings. Pediatr Blood Cancer. 2011;56 (2): 311-3. Pediatr Blood Cancer (full text) - doi:10.1002/pbc.22872 - Pubmed citation
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- 6. Kitada M, Matsuda Y, Sato K et-al. Mucoepidermoid carcinoma of the lung: a case report. J Cardiothorac Surg. 2011;6 (1): 132. doi:10.1186/1749-8090-6-132 - Free text at pubmed - Pubmed citation
- 7. Heitmiller RF, Mathisen DJ, Ferry JA et-al. Mucoepidermoid lung tumors. Ann. Thorac. Surg. 1989;47 (3): 394-9. Pubmed citation
- 8. Ishizumi T, Tateishi U, Watanabe S et-al. Mucoepidermoid carcinoma of the lung: high-resolution CT and histopathologic findings in five cases. Lung Cancer. 2008;60 (1): 125-31. doi:10.1016/j.lungcan.2007.08.022 - Pubmed citation
- 9. Leslie KO, Wick MR. Practical Pulmonary Pathology. Saunders. ISBN:1416057706. Read it at Google Books - Find it at Amazon
- 10. Jeong SY, Lee KS, Han J et-al. Integrated PET/CT of salivary gland type carcinoma of the lung in 12 patients. AJR Am J Roentgenol. 2007;189 (6): 1407-13. doi:10.2214/AJR.07.2652 - Pubmed citation
- 11. Park CM, Goo JM, Lee HJ et-al. Tumors in the tracheobronchial tree: CT and FDG PET features. Radiographics. 2009;29 (1): 55-71. doi:10.1148/rg.291085126 - Pubmed citation
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