Mucoepidermoid Carcinoma

 

 

Epidemiology / Etiology:

    • < 1% of lung carcinomas
    • 30-40 y. mean (wide range)
    • No association with smoking

 

Common sites:

    • 60-70% parotid
    • lesions in smaller salivary glands are more likely to be malignant
    • lung: central airways / endobronchial typically

 

Gross features:

    • circumscribed (not encapsulated) / well-defined
    • cut surface is pale, gray-white with small, mucin-containing cysts

 

Histologic features:

    • cords, sheets, or cystic configurations of squamous, mucous, and intermediate cells
    • intermediate cells are most abundant:
      • sheet-like arrangements
      • round to ovoid, and intermediate in size between ductal basal cells and polygonal epidermoid cells
      • epidermoid differentiation is often focal
      • eosinophilic or clear cytoplasm
      • even chromatin
    • glandular cells
      • eccentric nuclei
      • delicate cytoplasm
      • indistinct cell borders
    • squamoid cells
      • dense cytoplasm
      • distinct cell borders
    • subdivided into low, high grade
    • low-grade:
      • 3 cell types as above
      • Tumour islands contain both cystic and solid patterns
      • Cystic patterns often
        • Bland columnar cells with mucin and rare mitoses
      • Solid areas
        • Squamoid and/or intermediate cells, typically surroudnign cystic areas
      • Stromal calcification and ossification often with a granulomatous reaction around areas of mucous extravasation
      • Rare necrosis
    • High-grade (rare):
      • Atypical squamoid and intermediate cells mainly
      • Frequent mitoses
      • Frequent necrosis
      • Variable numbers of mucin-secreting cells
      • Carefully exclude adenosquamous carcinoma.  Following features favour high grade MEC:
        • Exophytic endobronchial growth
        • Surface epithelium lacking CIS
        • Absence of indivicual cell keratinization and squamous pearls
        • Transitional areas to low-grade MEC

 

Immunophenotype:

Marker:

Sensitivity:

Specificity:

 TTF-1 (neg)

 

Adenosquamous + in adenoCA areas 

Napsin (neg)

 

Adenosquamous +

 

Molecular features:

    •  MAML2 gene rearrangement (specific to MEC):
      • CRTC1-MAML2
      • both low-grade and high-grade MEC but more frequent in low-grade
    • EGFR mutation (some reported)
      • Unknown significance

 

Other features:

    • PET positive usually
    • May involve lymph nodes
      • More common in high-grade
    • Prognosis:
      • Low-grade: good prognosis
      • High-grade: similar behavior to other NSCLC
      • Positive resection margin is poor prognostic factor
      • Positive lymph node mets is poor prognostic factor

 

References:

    •  Travis WD et al. (eds.)  WHO Classification of Tumours of the Lung, Pleura, Thymus and Heart (2015)