WCLC 2025 - Posters & ePosters-EP.06.03 Mucoepidermoid Carcinoma of the Lower Respiratory Tract With Few to None Intermediate/Squamoid Cells: A Challenging Tumor Series

EP.06.03 Mucoepidermoid Carcinoma of the Lower Respiratory Tract With Few to None Intermediate/Squamoid Cells: A Challenging Tumor Series

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This study examines five rare cases of mucoepidermoid carcinoma (MEC) of the lower respiratory tract characterized by a predominance or exclusivity of mucin-secreting cells, with minimal to absent intermediate-type or squamoid cells—cell types normally defining MEC. MEC is a malignant salivary gland-type tumor typically composed of mucin-secreting, squamoid, and intermediate cells, arising in central airways and presenting diagnostic challenges when squamoid or intermediate elements are scarce.<br /><br />The five cases (three females, two males, aged 15-69) involved tumors located endotracheally or endobronchially, mainly confined to tracheal or bronchial walls. Histologically, tumors exhibited glandular aggregates of mucin-secreting cells with cystic, mucin-distended spaces but lacked discernible intermediate or squamoid cells. Immunohistochemical staining showed diffuse cytokeratin positivity but minimal or absent staining for squamoid/intermediate markers (p40, CK5) and myoepithelial markers (calponin, S100). This atypical profile complicated diagnosis, broadening differential diagnoses to include mucous gland adenoma, hyalinizing clear cell carcinoma, and metastases from pulmonary or extrapulmonary mucinous or clear cell adenocarcinomas.<br /><br />To resolve diagnostic uncertainty, fluorescence in situ hybridization (FISH) for the MAML2 gene rearrangement—a genetic hallmark in MEC—was carried out in three cases, confirming the characteristic translocation and supporting MEC diagnosis. Clinical data excluded metastases from head and neck salivary gland tumors.<br /><br />This series highlights the diagnostic difficulty posed by MECs lacking typical squamoid/intermediate components. Immunohistochemistry may be insufficient or misleading, emphasizing the critical role of MAML2 FISH analysis to establish diagnosis. Recognizing this unusual MEC presentation is important despite it falling outside the classic histologic definition. The study represents the largest series describing MECs of the lower respiratory tract predominantly composed of mucin-secreting cells to date.

Asset Subtitle

Giuseppe Pelosi

Meta Tag

Speaker Giuseppe Pelosi

Topic Pathology and Biomarkers

Keywords

mucoepidermoid carcinoma

lower respiratory tract

mucin-secreting cells

squamoid cells

intermediate cells

MAML2 gene rearrangement

fluorescence in situ hybridization

immunohistochemistry

diagnostic challenges

tracheal tumors