Myoepithelioma/Mixed Tumor/Parachordoma



Myoepithelioma/Mixed Tumor/Parachordoma


Thomas Mentzel, MD









Grossly, this myoepithelioma arising in deep soft tissues represents a rather well-circumscribed, nodular neoplasm with gray-white cut surfaces.






Plasmacytoid myoepithelial tumor cells are arranged in clusters and solid areas and set in a myxohyaline stroma in this example of myoepithelioma of deep soft tissues.


TERMINOLOGY


Synonyms



  • Ectomesenchymal chondromyxoid tumor (of tongue)


Definitions



  • Neoplasms composed of epithelial &/or myoepithelial cellular elements in varying proportions



    • Tumor cells are set in hyalinized to chondromyxoid stroma and may show foci of ductal differentiation


  • Show overlap with mixed tumor of skin and soft tissues


  • Show overlap with myoepithelial carcinoma (malignant myoepithelioma) of skin and soft tissues


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Rare neoplasms


    • Increasingly reported


  • Age



    • Arise usually in adults


    • Significant number of cases arise in children < 10 years old


  • Gender



    • Slight male predominance


Site



  • Subcutaneous and deep soft tissue


  • Rare in skin


  • Very rare in bone


  • Upper > lower extremities > head/neck region > trunk


  • Less commonly on trunk and in head/neck region


Presentation



  • Painless mass


Treatment



  • Surgical approaches



    • Complete excision


Prognosis



  • Most neoplasms behave in benign fashion


  • Minority of cases may recur locally and metastasize



    • Benign-appearing neoplasms recur in < 20% of cases and do not metastasize


  • At present, no morphologic features reliably predict prognosis


  • Cytologic atypia represents most reliable prognostic parameter


  • Obvious malignant neoplasms behave aggressively



    • Metastases have been reported in up to 30% of cases


MACROSCOPIC FEATURES


General Features



  • Usually well-circumscribed neoplasms


MICROSCOPIC PATHOLOGY


Histologic Features



  • Nodular or lobular growth


  • Characterized by variable morphology


  • Varying proportions of epithelioid cells, spindled cells, plasmacytoid cells, clear cells


  • Cytoplasmic vacuolation is prominent in parachordoma-like cases


  • Neoplastic cells are arranged in nests, cords, solid formations


  • Ductal structures are not or only focally present


  • Tumor cells are embedded in hyalinized to chondromyxoid stroma


  • Divergent differentiation (squamous, adipocytic, cartilaginous, osseous) may be present


  • Nuclear pleomorphism is generally minimal


  • Few mitoses are usually present (< 2 mitoses per 10 high-power fields)




  • Dedifferentiation (progression) into frank myoepithelial carcinoma or sarcoma is seen rarely


  • May show loss of INI1 expression in considerable number of cases


  • Cutaneous myoepithelioma



    • Rare neoplasms


    • No ductal differentiation (vs. chondroid syringoma)


    • Form spectrum with chondroid syringoma and malignant myoepithelioma of skin


    • No connection with overlying epidermis


    • May infiltrate into subcutis


    • Broad variation in regard to growth patterns and cytomorphology


    • Local recurrences are rare


    • Lymph node metastases are very rare



      • Show increased atypia and proliferative activity


  • Malignant myoepithelioma (myoepithelial carcinoma)



    • Very rare neoplasms


    • Tend to be large


    • Severe cytologic atypia


    • Pleomorphic tumor cells


    • Increased proliferative activity


    • Tumor necrosis


    • Metastasize in up to 30% of cases (pulmonary and nodal metastases)


Cytologic Features

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Myoepithelioma/Mixed Tumor/Parachordoma
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