Soft tissue
Uncertain differentiation
Myoepithelioma / myoepithelial carcinoma / mixed tumor


Topic Completed: 5 November 2020

Minor changes: 6 November 2020

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PubMed search: myoepithelioma [TIAB] NOT salivary gland & myoepithelial carcinoma [TIAB]

Borislav A. Alexiev, M.D.
William B. Laskin, M.D.
Page views in 2020: 6,467
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Cite this page: Alexiev BA, Laskin WB. Myoepithelioma / myoepithelial carcinoma / mixed tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuemyoepithelialca.html. Accessed January 23rd, 2021.
Definition / general
  • Myoepithelioma, myoepithelial carcinoma and mixed tumor of soft tissue are a group of uncommon neoplasms that share morphological, immunophenotypic and genetic features with their counterparts in salivary gland and skin
Essential features
  • Trabecular, reticular, nested or solid growth of variably spindled or epithelioid cells
  • Frequent myxoid or hyalinized stroma
  • Mixed tumors show ductal differentiation
  • Myoepithelial carcinoma shows moderate to severe nuclear atypia, increased mitotic activity and necrosis
  • Positivity for S100, EMA, keratin or GFAP
Terminology
  • Not recommended: parachordoma
ICD coding
  • ICD-O: 8982/0 - Myoepithelioma, NOS
  • ICD-O: 8982/3 - Myoepithelial carcinoma
  • ICD-O: 8940/0 - Mixed tumor, NOS
  • ICD-O: 8940/3 - Mixed tumor, malignant
  • ICD-11: 2F7C & XH3CQ8 - Neoplasms of uncertain behavior of connective or other soft tissue and myoepithelioma
Epidemiology
Sites
Pathophysiology
Etiology
  • Tumors appear to be sporadic and of unknown etiology
Clinical features
Diagnosis
Radiology description
Radiology images

Contributed by Borislav A. Alexiev, M.D.

MRI

Prognostic factors
Case reports
  • 4 year old girl and 6 year old girl with molecularly confirmed primary renal myoepithelial carcinoma (Am J Surg Pathol 2016;40:386)
  • 36 year old woman with a molecularly confirmed myoepithelioma of the metatarsal bone (Pathol Int 2019;69:42)
  • 40 year old man with a molecularly confirmed myoepithelial carcinoma with a rhabdoid morphology arising in the neck (Head Neck Pathol 2015;9:273)
  • 45 year old woman with a molecularly confirmed soft tissue myoepithelial carcinoma of the abdominal wall diagnosed on fine needle aspirate (Diagn Cytopathol 2015;43:421)
  • 54 year old man with molecularly confirmed myoepithelioma arising in the sacrum (Histopathology 2014;65:917)
Treatment
Gross description
Gross images

Contributed by Borislav A. Alexiev, M.D.

Soft tissue mass

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D. and William B. Laskin, M.D.

Soft tissue mass

Myxoid stroma

Vacuolated cytoplasm

Spindle cell morphology

Clear cytoplasm

Hyalinized stroma


Cytologic atypia

S100

AE1 / AE3

GFAP

Calponin

Cytology description
  • Moderately cellular smears showing loosely arranged clusters, sheets, isolated cells, rosette-like arrangement with fibrillary material within (Cytojournal 2017;14:14)
  • Round to oval, spindle, epithelioid and plasmacytoid cells in myxoid background (Diagn Cytopathol 2016;44:152)
  • Bland uniform, round to ovoid nuclei with finely distributed chromatin and eosinophilic or pale cytoplasm (Diagn Cytopathol 2016;44:152)
Positive stains
Negative stains
Electron microscopy description
Molecular / cytogenetics description
Molecular / cytogenetics images

Images hosted on other servers:

FISH

Sample pathology report
  • Left leg, biopsy:
    • Myoepithelioma (see comment)
    • Comment: The neoplasm is composed of epithelioid and spindle cells with eosinophilic cytoplasm arranged in anastomosing cords and nests. Nuclei are monomorphic, ovoid or round, with minimal atypia. Interspersed between the cells there is abundant myxohyaline stroma. Occasional mitotic figures are identified (2 mitoses/10 high power fields). The cells are positive for SMA, S100, keratin AE1 / AE3 and GFAP. The findings support the above diagnosis. Although the majority of morphologically benign myoepithelial neoplasms of soft tissue behave in a benign fashion, there is an approximate 20% risk for local recurrence.
Differential diagnosis
Board review style question #1
The most common gene rearranged in myoepithelial tumors is

  1. EWSR1
  2. FUS
  3. SS18
  4. ZNF444
Board review style answer #1
Board review style question #2

A 45 year old man presented with a left thigh mass. Hematoxylin-eosin stains demonstrated a nested and trabecular growth of small to medium sized spindled to epithelioid cells with uniform, round to ovoid nuclei and eosinophilic or pale cytoplasm in myxoid background. Occasional mitotic figures were identified (2 mitoses/10 high power fields). Immunohistochemical stains for S100, keratin AE1 / AE3, GFAP and calponin (focal) were positive in tumor cells while all of the following were negative: desmin, CD34, ERG and h-caldesmon. SMARCB1 / INI1 expression was preserved. Which of the following is most likely the correct diagnosis?

  1. Extraskeletal myxoid chondrosarcoma
  2. Ossifying fibromyxoid tumor
  3. Metastatic carcinoma
  4. Epithelioid sarcoma
  5. Myoepithelioma
Board review style answer #2
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