Salivary glands

Primary salivary gland neoplasms

Malignant

Myoepithelial carcinoma


Editorial Board Member: Lisa Rooper, M.D.
Deputy Editor-in-Chief: Kelly Magliocca, D.D.S., M.P.H.
Abeer Salama, M.D.
Bin Xu, M.D., Ph.D.

Topic Completed: 13 September 2021

Minor changes: 13 September 2021

Copyright: 2021, PathologyOutlines.com, Inc.

PubMed Search: Myoepithelial carcinoma salivary glands[TI] full text[sb]

Abeer Salama, M.D.
Bin Xu, M.D., Ph.D.
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Cite this page: Salama A, Xu B. Myoepithelial carcinoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/salivaryglandsmyoepithelialcarcinoma.html. Accessed October 18th, 2021.
Definition / general
  • Myoepithelial carcinoma of the salivary gland is a carcinoma that is composed exclusively or near exclusively of myoepithelial cells
  • May arise de novo or ex pleomorphic adenoma
Essential features
  • Carcinoma composed entirely of myoepithelial cells showing invasive growth
  • Subclassified as de novo or ex pleomorphic adenoma (ex PA)
  • Over 50% shows PLAG1 fusion
Terminology
  • Malignant myoepithelioma (not recommended)
ICD coding
  • ICD-O: 8430/3 - mucoepidermoid carcinoma
  • ICD-11: 2B67.Y - other specified malignant neoplasms of parotid gland
Epidemiology
Sites
Clinical features
Diagnosis
  • Definite diagnosis can only be rendered in resection specimen by demonstrating invasiveness and (near) pure myoepithelial population within the tumor
Radiology description
Radiology images

Images hosted on other servers:

Multinodular parotid mass (arrows)

Prognostic factors
Case reports
Treatment
  • Surgical resection with negative margin is considered the standard of care
Gross description
  • Gross appearance is nonspecific
  • Tumor is often present as an expansile, lobulated to multinodular, beige to white mass, sometimes with ill defined / infiltrative border
Gross images

Contributed by Abeer Salama, M.D. and Bin Xu, M.D., Ph.D.
Lobulated parotid mass

Lobulated parotid mass

Microscopic (histologic) description
  • Invasiveness is typically demonstrated as expansile invasive multinodular growth: myoepithelial carcinoma rarely shows infiltration of single cells / small clusters or desmoplastic reaction
  • Nodules often have a hypocellular center with hyalinized stroma or bland necrosis surrounded by a hypercellular peripheral zone
  • Tumor necrosis can be seen within the hypercellular central zone of a tumor nodule
  • Currently, there is no well defined, widely accepted grading system: presence of tumor necrosis is considered by some as a feature of high grade myoepithelial carcinoma (Am J Surg Pathol 2015;39:931)
  • Composed (near) entirely of myoepithelial cells showing various cytologic features, including clear cell, epithelioid, plasmacytoid or spindle cell morphology
  • Hyalinized, myxoid or myxochondroid stroma may be seen in myoepithelial carcinoma de novo and ex PA
  • Common architectural patterns include solid, trabeculae, cords, nests and single cells
  • Presence of pre-existing / residual pleomorphic adenoma component can be seen in myoepithelial carcinoma ex PA
Microscopic (histologic) images

Contributed by Abeer Salama, M.D. and Bin Xu, M.D., Ph.D.
Multinodular invasive growth

Multinodular invasive growth

Expansile lobulated growth

Expansile lobulated growth

Necrotic hypocellular central zone Necrotic hypocellular central zone

Necrotic hypocellular central zone

Myoepithelial carcinoma ex PA

Myoepithelial carcinoma ex PA

Epithelioid features

Epithelioid features


Plasmacytoid features

Plasmacytoid features

Clear cell features

Clear cell features

Spindle cell features

Spindle cell features

S100 immunostain

S100 immunostain

CAM5.2 immunostain

CAM5.2 immunostain

Calponin immunostain

Calponin immunostain

Cytology description
  • Hypercellular specimen composed entirely of myoepithelial cells
  • Myoepithelial cells shows a mixture of plasmacytoid, epithelioid or spindle morphology arranges as small groups or single cells (Cancer 2002;96:32, Kokyu To Junkan 1985;33:533)
  • Scant amount of metachromatic stroma, mitotic figures and nuclear pleomorphism may be present
Cytology images

Images hosted on other servers:
Diff-Quik stain

Diff-Quik stain

Positive stains
Negative stains
Molecular / cytogenetics description
Molecular / cytogenetics images

Images hosted on other servers:

Molecular signature (oncoprint)

Sample pathology report
  • Parotid gland, left; superficial parotidectomy:
    • Myoepithelial carcinoma, high grade, 3.5 cm (see comment and synoptic report)
    • Comment: The tumor shows a mitotic index of 8 per 10 high power fields. Tumor necrosis is noted. Immunohistochemistry studies show that the tumor is positive for S100, calponin and CAM5.2, whereas negative for HMB45. The morphologic and immunohistochemical features are most consistent with myoepithelial carcinoma.
Differential diagnosis
  • Myoepithelioma:
    • Benign counterpart of myoepithelial carcinoma
    • Encapsulated without evidence of invasion (being capsular, vascular and perineural)
  • Pleomorphic adenoma:
    • Similarity:
      • Pleomorphic adenoma can be myoepithelial rich and may contain areas with pure myoepithelial cells
      • Pleomorphic adenoma may have pseudopod(s) protruding outside of tumor capsule
    • Difference:
      • Pleomorphic adenoma lacks the multinodular / lobulated invasive growth of myoepithelial carcinoma and contains areas typical of pleomorphic adenoma with ductal, myoepithelial and stromal component
  • Polymorphous adenocarcinoma:
    • Both tumors contained one cell type and are positive for S100
    • Other myoepithelial markers, e.g. calponin and SMA, are typically negative or very focally positive in polymorphous adenocarcinoma
    • Polymorphous adenocarcinoma shows architectural diversity with single filing, trabecular, cribriform, papillary and solid growth pattern, whereas myoepithelial carcinoma usually has cord and solid architecture
    • Myxoid stromal component may be seen in polymorphous adenocarcinoma but is usually focal
    • Polymorphous adenocarcinoma shows mutations or fusion involving PRKD 1 / PRKD 2 / PRKD 3 genes, whereas myoepithelial carcinoma has frequent PLAG1 fusion
  • Myoepithelial tumor of the soft tissue:
    • Myoepithelial tumors arising from salivary glands or soft tissue are indistinguishable on histology and immunohistochemistry level (Head Neck Pathol 2020;14:121)
    • EWSR1 fusions with POU5F1, PBX1, ZNF444, KLF17 and PBX3 seem restricted to soft tissue myoepithelial tumors (Head Neck Pathol 2020;14:121)
    • Radiological correlation is essential to determine the site of origin
Board review style question #1
Myoepithelial carcinoma Myoepithelial carcinoma


A parotid tumor is resected from a 46 year old man. The tumor is positive for S100, cytokeratin AE1 / AE3 and calponin, whereas negative for AR. What is the diagnosis?

  1. Adenoid cystic carcinoma
  2. Myoepithelial carcinoma
  3. Pleomorphic adenoma
  4. Salivary duct carcinoma
Board review style answer #1
B. The low power H&E clearly shows invasion, which supports a diagnosis of carcinoma and excludes benign entities, such as pleomorphic adenoma. At high power, the tumor contains one type of tumor cells, which exclude all carcinoma with biphasic patterns (e.g. adenoid cystic carcinoma). The immunohistochemical profile is consistent with myoepithelial phenotype. Therefore, the correct diagnosis is myoepithelial carcinoma.

Comment Here

Reference: Myoepithelial carcinoma
Board review style question #2
Which of the following statement about the myoepithelial carcinoma of the salivary gland is true?

  1. It harbors PRKD1 fusion
  2. It has negligible risk of distant metastasis
  3. It is biphasic, composed of epithelial (ductal) and myoepithelial elements
  4. It may arise de novo or ex pleomorphic adenoma
Board review style answer #2
D. Myoepithelial carcinoma contains only one cell type (myoepithelial cells) and does not contain epithelial (ductal) cells. PRKD1 fusion is seen in polymorphous adenocarcinoma / cribriform adenocarcinoma. Myoepithelial carcinoma is relatively aggressive, with approximately 20% risk of distant metastasis. It may arise de novo or ex pleomorphic adenoma.

Comment Here

Reference: Myoepithelial carcinoma
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