Salivary glands
Primary salivary gland neoplasms
Benign
Pleomorphic adenoma

Editor-in-Chief: Debra Zynger, M.D.
Bin Xu, M.D., Ph.D.

Topic Completed: 9 September 2019

Minor changes: 10 July 2020

Copyright: 2003-2020, PathologyOutlines.com, Inc.

PubMed search: Pleomorphic adenoma[TI] salivary glands[TI] full text[sb]

See also: Benign metastasizing mixed tumors

Bin Xu, M.D., Ph.D.
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Cite this page: Xu B. Pleomorphic adenoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/salivaryglandspleomorphicadenoma.html. Accessed August 7th, 2020.
Definition / general
  • Benign triphasic salivary gland neoplasm composed of epithelial (ductal) cells, myoepithelial cells and chondromyxoid stroma
Essential features
  • Triphasic salivary gland tumors with ductal cells, myoepithelial cells and stromal component
  • Most common salivary gland neoplasm
Terminology
  • Benign mixed tumor
ICD coding
Epidemiology
Sites
Etiology
  • Prior radiation increases the risk of developing pleomorphic adenoma
Clinical features
  • Slow growing, painless, well circumscribed mass involving salivary gland
Diagnosis
  • Diagnosis can be rendered on preoperative cytology or biopsy, showing typical metachromatic fibrillary stroma (in cytology) or triphasic growth pattern (in biopsy)
Radiology description
  • Mass with well defined or bosselated border, hyperintense on T2 MRI
Radiology images

Images hosted on other servers:

MRI T2 weighted:
hyperintense
well defined mass

MRI parotid tumor

Prognostic factors
  • Benign tumor: surgical resection with appropriate margin is considered curative
  • Enucleation is associated with 15 - 25% risk of local recurrence
  • Recurrences are usually within 18 months but can be up to 50 years later (Arch Pathol Lab Med 2008;132:1445)
  • Risk of malignant transformation is ~5%
  • Risk factors for malignant transformation: multiple recurrences, submandibular location, older age, larger size, prominent hyalinization, increased mitotic rate (if present, sample tumor more thoroughly), radiation exposure
Case reports
  • 6 year old girl with pleomorphic adenoma of the parotid gland (Children (Basel) 2018;5:E127)
  • 28 year old man with submandibular mass (Case #243)
  • 54 year old man with painless swelling over left half of upper lip for past 10 years (Case #392)
  • 84 year old man, a former smoker, with enlarging parotid gland lesion (Case #404)
  • Metastasizing pleomorphic adenoma with recurrent PLAG1 or HMGA2 fusion (Am J Surg Pathol 2019;43:1145)
Treatment
Clinical images

Images hosted on other servers:

Minor salivary gland tumor

Mass over mandible

Parotid tumor

Large submandibular mass

Parotid tumor

Gross description
  • Primary tumor: well demarcated, bosselated gray-white myxoid mass
  • Recurrent tumor: numerous myxoid to fibrotic nodules of various size, giving a shotgun bullet appearance
Gross images

Contributed by Bin Xu, M.D., Ph.D.

Primary pleomorphic adenoma

Recurrent pleomorphic adenoma


Case #392

External surface

Cut surface

Microscopic (histologic) description
  • Bosselated outer surface, often with tongue-like protrusions (pseudopods)
  • Typically has 3 components:
    • Epithelial (ductal) component forming the inner layer of cysts and tubules
    • Myoepithelial cells as the outer layer of cysts and tubules and scattered within the myxoid stroma
      • Cytology of myoepithelial cells can be plasmacytoid, spindle, epithelioid, clear or stellate
    • Stromal component is typically myxoid, chondroid or myxochondroid
      • It can also be hyalinized or fibrotic
  • Metaplastic changes may be seen, e.g. adipose metaplasia, osseous metaplasia, squamous metaplasia (sometimes with keratinization), sebaceous metaplasia and mucinous metaplasia
  • Intravascular permeation has been reported in a small percentage of cases and does not increase the risk of recurrence or distant metastasis
  • Other features that may be seen in pleomorphic adenoma include
    • Tyrosine crystal: dense amorphous eosinophilic floret shaped crystal
    • Increased cellularity: so called cellular pleomorphic adenoma
    • Increased mitotic activity
    • Myoepithelial rich area or tumor
Microscopic (histologic) images

Contributed by Bin Xu, M.D., Ph.D.

Encapsulated mass

Bosselated interface

Pseudopods

Recurrent pleomorphic adenoma

Triphasic tumor

Clear myoepithelial cells


Plasmacytoid myoepithelial cells

Spindle myoepithelial cells

Squamous and mucinous metaplasia

Adipose and osseous metaplasia

Tyrosine crystals


Contributed by Andrey
Bychkov, M.D., Ph.D.

Biphasic population


Case #404

Pleomorphic adenoma

Myoepithelial cells

Chondroid stroma

Myoepithelial cells

Cytology description
  • Matrix containing tumor
  • Typical feature is its unique fibrillary stroma
  • Mixture of myoepithelial cells, ductal cells and extracellular stroma
  • Myoepithelial cells are usually the predominant cell type with various cytomorphology, including round, polygonal, plasmacytoid, spindle, etc.
  • Ductal cells show bland cytologic features with organized honeycombing or ductal arrangement
  • Extracellular matrix shows characteristic feathery / fibrillary borders and bright magenta color on Romanowsky type stain and gray-green chondromyxoid features on Papanicolaou stain
Cytology images

Contributed by Bin Xu, M.D., Ph.D.

Diff-Quik smear

Papanicolaou stain



Contributed by Jen-Fan Hang, M.D.

Fibrillary extracellular matrix

Plasmacytoid
myoepithelial cells

Squamous metaplasia

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

Images hosted on other servers:

FISH for PLAG1

Sample pathology report
  • Parotid, left, parotidectomy:
    • Pleomorphic adenoma, 2.0 cm, margins negative for tumor
Differential diagnosis
Board review style question #1

A 2.5 cm parotid tumor is resected. The most common molecular alteration of this tumor is

  1. ETV6-NTRK3 fusion
  2. MYB-NFIB fusion
  3. PLAG1 fusion
  4. PRKD1 mutation
Board review answer #1
C. PLAG1 fusion (this is a pleomorphic adenoma)

Reference: Pleomorphic adenoma

Comment Here
Board review style question #2
Which of the following statements regarding pleomorphic adenoma is true?

  1. Carries nearly zero risk of recurrence or malignant transformation
  2. Characterized by architectural diversity and is composed of one single type of cells
  3. Is the most common salivary gland neoplasm
  4. Typically treated with enucleation
Board review answer #2
C. Pleomorphic adenoma is the most common salivary gland neoplasm

Reference: Pleomorphic adenoma

Comment Here
Board review style question #3

A 45 year old man presented with a 2.8 cm, slow growing mass at left parotid region. He underwent ultrasound guided FNA for evaluation. What is the best diagnosis?

  1. Basal cell adenoma
  2. Oncocytoma
  3. Pleomorphic adenoma
  4. Warthin tumor
Board review answer #3
C. Pleomorphic adenoma

Magenta colored extracellular matrix with feathery / fibrillary borders and intermingled bland myoepithelial cells are characteristic features for a pleomorphic adenoma.

Reference: Pleomorphic adenoma

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