Pleomorphic adenoma

Pleomorphic adenoma, abbreviated PA, is a very common benign salivary gland tumour.

Pleomorphic adenoma
Diagnosis in short
Pleomorphic adenoma. H&E stain. (WC/KGH)
Synonyms	benign mixed tumour
LM	proliferation of myoepithelium in a mesenchymal stroma +/- epithelium; cells in ducts = epithelial, cells not in ducts = myoepithelial, mesenchymal stroma = chondroid stroma (specific), others (require epithelium) mucochondroid, hyalinized, osseous, fatty, myxoid
LM DDx	myoepithelioma, carcinoma ex pleomorphic adenoma, epithelial-myoepithelial carcinoma, polymorphous low-grade adenocarcinoma, adenoid cystic carcinoma
IHC	S-100 +ve, SMA +ve, GFAP +ve
Site	salivary gland - usu. parotid gland, oral cavity, other sites
Signs	mass lesion
Prevalence	common
Prognosis	benign
Clin. DDx	other salivary gland tumours

It is also known as benign mixed tumour.

General

Features:

• Very common - approx. 60% of parotid gland tumours.
• May transform into a malignant tumour.
  • Other benign salivary gland tumours do not do this.
• Only benign childhood salivary gland tumour of significance.

Weinreb's dictums

1. Most common salivary tumour in all age groups.
2. Seen in all sites (unlike other benign tumours).
3. Recurrence and malignancy risk (unlike other benign salivary gland tumours).
4. Any part of a tumour that looks like PA makes it a PA.

Gross

• May have cartilaginous appearance.
• Typically well-circumscribed.

Image:

• PA in situ (iarc.fr).

Microscopic

Features:

• Proliferation of myoepithelium and epithelium (ductal cells) in mesenchymal stroma.
  • Cells in ducts = epithelial.
  • Cells not in ducts = myoepithelial.
• Mesenchymal stroma - important feature.
  • May be any of following: myxoid, mucochondroid, hyalinized, osseous, fatty.
    • Chondroid = specific for PA; can diagnose PA without an epithelial (ductal) component if chondroid is present.
    • Myxoid = not specific for PA.

Notes:

• Mesenchymal stroma not required for diagnosis -- if >5% ducts.
  • No chondroid stroma and <5% ductal cells = myoepithelioma.
• Look for, i.e. rule-out, poorly differentiated carcinoma: carcinoma ex pleomorphic adenoma.

Memory device: MEC = myoepithelium, epithelium, chondromyxoid stroma.

DDx:

• Myoepithelioma.
• Carcinoma ex pleomorphic adenoma.
• Epithelial-myoepithelial carcinoma.
• Polymorphous low-grade adenocarcinoma.
• Adenoid cystic carcinoma.
• Mucoepidermoid carcinoma - occasionally.

Images

Case 1

• 

  PA. (WC/KGH)

• 

  PA. (WC/KGH)

• 

  PA. (WC/KGH)

• 

  PA. (WC/KGH)

Case 2

• 

  PA - intermed. mag. (WC)

• 

  PA - intermed. mag. (WC)

• 

  PA - intermed. mag. (WC)

www

• PA - myxoid stroma (webpathology.com).

IHC

• S-100 +ve.
• SMA +ve.
• GFAP +ve.

Sign out

Left Partial Parotid, Partial Parotidectomy:
- Pleomorphic adenoma.
- Three benign lymph nodes.
- NEGATIVE for malignancy.

Block letters

PAROTID GLAND MASS, RIGHT, EXCISION:
- PLEOMORPHIC ADENOMA.
- FOUR BENIGN LYMPH NODES.
- NEGATIVE FOR MALIGNANCY.

Note:

• Complete excision is often elusive; stating "completely excised" on a surgical pathology report is unwise.

Micro

The sections show a lesion with spindled (myoepithelial) cells and an epithelial component, on a background of a chondromyxoid stroma. The lesion is encapsulated by a thin layer of fibrous tissue. No nuclear atypia is apparent. Mitotic activity is not identified.

Unremarkable parotid gland and lymph nodes are present.

Alternate

The sections show a lesion with spindled (myoepithelial) cells and an epithelial component, on a background of a myxoid stroma. The lesion is mostly encapsulated by a thin layer of fibrous tissue. A small focus of macrophages is present. Significant nuclear atypia is not identified. Mitotic activity is not apparent. Unremarkable parotid gland and a morphologically benign lymph node are present. Ink is seen on the tumour.

See also

• Salivary glands.