Carcinoma ex pleomorphic adenoma

Carcinoma ex pleomorphic adenoma, abbreviated ca ex PA, is a rare malignant salivary gland tumour that arise from a pleomorphic adenoma.

Carcinoma ex pleomorphic adenoma
Diagnosis in short
LM DDx	salivary duct carcinoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, pleomorphic adenoma
Gross	firm
Site	salivary gland - usu. parotid gland
Signs	usu. parotid mass, firm
Prevalence	uncommon
Prognosis	dependent on stage, typically poor

General

Definition:

• Malignancy arising from a pleomorphic adenoma.

Diagnosis (either 1 or 2):

1. History of a pleomorphic adenoma at the same site.
2. Features of a pleomorphic adenoma and a carcinoma.

Epidemiology:

• Rare.
• Prognosis dependent on stage:
  • Good for early lesions - like PA.
  • Poor for advanced lesions.

Gross

• Usually mass lesion - partoid gland.

Microscopic

Features:

• Cells with cytologic features of malignancy - key feature.
• Architecture (any of the following):
  • Glands.
  • Nests.
  • Single cells (may be subtle).

Architectural patterns:

• Ductal carcinoma NOS (arising from ductal cells) - most common pattern for Ca ex PA.
• Myoepithelial carcinoma NOS (arising from myoepithelial cells).
• "Named carcinoma":
  • Salivary duct carcinoma - second most common pattern for Ca ex PA.
  • Mucoepidermoid carcinoma.
  • Adenoid cystic carcinoma.

Note:

• Often adenocarcinoma-like.
• Myoepithelial cells may be clear cells.

DDx:

• Salivary duct carcinoma.
• Mucoepidermoid carcinoma.
• Adenoid cystic carcinoma.
• Pleomorphic adenoma.

Subclassification

Extent of invasion:

1. Non-invasive AKA intracapsular AKA in situ.
2. Minimally invasive <=1.5 mm beyond the capsule.
3. Widely invasive >1.5 mm beyond the capsule.

Images

• Ca ex PA - showing ca and PA areas (nih.gov).
• Ca ex PA - showing capsule invasion (nih.gov).

IHC

Features - ca ex PA versus PA:

• Ki-67 elevated.
• HER2 +ve
• p53 +ve.

See also

• Salivary gland.
• Pleomorphic adenoma.
• Myoepithelioma.
• Salivary duct carcinoma.