Perivascular epithelioid cell tumors (PEComas)

Perivascular epithelioid cells tumours (PEComas) are a group of related mesenchymal tumours and tumour-like conditions found in many locations. This group includes:

• angiomyolipoma (AML)
• clear cell 'sugar' tumour of the lung
• lymphangioleiomyomatosis (LAM)
• clear cell myomelanocytic tumour (CCMMT)
  • of the falciform ligament / ligamentum teres
• unusual clear tumours of other organs
  • pancreas
  • rectum
  • abdominal serosa
  • uterus - considered one of the commonest sites of involvement in the female pelvis
  • vulva
  • heart
  • orbit

Epidemiology

PEComas are far more common in females ⁴. 

Associations

• tuberous sclerosis complex

Pathology

Histology

All PEComas share similar and distinctive cellular morphology – peripheral epitheloid cells – which have no counterpart in normal tissue ⁴. These tumours appear as sheets and nests of epithelioid or spindle-shaped cells associated with blood vessel walls. They have granular eosinophilic cytoplasms. 

Immunohistochemistry

PEComas are characterised by immunoreactivity to smooth muscle and melanocytic markers ⁴.

• smooth muscle: actin, desmin
• melanocytic: HMB-45, melan-A

Radiographic features

Unfortunately, due to non-specific imaging appearances and the scarcity of reported cases no specific imaging features are recognised. These lesions seem to usually be solid but can be centrally necrotic ^5-7. They generally demonstrate prominent contrast enhancement ⁶. 

Treatment and prognosis

PEComas usually behave in a benign fashion although local recurrence and even malignant behaviour are encountered, mimicking malignant sarcomas. 

Surgical excision is usually curative.