Perivascular epithelioid tumour of the uterus, PEComa

There is a family of tumours composed at least in part of HMB-45-positive/Melan-A-positive perivascular epithelioid cells. These include epithelioid angiomyolipoma, epithelioid lymphangioleiomyomatosis, clear cell "sugar" tumour, clear cell myomelanocytic tumour of ligamentum teres/falciform ligament and abdominopelvic sarcoma of perivascular epithelioid cells. There is an association of this family of tumours with the tuberous sclerosis complex. Where epithelioid perivascular cells predominate, the name perivascular epithelioid tumour or PEComa has been suggested.

Clinical features

Patients ranged from 40 to 75 years of age. Presentation was with uterine bleeding and a uterine mass1.

Histopathology

The tumour morphology varies:

• Group A: tongue-like growths, resembling those seen in low-grade endometrial stromal sarcoma. Cells have abundant clear to eosinophilic pale granular cytoplasm. HMB-45 positivity is strong and there is limited expression of muscle markers. One case showed conspicuous intranuclear pseudo-inclusions. Mitotic activity and necrosis were absent.

• Group B: Less resemblance to the growth pattern of endometrial stromal sarcoma, less prominent clear cell cytoplasm and lesser staining for HMB-45 but greater staining for muscle markers. There is an associating with tuberous sclerosis and lymphangioleiomyomatosis. This group appears to be intermediate in differentiation between group A and epithelioid smooth muscle tumours.

Immunohistochemistry

Uterine lipoleiomyomas are negative for HMB-45 (0/9)1.

Differential diagnosis

It is probably currently appropriate to stain all epithelioid mesenchymal tumours of the uterus for HMB-45

• Epithelioid or clear cell smooth muscle tumours. Uterine leiomyosarcomas sometimes have clear cell areas that locally express HMB-45: therefore doubt has been cast on the existence of uterine PEComa as an entity2. Epithelioid areas in leiomyosarcoma do not express HMB-452. Rarely, HMB-45 positivity has been reported in typical uterine leiomyomas and in normal myometrium.

• Low-grade endometrial stromal sarcoma

• Clear cell carcinoma

• Metastatic melanoma

• Placental site trophoblastic tumour

Prognosis

These are tumours of uncertain malignant potential, with some reports of aggressive behavior.

References

1 Vang, R., Kempson, R. L. Perivascular epithelioid cell tumor ('PEComa') of the uterus: a subset of HMB-45-positive epithelioid mesenchymal neoplasms with an uncertain relationship to pure smooth muscle tumors. Am J Surg Pathol 2002;26;1-13.

2 Hurrell DP,McCluggage WG. Uterine leiomyosarcoma with HMB45+ clear cell areas: report of two cases. Histopathology 2005; 47:540-2

This page last revised 7.5.2002.

©SMUHT/PW Bishop