Perivascular epithelioid cell neoplasms (PEComas): four malignant cases expanding the histopathological spectrum and a description of a unique finding

Abstract

Four cases of malignant PEComas were stained with smooth muscle actin, muscle specific actin, desmin, human melanoma black-45, melan-A, microphthalmia transcription factor, S100 and cyclin D1. One case was studied by electron microscopy (EM). Tumour locations were the thigh, elbow, retroperitoneum and bladder in association with a urachal cyst. There were two men and two women; the average age was 51.3 years, and the size ranged from 5.0-23.0 cm. In three cases, 50-95% of the tumour was composed of pleomorphic sarcomatous areas. All cases had at least focal clear-cell areas. One case showed a continuous single layer of perivascular clear cells remote from the tumour, transitioning to invasive nests and to PEComa. EM demonstrated these cells in apposition to and in direct contact with the abluminal surface of the basal lamina of the capillaries. We suggest the term "pecosis" for these areas. All cases were positive for two or more melanocytic markers and for at least one actin. S100 and desmin were focally positive in one case. Cyclin D1 was positive in 3:4 cases. Four cases of malignant PEComa are described with the existence of a unique lesion (pecosis) in one case. These tumours may manifest largely as sarcomas appearing to be undifferentiated and should be considered in their differential diagnosis.

Perivascular epithelioid cell tumor of the rib

“…While most reported PEComas have behaved in a benign fashion, malignant PEComa with the overexpression of cyclin D1 have been reported [25,26], suggesting that the cyclin D1 plays an important role in the genesis of malignant PEComa and serves as a marker of biological behaviors of PEComa. Recently, Folpe et al have proposed the provisional classification of PEComa to "benign", "uncertain malignant potential", and "malignant" [8].…”

Perivascular epithelioid cell neoplasms: pathology and pathogenesis

“…Equally important was the expansion of the morphologic spectrum of renal and hepatic AML to include "carcinoma-like" purely epithelioid variants [25,26], respectively, and the recognition of purely spindled PEComas, initially termed clear cell myomelanocytic tumors [3]. Most recently, PEComas showing a spectrum of histologic appearances and clinical behaviors have been described in a wide variety of intra-abdominal, visceral, gynecologic, soft tissue, bone, and cutaneous sites, including the falciform ligament/ligamentum teres, uterus, mesentery, heart, thigh and skull base, among others [3,5,7,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

A case of pararenal PEComa with extensive bone metaplasia

“…In sum, this unusual case belongs to the PEComa family, a recently defined group of tumours originated from perivascular epithelioid (PEC) cells [1,2] at multiple sites, encompassing angiomyolipoma, lymphangiomyomatosis, clear cell "sugar" tumour and rare tumours in other locations. They have a wide range of clinical, pathological and immunohistochemical features: clearly malignant [3,5], some of uncertain malignant potential and a few benign. This case would fulfil the criteria of the benign group: small (<5 cm), bland cellularity, no mitosisnecrosis-vascular invasion [1]; it had wide hyalinised areas and frequent calcification and osseous metaplasia, an unusual feature (which made it more evident in the CT scan).…”