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

Abstract

The family of lesions thought to be composed at least in part of perivascular epithelioid cells, characterized as HMB-45-positive epithelioid cells with clear to eosinophilic granular cytoplasm and a propensity for a perivascular distribution, includes some forms of angiomyolipoma and lymphangioleiomyomatosis, as well as clear cell "sugar" tumor (CC-SUGAR). When composed predominantly or exclusively of epithelioid cells, it has been suggested that these lesions be classified as "perivascular epithelioid cell tumors" (PEComa). Four cases of uterine PEComa have been described in the literature, three of which exhibited aggressive behavior. We report the clinical, histologic, and immunohistochemical features of eight more examples of uterine PEComa. Patients ranged in age from 40 to 75 years (mean 54 years). Most patients presented because of abnormal uterine bleeding, and grossly a mass was present in the uterine corpus. Morphologically, the tumors could be divided into two groups (A and B). Group A tumors demonstrated a tongue-like growth pattern similar to that seen in low-grade endometrial stromal sarcoma and were composed of cells that tended to have abundant clear to eosinophilic pale granular cytoplasm, diffuse HMB-45 expression, and focal muscle marker expression. Group B tumors were composed of epithelioid cells with less prominent clear cell features, smaller numbers of which were HMB-45-positive. They also featured extensive muscle marker expression and a lesser degree of the endometrial stromal sarcoma growth pattern seen in group A tumors. Two of the four patients with group B tumors had pelvic lymph nodes involved by lymphangioleiomyomatosis, and one of these patients had the tuberous sclerosis complex. Seven of the eight patients with PEComas were treated by hysterectomy. All eight patients are alive and well, although follow-up of >2 years was available only for two patients. Uterine epithelioid smooth muscle tumors and low-grade endometrial stromal sarcomas were compared with the PEComas. Group A PEComas, group B PEComas, and epithelioid smooth muscle tumors were all parts of a continuous histologic spectrum, with group A PEComa at one end of the spectrum and epithelioid smooth muscle tumors at the other, while group B tumors shared features of both. PEComa was histologically and immunohistochemically distinct from endometrial stromal sarcoma. Our data and a review of the literature indicate that PEComa is a subset of HMB-45-positive epithelioid mesenchymal tumors of the uterus with an uncertain relationship to pure smooth muscle tumors. Although none of the patients in this study experienced recurrence during a short follow-up period, some reported in the literature have had recurrences; consequently, we think uterine PEComa should be considered a tumor of uncertain malignant potential until long-term outcome data for a larger number of patients become available.