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Fibroma-like perivascular epithelioid cell (PEComa) tumor is an extremely rare family of mesenchymal tumors composed of cells co-expressing melanocytic and myogenic markers. To date, 13 cases of primary bone PEComa have been reported in the literature and five reported fibroma-like PEComas were found in the soft tissues of patients with tuberous sclerosis (TSC). However, no fibroma-like PEComa has been reported in bone, either sporadic or TSC-associated. Here we report the case of a 22-year-old man with known TSC, who presented for evaluation of an asymptomatic mass in his left fibula diaphysis that had been present for 5 years. He had no activity-related pain, numbness, weakness, or limitations in range of motion. Both 3-T MRI and CT demonstrated a tumor originating from the midshaft middiaphyseal fibula. Axial T1-weighted and fat-saturated T2-weighted fast spin echo images showed a well-defined lesion in the fibula with extension into the surrounding soft tissues. Whole body bone scan was negative for metastasis using technetium-99m. Renal ultrasound was unremarkable with no evidence of angiomyolipoma. Histopathology demonstrated isolated spindle cells in a dense collagenous matrix. By immunohistochemical staining, tumor cells were positive for HMB-45 and MiTF and partially positive for alpha-smooth muscle actin supporting a diagnosis of fibroma-like PEComa of the midshaft fibula. Although fibroma-like PEComa of bone is very rare, a bone tumor in the setting of TSC should raise suspicion for the diagnosis, in particular if histology demonstrates rare epithelioid cells in a densely fibrotic stroma.

Introduction: Perivascular epithelioid cell (PEC) is a cell type constantly present in a group of tumours including angiomyolipoma (AML), clear-cell «sugar» tumour (CCST) of the lung and extrapulmonary sites, lymphangioleiomyomatosis (LAM), and clear-cell tumours of other anatomical sites. It has morphologic distinctive features: epithelioid appearance with a clear to granular cytoplasm, a round to oval, centrally located nucleus and an inconspicuous nucleolus. Immunohistochemically, PEC expresses myogenic and melanocytic markers. Eleven cases of primary bone PEComa presentation have been described since 2002., Objective: To report a case of primary bone perivascular epithelioid cell tumour., Case Report: 24 year-old male presented with pain. X-ray revealed an osteolytic lesion at right proximal tibia with soft tissue extension. Evaluation of slides identified a bony perivascular epithelioid cell tumour without immunohistochemical study confirmation., Results: Patient was treated by surgical excision and adjuvant chemotherapy (epirubicin/cysplatin). After two years of follow-up the patient remains disease free., Conclusions: This is the first-case report in Latin America. Immunohistochemical stains were negative and we believe it may be due to non-described ethnic variations., (Copyright © 2018 SECOT. Publicado por Elsevier España, S.L.U. All rights reserved.)

Introduction: Perivascular epithelioid cell tumor (PEComa) is a family of rare mesenchymal tumors composed of histologically and immunohistochemically distinctive perivascular epithelioid cells (PECs). These tumors have been described at multiple anatomic sites. PEComas presenting in bone are especially rare and they have been reported to be either primary or metastatic lesions. None of them is located at the level of the foot., Patient: We report on a case of primary bone PEComa of the talus, the first one to be published to the best of our knowledge. Treatment and result: Limb sparing surgical treatment has been done using intralesional tumor removal, burring and application of argon beam at the tumor walls and primary filling of the tumor cavity by bone cement with so far absence of any tumor recurrence documented by multiple histological sections at second look operation nine months after primary surgery, where cement has been replaced by autologous bone graft, and by subsequent follow-up., Conclusions: PEComa is a very rare tumor, and its presence in bone is especially rare. The here reported case of PEComa presenting at the level of the talus is, to the best of our knowledge, the first case to be reported in the literature.

A 29-year-old male presented with a 6-month history of left hip pain. Radiography and CT demonstrated a 6-cm lytic lesion of the left acetabulum. F-18 FDG PET for staging of the biopsy-proven malignant PEComa demonstrated intense hypermetabolism corresponding to the lytic left acetabulum. The patient underwent left hemipelvectomy with reconstructive surgery. On a follow-up F-18 FDG PET scan 3 months after initial surgery, a left lung pleural-based 9-mm nodule with hypermetabolism (SUVmax 4.1) was discovered and pathologically proven to be metastases from the primary osseous PEComa.

PEComas other than angiomyolipoma, lymphangioleiomyomatosis, and clear cell sugar tumor of the lung are relatively rare, and PEComas presenting in bone are especially rare. To further characterize their clinicopathologic features, 6 cases of PEComa which first presented in bone were retrieved from the authors' consult and surgical pathology files, including both primary and metastatic lesions. Four patients were female and 2 patients were male. The age at diagnosis ranged from 35 to 71 years, with a mean of 51.5 years. As for the 3 cases known definitely to have arisen in bone, the primary sites were right tibia in 2 cases and thoracic vertebra in 1 case. In the 2 cases, presenting in scapula and femur respectively, the primary sites could not be determined with certainty. In 1 case, the lesion was first found in humerus, but the primary tumor proved to be located in the uterus. Histologically, all the tumors were composed of both epithelioid and spindle cells, showing a nested pattern with elaborate vasculature. The characteristic thin walled vessels around which tumor cells were arranged tightly, or in a radiating fashion were seen in all cases. Two or more worrisome features (tumor size >5 cm, infiltrative growth pattern, high nuclear grade, high cellularity, necrosis, and mitotic activity >1/50 HPF) were identified in 4 cases, of which 2 were primary bone tumors; these cases were classified as "malignant" histologically. We conclude that both the primary and metastatic PEComas can present in bone, although both are rare. Combining our findings with the few earlier published reports, it may be suggested that primary PEComa of bone tends to involve lower extremities (5/7 cases). Histologically, they show similar cytomorphology, nested architecture, and characteristic vessels as PEComas at other sites. In addition, a significant subset of the primary bone lesions seem to be malignant.