Pediatric and Developmental Pathology 17, 406-408, 2014 DOI: 10.2350/14-06-1501-CR.1 © 2014 Society for Pediatric Pathology Pediatric Gastrointestinal PEComas: A Diagnostic Challenge M arco Pizzi , 1* I da di Lor enzo ,2 Emanuele S. d 'A mo r e ,3 Paolo D 'A ngelo ,4 and Rit a A laggio 1 department of Medicine-DIMED, General Pathology & Cytopathology Unit, University of Padova, Padova, Italy 2Pathology Unit, ARNAS Civico, Di Cristina and Benfratelli Hospital, Palermo, Italy 3Pathology Department, "San Bortolo” Hospital, Vicenza, Italy 4Pediatric Hematology and Oncology Unit, ARNAS Civico, Di Cristina and Benfratelli Hospital, Palermo, Italy Received June 1, 2014; accepted July 14, 2014; published online July 14, 2014. ABSTRACT Perivascular epithelioid cell tumors (PEComas) in the pediatric population are very rare and frequently arise in the gastrointestinal tract. These tumors are characterized by variable morphological and immunohistochemical features, which may pose significant problems in differential diagnosis with other gastrointestinal mesen chymal tumors in pediatric patients. In presenting an unusual pediatric case of gastrointestinal PEComa, we also discuss the possible differential diagnosis of this rare entity. Key words: clear cell sarcoma, gastrointestinal mesen chymal tumors, PEComa, pediatric pathology, SOX 10 INTRODUCTION Perivascular epithelioid cell tumors (PEComas) represent a broad family of mesenchymal neoplasms, characterized by peculiar morphological and immunohistochemical features. According to the current World Health Organi zation Classification of Tumors of Soft Tissues, the PEComa family encompasses several entities, including angiomyolipoma, pulmonary clear cell “ sugar” tumors, lymphangioleiomyomatosis, and unusual clear cell neo plasms of various anatomic origins [1], A recent survey by Doyle et al. indicated that gastrointestinal (GI) PEComas are characterized by unique morphological and immunohistochemical fea tures; this poses relevant problems in the differential diagnosis with other mesenchymal neoplasms of the GI tract [2], As such, GI PEComas can represent a diagnostic challenge, that only ancillary techniques (ie, immunohis- tochemistry and cytogenetics) can help to resolve. In the present case, we report the clinicopathological features of a pediatric case of primary intestinal PEComa and discuss the possible differential diagnosis of this extremely rare entity. * Corresponding author, e-mail: marcopizzi2002@yahoo.it CASE REPORT An 8-year-old Caucasian girl presented at Di Cristina and Benfratelli Hospital (Palermo, Italy) with mild abdominal tenderness and epigastric pain. Computed tomographic scan revealed an intraperitoneal mass (greater diameter 8 cm) that was partially adherent to the transverse colon. After surgical excision (complete resection with negative margins [RO]), gross examination revealed a roundish, pedunculated lesion with focal hemorrhagic areas. Histologic examination revealed that the tumor was composed of a fascicular proliferation of spindle to epithelioid cells, focally arranged in a storiform growth pattern. Intratumor blood vessels were tiny and incon spicuous, with fascicles of neoplastic cells often arranged around them. Despite the presence of occasional hemor rhagic areas, tumor coagulative necrosis was consistently absent. The neoplastic population was composed of medium-sized, spindle to polygonal elements, with amphophilic cytoplasm, elongated nuclei, finely dispersed chromatin, and an absence of evident nucleoli. The mitotic rate was extremely low (<2 mitoses/10 HPF) (Fig. 1A,B). At immunohistochemistry, neoplastic cells were positive for Melan-A, HMB-45, MiTF, c-Kit, and NSE, with consistent negativity for TFE3, desmin, smooth muscle actin (SMA), muscle-specific actin (MSA), SI00, and SOX 10 (Table 1 and Fig. 1C-F). Fluorescent in situ hybridization analysis did not demonstrate EWS gene translocations or other recurrent chromosomal aberrations. The overall clinical, morphological, immunohisto chemical, and cytogenetic data led to a final diagnosis of primary gastrointestinal PEComa. At present (8 months after clinical presentation) the patient is alive with no evidence of relapsing/recurring disease. DISCUSSION PEComas in the pediatric population are very rare and frequently arise in the GI tract (10 of 37 cases reported in the literature) [3-5]. Unlike their adult counterpart,