Case reports
Digestive PEComas: A solution when the diagnosis Fails to “fit”

https://doi.org/10.1053/j.anndiagpath.2004.08.008Get rights and content

Abstract

We report two cases of digestive/intra-abdominal PEComa. The first lesion developed in the caecum of a 36-year-old woman, the second in the pararectal region of a 35-year-old woman. The first tumor was formed from spindle cells arranged in fascicles, the second contained predominantly epithelioid cells with prominent nucleoli. Immunohistochemically, tumor cells expressed smooth muscle actin and melanocyte markers (HMB45), S-100 protein and CD117 were negative. Based on the morphologic aspect and, above all, on the immunohistochemical study the diagnosis of PEComa was retained for both lesions. In the gastrointestinal tract, the principal differential diagnoses of PEComas are gastrointestinal stromal tumors, particularly the round cell/epithelioid subtype, and metastases of carcinoma and melanoma. Other differential diagnoses include rhabdomyosarcoma, paraganglioma, leiomyosarcoma, and clear cell sarcoma.

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Materials and methods

Surgical resection specimens were fixed overnight in 10% neutral buffered formalin. Routine 4 μm-thick sections were prepared from paraffin-embedded tissue and stained with hematoxylin-eosin. Immunohistochemical stains were performed using the strepatavidin-biotin-peroxydase method and diaminobenzidine as chromogen. The antibodies included smooth muscle actin (SMA) (clone 1A4; Sigma-Aldrich, St Louis, MO; 1:20,000) desmin (clone P33; Dakopatts, Glostrup, Denmark; 1:160), HMB45 (clone HMB45;

Case 1

A 36-year-old woman underwent a colonoscopy for anemia and rectorrhagia which identified a pediculated and ulcerated caecal tumor measuring 3.5 cm. A hemicolectomy was performed and revealed a macroscopically circumscribed but nonencapsulated tumor. Histologically, the tumor was a vaguely fascicular proliferation composed of epithelioid and spindled “myoid” cells (the former in a clear majority) with a clear or eosinophilic granular cytoplasm (Fig 1). Certain nuclei contained large nucleoli

Case 2

A 35-year-old woman presented with a pararectal tumor, not associated with the ovaries or the uterus. The tumor was circumscribed but not encapsulated and attached by a thin pedicle to the rectal wall. It was formed almost exclusively of epithelioid cells with an eosinophilic finely granular cytoplasm and round vesicular nuclei containing a single, large central nucleolus (Fig 4). The cells formed cords, rows, and alveolar structures, and were separated by an abundant hyaline fibrous stroma

Discussion

Bonetti et al1, 2 were the first to recognize PEComas as a distinct entity and, in addition, coined the term PEComa. The use of this designation remains the subject of some controversy, specifically as to whether it should be used as a collective term for all perivascular cells tumors or if it this term should be reserved for the newer or more rare entities (such as uterine clear cell tumors and the myo-melanocytic tumor of the falciform ligament), epithelioid or not (as suggested by Bonnetti

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