This study describes the clinical, histologic, and immunohistochemical features of four cases of GI PEComa. The size of the tumors ranged from 3.5 to 6.0cm in diameter, and all were located in wall of the large bowel. Microscopically, the tumors were characterized by an epithelioid arrangement of tumor cells, which had abundant clear to pale eosinophilic granular cytoplasm, vesicular nuclei and prominent nucleoli. The stroma was rich in capillaries, a sinusoidal vasculature and thick-walled blood vessels. Mitotic figures were generally rare. Immunohistochemically, the tumors were positive for Vimentin (4/4), HMB-45 (4/4), Melan-A(4/4),alpha-smooth muscle actin (4/4), and desmin (3/4). The patients have been well with no evidence of disease at 8, 15, 32 and 36 months,respectively, after the surgical operation. GI tract PEComas should be regarded as tumors of an uncertain malignant potential until long-term outcome data for a larger number of patients become available.
"PEComas have been found in various organs and have a tendency to affect women with approximately 40% of tumors originated from the uterus , although some unusual sites can be also involved occasionally, such as vagina , orbit , small and large bowel , heart  prostate , bladder  and endometrium . Multifocal PEComas (PEComatosis) have been described in the literature . "
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Perivascular epithelioid cell tumor (PEComa) is a rare but distinct mesenchymal neoplasm composed of histologically and immunohistochemically unique perivascular epithelioid cells. Due to its relative rarity, little is known about the histogenesis and prognostic factors of this tumor. We describe a case of unusual mesenteric PEComa in a 38-year-old female patient with regional lymph node involvement. Histologically, the tumor was composed of sheet of epithelioid cells with abundant clear or eosinophillic cytoplasms. Extensive coagulative necrosis and a few mitotic figures (2/50 high power field) could be found in tumor. The epithelioid tumor cells were diffusely positive for HMB-45, Melan-A, and focally positive for calponin. One of enlarged mesenteric lymph nodes was observed to be involved by tumor. A diagnosis of malignant mesenteric PEComa with lymph node involvement was made. The patient received chemotherapy after total resection of tumor and segmental resection of involved jejunum. There was no sign of recurrence of tumor found in period of 6-month regular follow-up after chemotherapy. To our knowledge, this is the first case of malignant PEComa in mesentery accompanied with regional lymph node involvement. The literature on this rare tumor is reviewed and diagnostic criteria of malignant PEComa are discussed.
"Metastatic ASPS of the gastrointestinal tract may also be characterized by prominent nucleoli and clear cytoplasm may closely mimic PEComa, but ASPS is always negative for HMB-45 . Paraganglioma may rarely occur in the gastrointestinal tract, but the more organoid growth pattern, the positivity for synaptophysin, chromogranin A and the negativity for HMB-45 and SMA should lead to the correct diagnosis . "
[Show abstract][Hide abstract] ABSTRACT: Perivascular epithelioid cell tumors (PEComas) are a group of rare mesenchymal neoplasms. Gastrointestinal PEComas are exceptionally rare, there being only a few case reports in the literature involving the colon and small intestine. Nearly all PEComas show immunoreactivity for both melanocytic (HMB45 and/or Melan-A) and smooth muscle (actin and/or desmin) markers. A 36-year-old male was admitted to the hospital with acut- abdomen. At laparatomy, a nodular mass protruding from the ileum which clinically simulated a diverticulitis was noticed. Gross examination of the specimen revealed a 2 × 1,5 × 1 cm secondarily ulcerated, solid, nodular, gray white tumor mass in the ileal wall. Histologically, tumor cells were composed of nests of round-polygonal epithelioid cells with abundant clear to slightly eosinophilic granular cytoplasm and round vesicular nuclei. The nests were separated by thin fibrovascular septa. Minimal necrosis and low mitotic activity were noticed in the tumor. Immunohistochemically, tumor cells were positive for SMA, HMB45, and Melan-A and negative for CD10, RCC, CD45, CD117, CD34, EMA, and Desmin. Diagnosis was PEComa of the ileum. We report the case of ileal PEComa to remind the unusual presentation (diverticulitis) of these tumors, besides rarity and diagnostic difficulties.
[Show abstract][Hide abstract] ABSTRACT: Structure of liquids is discussed in terms of Voronoi figures and Delaunay polyhedra. Equations of the respective models and precise experimental data recently available for argon lead to calculated values of the coordination number z and the geometric parameter mu. The relation between z and mu is thus found empirically. Further, calculated values of coordination numbers are compared with those coming from thermal-neutron and X-ray scattering data. A selection among the existing methods of obtaining z from the radial distribution function g(R) is made. The method chosen enables one to find z[g(R)] corresponding to the Voronoi structure.
Physica A: Statistical Mechanics and its Applications 01/1975; 80(5):513-522. DOI:10.1016/0378-4371(75)90099-0 · 1.73 Impact Factor
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