Case 406 -- A female in her 30s with a right iliac fossa mass

Contributed by Ming Yin, MD, PhD and Uma Rao, MD
Published on line in November, 2004


The patient is a 35-year-old woman, who presented with a large right iliac mass and anemia. Physical examination showed no enlarged lymph nodes, and lungs are free of lesions on chest X-ray. The pelvic CT scan showed a destructive supra-acetabular mass involving the right iliac bone (Figure 1). An internal hemipelvectomy was performed following a biopsy of the lesion.


The specimen revealed a tumor predominantly located in the right iliac fossa, but on sectioning, it was found to extend into the bone and gluteal soft tissue laterally (Figure 2). The tumor was firm and white-tan, well-circumscribed, lobular and measured 10.0 x 8.0 x 6.5 cm. There were foci of central hemorrhage and possible necrosis (5-10% of section surface).


On routine hematoxylin and eosin stains, the neoplasm was mostly composed of small to intermediate sized spindle cells forming short intersecting fascicles (Figure 3). Some of the nuclei had a bullet shape, blunt at one end, pointed at the other. Vague nuclear palisades and storiform pattern could be seen at cellular areas. Compact and edematous areas were also observed. Some regions showed relatively low cellularity, while some regions demonstrate foci of epithelioid cells with moderate cytoplasm and vesicular nuclei, especially of the cells surrounding the vessels. Mitoses were abundant and averaged 20/10 HPF. Tumor necrosis was observed in approximately 10% surface area (Figure 4). The neoplasm infiltrated intertrabecular spaces of bone and adjacent skeletal muscle (Figure 4).


The tumor was diffusely positive for CD56 and CD99 and focally positive for S100, pancytokeratin, and bcl-2. Tumor cells were negative for CD34, desmin, SMMHC, HHF35, actin, c-kit (CD117), inhibin, estrogen receptors, and progesterone receptors (Figures 5, 6 and 7).


Conventional cytogenetic analysis showed mosaic female chromosome with a cell line representing a normal karyotype and an abnormal cell line with 60-71 chromosomes containing multiple numerical and structural abnormalities, including changes of chromosome 17 and 22. No abnormalities involving either chromosome X or chromosome 18 were detected. Fluorescence in situ hybridization analysis was unsuccessful probably due to the decalcification procedure performed on tissue block with pancytokeratin positive areas.


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