Epithelioid leiomyosarcoma in a non-immunocompromised infant: Additional differential diagnosis of pediatric "round cell tumors"

We report an 18-month-old Japanese girl with purely epithelioid leiomyosarc oma presenting as a huge intraabdominal mass. The patient had been well fro m birth and had shown no signs of immunodeficiency, She was negative for hu man immunodeficiency virus. Blood examination revealed elevated serum neuro n specific enolase (NSE), Histologically, the tumor was comprised of solid growths of round or polygonal cells with vesicular nuclei and often vacuola ted cytoplasm rich in glycogen, The tumor cells were positive for vimentin, NSE, and MIC2, and were negative for desmin and neurofilament. The age, cl inical presentation, and histologic findings mostly favored Ewing's sarcoma /primitive neuroectodermal tumor. Silver stain, however, demonstrated well- developed reticulin fibers often outlining individual tumor cells. An expan ded panel of immunostains showed that the tumor cells were intensely positi ve for smooth muscle actin, and ultrastructural study revealed abundant fin e cytoplasmic filaments with focal subsarcolemmal densities, various amount s of glycogen, and irregularly arranged, thick basal lamina The diagnosis o f epithelioid leiomyosarcoma was made. Following reduction in tumor size by chemotherapy, the serum NSE level was normalized, From the surgical findin g, the primary site was presumed to be the urachus or the urinary bladder d ome. Although extremely rare, epithelioid leiomyosarcoma should be added in the list of differential diagnoses of pediatric "round cell tumors."