Contributed by Anna Mnuskin, MD, Urvashi Surti, Ph.D, Jean Dunn, M.D.
Published on line in January 2000
This previously healthy 21 year old male presented with a 6.5 cm mass in his right thigh. Surgical excision of the mass demonstrated an essentially circumscribed unencapsulated cystic tumor invading the right rectus femoris muscle. A portion of the tumor was sent for cytogenetic analysis.
Hypotetraploid male karyotype with many acquired numerical and structural abnormalities, resulting in significant chromosomal gains for chromosomes 2q,5,8p,9q and 11q. Chromosomal losses include 3q,4q,12q, 17,19 and 21.
Embryonal rhabdomyosarcoma has been karyotypically characterized by complex structural and numerical changes. Gain of an entire copy or parts of chromosome 2,8 and 11 are relatively common changes that have been implicated in a primary developmental role for these tumors. Our findings support the diagnosis of embryonal rhabdomyosarcoma.
Histologically, the tumor was composed of loosely textured, mitotically active, round to spindle shaped malignant cells, which defied immunohistochemical characterization. Extensive necrosis was also present.
Electron photomicrographs of the neoplasm showed several ultrastructural features consistent with myogenic origin, including the presence of cell processes with aggregated actin and myosin filaments, abundant mitochondria, and multiple gap junctions between cells.
Spindle cell tumor with numerous gap junctions and other features consistent with myogenic origin.