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Dense Pattern of Embryonal Rhabdomyosarcoma, a Lesion Easily Confused With Alveolar Rhabdomyosarcoma

2013; Oxford University Press; Volume: 140; Issue: 1 Linguagem: Inglês

10.1309/ajcpa1wn7arpcmkq

1943-7722

Erin R. Rudzinski, Lisa A. Teot, James R. Anderson, Julie Moore, Julia A. Bridge, Frederic G. Barr, Julie M. Gastier‐Foster, Stephen X. Skapek, Douglas S. Hawkins, David M. Parham,

Bone Tumor Diagnosis and Treatments

Abstract Objectives: To examine whether the frequency of fusion-negative alveolar rhabdomyosarcoma (ARMSn) increased coincident with changes in the definition of alveolar histology. Methods: We re-reviewed alveolar rhabdomyosarcoma (ARMS) in the Children’s Oncology Group study D9803, comparing histopathology with fusion status. Results: Our review of 255 original ARMS cases (compared with a control group of 38 embryonal rhabdomyosarcomas [ERMS] cases) revealed that many had an ARMS-like densely cellular pattern with cytologic features and myogenin expression more typical of ERMS. Following re-review, 84 (33%) cases of original ARMS were rediagnosed as ERMS. All reclassified ERMS, including dense ERMS, were fusion negative, whereas 82% of confirmed ARMS cases were fusion positive. Total ARMS diagnoses returned to historic rates of 25% to 30% of all rhabdomyosarcomas, and ARMSn decreased from 37% to 18% of ARMS cases. The outcome of reclassified ERMS was similar to confirmed ERMS. Conclusions: To address the role of fusion status in risk stratification, pathologists should include both a histologic diagnosis and an evaluation of fusion status for all new ARMS diagnoses.