High grade sarcoma involving skeletal muscle with associated myofiber atrophy and reactive changes.
Rhabdomyosarcomas (RMSs) represent the most common soft tissue sarcomas of childhood. Histologically, they are classified as embryonal (including botryoid and spindle cell subtypes), alveolar, and pleomorphic. Diagnostic differentiation of these variants is important. The botryoid and spindle cell variants have a relatively good prognosis. Both alveolar and pleomorphic rhabdomyosarcomas are highly malignant tumors, and classical embryonal rhabdomyosarcoma (NOS) is considered to have an intermediate prognosis(1,2).
A specific translocation t(2;13)(q37;q14) or its variant t(1;13)(p36;q14) has been consistently identified in the alveolar subtype. The molecular lesions underlying these translocations have been fully elucidated with the discovery of fusion of the PAX3/FKHR genes in the t(2;13) and of the PAX7/FKHR genes in the t(1;13). In some alveolar RMSs,the fusion genes are amplified.(3,4).
To date, no characteristic chromosomal aberrations have been associated with the embryonal subtype of rhabdomyosarcoma. Hyperdiploid karyotypes with or without structural chromosome abnormalities have been observed frequently. However, structural abnormalities, when present, appear to be random. Extra copies of chromosomes 2, 8, 9, 11,12,13 and 20 have often been observed.(5). Comparative genomic hybridization as well as interphase fluorescence in situ hybridization studies are consistent with the cytogenetic findings(6). Karyotypic characterization of a human embryonal rhabdomyosarcoma cell line provided evidence stongly implicating alterations in chromosome 1 in the progression of rhabdomyosarcoma(7). Soft tissue tumors represent a heterogeneous group of mesenchymal lesions, and their classification is the subject of continuous debate(8). Chromosome analysis, molecular cytogenetics, and molecular assays may become increasingly useful in diagnosis, characterization and classification of soft tissue tumors. In the current case cytogenetic analysis provided evidence complementary to utrastructural findings supporting the myogenic identity of a high grade sarcoma not definitively characterized by light microscopic features or an extensive panel of immunohistochemical studies.
Contributed by Anna Mnuskin, MD, Urvashi Surti, Ph.D, Jean Dunn, M.D.