Embryonal rhabdomyosarcoma (EMRS) is a rare histological form of cancer in the connective tissue wherein the mesenchymally-derived cells (rhabdomyoblasts) resemble the primitive developing skeletal muscle of the embryo.
[8] The Horn-Enterline classification uses morphologic characteristics to divide rhabdomyosarcoma into the embryonal, alveolar, botryoid, and pleomorphic subtypes.
[9] As a result, the World Health Organization currently takes into account both molecular genetics and morphology to classify rhabdomyosarcoma into the embryonal, alveolar, spindle cell/sclerosing, and pleomorphic subtypes.
[14][16] As the most common form of soft tissue sarcoma, RMS affects around 4.5 people per million individuals under the age of 20 in the United States.
[9] Embryonal rhabdomyosarcoma is commonly driven by a mutation in the RAS family of proto-oncogenes, creating a powerful signal which is now known to promote tumor growth by preventing muscle lineage progression by blocking expression of the transcription factor myogenin.
[19] Inhibition of this signaling pathway with a cancer medication, trametinib, has been recently shown to overcome this differentiation block and reduce tumor progression in animal models of embryonal rhabdomyosarcoma.
[4] Approximately 10% of ERMS cases include a loss of function mutation at TP53, which results in anaplasia, poor cellular differentiation that can be identified through nuclei that are larger and darker-colored than normal.
[17][9] Risk factors associated with embryonal rhabdomyosarcoma include cigarette smoking, older age of birth parent, x-ray exposure, and maternal drug use.
[9] Rhabdomyosarcoma is diagnosed through the presence of embryonic myogenesis, or skeletal muscle formation, which can be identified through morphological examination as well as assays containing myogenic markers.
[22] The performance of molecular genetic tests as well as matching the genotypic result to the clinical presentation are necessary to confirm the diagnosis of rhabdomyosarcoma as well as identify a subtype.
[9] Fusion-status is determined through the expression of certain proteins that indicate muscle differentiation, or immunomarkers, although the specific assay panel used for diagnosis depends on the tumor morphology.
[23][9] After a physical exam, formal diagnosis of RMS in adult patients requires a computed tomography (CT) scan, which can assess the areas affected and to delineate the tumor.
[22] In children, physicians may opt for magnetic resonance imaging (MRI) to limit radiation exposure in younger populations.
However, in "A Report From an International Consortium",[18] the authors analyzed patient data from the Children's Oncology Group (COG) and European paediatric Soft tissue sarcoma Study Group (EpSSG), hoping to identify and analyze any relationship between clinical outcomes and genetic mutations.
[18] Contrary to previous research, the findings of this study suggest that having RAS isoform mutations did not necessarily equate to a poor development of the disease.
[31] Additionally, imaging that shows a tumor greater than 5 cm, presence of metastases, or positive lymph node status can indicate poor prognosis.
[25] In contrast, infants less than 1 year old had the worst outcome, which may be associated with the lower doses of chemotherapy and radiotherapy administered and naive immune system.
[32] In order to create an optimal treatment plan for the individual, therapy is often based upon risk stratification (low, intermediate, or high risk) based on an individual's disease stage, size of tumor, progression of disease, surgery resection, age at diagnosis, and site of tumor.