<unk>  is often difficult to diagnose due to its similarities to other cancers and varying levels of differentiation. It is loosely classified as one of the small-blue-round-cell tumors due to its appearance on an H&E stain. Other cancers that share this classification include neuroblastoma, Ewing sarcoma, and lymphoma, and a diagnosis of<unk>  requires confident elimination of these morphologically similar diseases. The defining diagnostic trait for<unk>  is confirmation of malignant skeletal muscle differentiation with myogenesis (presenting as a plump, pink cytoplasm) under light microscopy. Cross striations may or may not be present. Accurate diagnosis is usually accomplished through immunohistochemical staining for muscle-specific proteins such as myogenin, muscle-specific actin, desmin, D-myosin, and myoD1. Myogenin, in particular, has been shown to be highly specific to<unk> , although the diagnostic significance of each protein marker may vary depending on the type and location of the malignant cells. The alveolar type of<unk>  tends to have stronger muscle-specific protein staining. Electron microscopy may also aid in diagnosis, with the presence of actin and myosin or Z bands pointing to a positive diagnosis of<unk> . Classification into types and subtypes is accomplished through further analysis of cellular morphology (alveolar spacings, presence of cambium layer, aneuploidy, etc.) as well as genetic sequencing of tumor cells. Some genetic markers, such as the PAX3-FKHR fusion gene expression in alveolar<unk> , can aid in diagnosis. Open biopsy is usually required to obtain sufficient tissue for accurate diagnosis. All findings must be considered in context, as no one trait is a definitive indicator for<unk> . Staging Following diagnosis and histopathological analysis, various imaging techniques may be used, including MRI, ultrasound, and a bone scan in order to determine the extent of local invasion and any metastasis. Further investigational techniques may be necessary depending on tumor sites. A parameningeal presentation of<unk>  will often require a lumbar puncture to rule out metastasis to the meninges. A paratesticular presentation will often require an abdominal CT to rule out local lymph node involvement, and so on. Outcomes are strongly tied to the extent of the disease, and its early mapping is important for treatment planning. The current staging system for<unk>  is unusual relative to most cancers. It utilizes a modified TNM (tumor-nodes-metastasis) system originally developed by the IRSG. This system accounts for tumor size (> or <5 cm), lymph node involvement, tumor site, and presence of metastasis. It grades on a scale of 1 to 4 based on these criteria. In addition, patients are sorted by clinical group (from the clinical groups from the IRSG studies) based on the success of their first surgical resection. The current Children's Oncology Group protocols for the treatment of<unk>  categorize patients into one of four risk categories based on tumor grade and clinical group, and these risk categories have been shown to be highly predictive of outcome. Tumor site Risk classification Head and neck (orbit), biliary tract, genitourinary (excluding bladder and prostate) Favorable Cranial parameningial, bladder, extremities, prostate, other Unfavorable
Rhabdomyosarcoma
Myosarcoma
Pyomyoma
Rhabdomyoma
Hemangiosarcoma
Liposarcoma
Angiosarcoma
Fibrosarcoma