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 RMS, although the diagnostic significance of each protein marker may vary depending on the type and location of the malignant cells. The alveolar type of RMS 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 RMS. 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 RMS, 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 RMS. 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 RMS 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.
Embryonal rhabdomyosarcoma is the most common type and comprises about 60% of cases.Outcomes vary considerably, with 5 years survival rates between 35% and 95% depending on the type of RMS involved, so clear diagnosis is critical for effective treatment and management. Accurate and quick diagnosis is often difficult due to the heterogeneity of RMS tumors and a lack of strong genetic markers of the disease, although recent research by UVA Health researchers discovered “multiple lines of evidence supporting [the gene] AVIL is powerful driver for both major types of rhabdomyosarcoma,” according to researcher Hui Li, PhD, of the University of Virginia School of Medicine’s Department of Pathology and UVA Cancer Center. (.) Malfunctions in AVIL, Li and his team found, play an essential role in the development of the two main subtypes of rhabdomyosarcoma. In a scientific paper outlining the findings, he and his colleagues describe rhabdomyosarcoma as “addicted” to the gene’s excess activity. They ultimately label AVIL a “bona fide oncogene” for rhabdomyosarcoma. Treatment usually involves a combination of surgery, chemotherapy, and radiation. Sixty percent to 70% of newly diagnosed patients with nonmetastatic disease can be cured using this combined approach to therapy. Despite aggressive multimodality treatment, less than 20% of patients with metastatic RMS are able to be cured of their disease. Types
Given the difficulty in diagnosing rhabdomyosarcoma, definitive classification of subtypes has proven difficult. As a result, classification systems vary by institute and organization. However, rhabdomyosarcoma in the 2020 WHO classification is listed as four histological subtypes: embryonal, alveolar, pleomorphic, and spindle cell/sclerosing.