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- A soft tissue cancer with features of skeletal muscle differentiation. Prognostic classification of rhabdomyosarcoma (RMS) currently depends on the following:
- Anatomic site of disease (stage)
- Extent of resection and spread (group)
- Underlying histology (alveolar vs. embryonal or other variants, e.g., botryoid)
- The most common pediatric soft tissue sarcomas (tumors of mesenchymal origin)
- Accounts for ∼5% of childhood cancer
- Boys at slightly increased risk compared to girls (incidence by gender of 1.5:1)
- Peaks in children <7 years of age, with another smaller peak in late adolescence
- Median age at diagnosis is 5 years.
- 4.5 cases per 1 million children per year
- U.S. annual incidence of about 350 cases per year
- Radiation exposure, including a possible connection to in utero exposure
- High birth weight associated with embryonal rhabdomyosarcoma in one study.
- About 90% of cases are sporadic.
- Several predisposing conditions:
- Li-Fraumeni (autosomal dominant)
- TP53 mutation leads to cancer predisposition through loss of DNA damage signaling.
- Increased risk for soft tissue sarcomas, osteosarcoma, adrenocortical carcinoma, choroid plexus carcinoma, leukemias, breast cancer, and other cancers
- Beckwith-Wiedemann syndrome (sporadic)
- Improper epigenetic regulation of 11p15 leads to an overgrowth syndrome.
- Increased risk of a range of embryonal cancers early in life, including Wilms tumor, hepatoblastoma, and RMS
- Neurofibromatosis type I and Costello syndrome (autosomal dominant)
- Mutational activation of HRAS (Costello) or loss of the RAS-negative regulator NF1 (neurofibromatosis) leads to unchecked RAS signaling and increased risk for RMS.
- No standard approach because most cases are sporadic
- Avoidance of radiation in patients with known predisposing syndromes (e.g., Li-Fraumeni syndrome)
- Alveolar rhabdomyosarcomas (ARMS; about 20% of cases) carry translocations t(2;13) or t(1;13) resulting in the fusion transcription factors PAX3-FOXO1 or PAX7-FOXO1.
- Alveolar histology and presence of PAX3-FOXO1 is a poor prognostic factor.
- Animal models combining expression of PAX3-FOXO1 and loss of either TP53 or CDKN2A recapitulate ARMS.
- Embryonal rhabdomyosarcomas (ERMS; about 60% of cases) commonly carry mutations in the RAS pathway as well as loss of heterozygosity at 11p15.
- Animal models of ERMS target activating Ras mutations to myogenic progenitor cells.
- The botryoid subtype of ERMS includes submucosal tumors with a favorable prognosis.
- The remainder of cases include pleomorphic or anaplastic histologies and also harbor a poor prognosis.
Commonly Associated Conditions
- Syndromes listed in “Genetics” have the highest association.
- CNS and genitourinary (GU) anomalies (Chiari malformations, horseshoe kidneys, etc.) in one autopsy-based report
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