Rhabdomyosarcoma
Basics
Basics
Basics
Description
Description
Description
- Rhabdomyosarcoma (RMS) is a malignant soft tissue tumor presumed to originate from a mesenchymal cell line shared with striated skeletal muscle.
- Occurs mainly as primary malignancy but can also be a component of heterogeneous neoplasms
- WHO classification of soft tissue tumors describes four main RMS subtypes:
- Embryonal RMS (ERMS): 60% of RMS cases
- Early onset and the most common subtype in children
- Commonly presents in the head, neck, and genitourinary areas
- Subdivided into:
- Classic
- Botryoid (6% overall embryonal): seen in infants, although can happen in <4-year-old patients
- Spindle cell: 3% of cases and affects young children
- Both botryoid and spindle cell variants have better prognosis than the classic variant
- Alveolar RMS (ARMS): 20% of pediatric cases
- Aggressive subtype
- More common in the trunk, perineum/perianal area, and extremities
- Spindle/Sclerosing: approximately 10% of cases
- Mostly found in the paratesticular region
- Anaplastic (children)/pleomorphic (adults): <10% of cases
- Typically seen in patients aged 30 to 50 years (rarely in pediatric population)
- Associated with Li-Fraumeni symptoms
- Demonstrates hyperchromatic enlarged nuclei
- Pathologic and molecular studies have now delineated up to five or six distinct subfamilies of RMS.
- Common primary sites:
- Head and neck (25%) presentation (common in young children, usually embryonal type)
- Genitourinary (31%, mostly embryonal type)
- Musculoskeletal (13%, most common in extremities primary sites in adolescents and adults, alveolar subtype)
Epidemiology
Epidemiology
Epidemiology
- RMS is the most common soft tissue sarcoma in pediatric population.
- Common metastatic sites: bone marrow, lung, lymph nodes
Incidence
- 4.5 cases of RMS per 1 million children per year
- Accounts for 50% of all soft tissue sarcomas in children and adolescents
- 50% of pediatric cases occur before the age of 10 years (often before age 6 years).
Prevalence
- Represents 3% of all pediatric tumors and 1% of all adult tumors
- Slight predilection for males (1.3:1 male-to-female ratio)
- More common in the African-American population
Etiology and Pathophysiology
Etiology and Pathophysiology
Etiology and Pathophysiology
- Originates from rhabdomyoblast cell
- Tumor is often >5 cm in size with poorly circumscribed border, white coloration, and infiltrative features.
Genetics
Genetic characteristics vary according to the RMS subtype:
- Alveolar:
- Linked to recurrent Forkhead box O1 (FOXO1) fusions (identified in 90% of cases)
- t(1;13)(p36;q14), causing formation of the fusion oncogenes PAX7-FOXO1
- t(2;13)(q35;q14), causing formation of the fusion oncogenes PAX3-FOXO1
- Embryonal:
- Multiple complex genetic aberrations, including MYOD1 mutations
- Loss or uniparental disomy of 11p15.5 +2, +8, +11, +12, +13, +20 affecting genes IGF-2, H19, CDKN1C, and/or HOTS
- Spindle cell/sclerosing:
- 8q13 rearrangements involving SRF-NCOA2 and TEAD1-NCOA2
Risk Factors
Risk Factors
Risk Factors
Largely unknown; however, appears to be increased risk of RMS in setting of:
- Rapid growth in utero
- Radiation exposure in utero
- Lower socioeconomic status
- Recreational drug use during pregnancy
Commonly Associated Conditions
Commonly Associated Conditions
Commonly Associated Conditions
- Beckwith-Wiedemann syndrome (11p15 mutations)
- Costello syndrome (germline HRAS mutations)
- Li-Fraumeni syndrome (germline TP53; known as p53 mutations)
- Neurofibromatosis type I (NF1 mutations)
- Noonan syndrome (PTPN11 mutations)
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