Rhabdomyosarcoma
Courtland Polley
Rhabdomyosarcomas (RMSs) are primary malignant soft tissue tumors that arise from embryonic mesenchyme with the potential to differentiate into skeletal muscle.1
They are rare overall but account for over half of all soft tissue sarcomas in children.
This is the third most common solid tumor in infants and children, behind neuroblastoma and Wilms tumor.1
250 to 300 new cases per year
75% of cases are diagnosed in children younger than 6 years
EPIDEMIOLOGY AND ETIOLOGY
RMSs can occur in any anatomical location in the body except for bone, even in places where there is no skeletal muscle (eg, the bladder, biliary tree) (Figure 58.1).
Most cases of RMS appear to be sporadic, but they have been associated with familial syndromes such as neurofibromatosis, Li-Fraumeni, Beckwith-Wiedemann, and Costello syndromes).2
CLINICAL PRESENTATION
The presenting signs and symptoms are variable and influenced by the site of origin, age of the patient, and presence or absence of distant metastases.
In general, the primary lesion has the appearance of a nontender mass, occasionally with overlying skin erythema3 (Figures 58.2 and 58.3).
DIAGNOSIS
Diagnosis is usually made by direct open biopsy.
There are no helpful markers or specific imaging studies.
Several grams of tissue are usually needed for the pathologist to identify histologic subgroups and subsequently provide adequate staging and to direct therapy.3
Trunk and extremity RMS should have excisional or incisional biopsy.
The incision should be placed so that it will not interfere with the incision needed for subsequent wide local excision.
The ultimate goal is wide local excision with clear margins.
Biopsies of genitourinary primaries are frequently performed endoscopically.
Regional lymph nodes are evaluated depending on location of the primary.
Sentinel lymph node mapping is advised for trunk and extremity lesions, as they have a high incidence of lymph node involvement.3
 Figure 58.1 Primary sites of rhabdomyosarcoma, osteosarcoma, and Ewing sarcoma, showing numbers of patients with primary tumors at specific sites. (Reprinted with permission from Abraham J, Gulley JL, Allegra CJ. Bethesda Handbook of Clinical Oncology. Philadelphia, PA: Wolters Kluwer Health; 2014.) |
 Figure 58.2 Rhabdomyosarcoma. An 8-year-old girl with a 3-week history of progressive swelling of the right eye. (Reprinted with permission from Penne R. Oculoplastics. Philadelphia, PA: Wolters Kluwer Health; 2019.) |
 Figure 58.3 Botryoid rhabdomyosarcoma on the vulva of a newborn girl. (Reprinted with permission from Requena L, Kutzner H. Cutaneous Soft Tissue Tumors. Philadelphia, PA: Wolters Kluwer Health; 2015.) |
Staging and Clinical Grouping
Pretreatment staging for RMS is performed to stratify the extent of the disease for different treatment regimens as well as to compare outcome (Table 58.1).
It is a variation on the TNM staging system, and it is based on primary tumor site, primary tumor size, clinical regional node status, and distant spread.3
The initial radiologic evaluation should include plain radiographs of the affected area, as well as CT scan or MRI of the primary site and surrounding structures.
MRI is increasingly considered the imaging method of choice for certain primary locations, such as the head and neck, extremity, parameningeal, and pelvic tumors.
Ultrasonography may provide additional information in patients with pelvic tumors (particularly the bladder) because the characteristic water density of urine helps in tumor localization.4
The clinical grouping system was developed by the Intergroup Rhabdomyosarcoma Group (IRS) and is based on the pretreatment and operative outcome (Table 58.2).
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