Rhabdomyosarcomas are a malignancy of connective tissue in which abnormal cells are thought to arise from primitive muscle cells. They account for more than half of all tissue sarcomas (i.e. cancer of the connective tissue) in children. Other types of sarcomas are liposarcomas, fibrosarcomas and mesenchymomas. Rhabdomyosarcomas can occur anywhere in the body but occur more commonly near muscular structures, e.g. around the intestines, around the ocular muscles and in the cardiac muscle in tuberous sclerosis.¹ The most common locations of rhabdomyosarcomas are:

• Head and neck (35-40%).
• Bladder (20%).
• Muscles, limbs, chest and abdominal wall (15-20%).
• Other sites, e.g. testes.

Rhabdomyosarcomas are highly malignant and grow rapidly - but are now potentially curable.

Epidemiology

• Rhabdomyosarcomas account for 7-8% of all childhood malignant solid cancers with fewer than 60 children diagnosed per year (mostly under 10 years of age).² It is actually the most common soft tissue sarcoma in children.³ It has a slightly higher preponderance in males than in females.
• Rhabdomyosarcomas can occur at any age but approximately 87% of patients are younger than 15 years. Rhabdomyosarcoma rarely affects adults.³

Types

Rhabdomyosarcomas arise from rhabdomyoblasts - a primitive muscle cell. There are four types:

• Embryonal rhabdomyosarcoma - the cells have a similar appearance to embryo cells aged 6-8 weeks. This is the most common type and has a predilection for the head, neck and the genitourinary tract.
• Alveolar rhabdomyosarcoma - the cells have a similar appearance to embryo cells aged 10-12 weeks. This tends to affect older children and teenagers and has a more aggressive nature. It is associated with muscles of the trunk and limbs.
• Botryoid type - this is a variant of the embryonal type and presents as grape-like lesions in the vagina and bladder.
• Pleomorphic rhabdomyosarcoma - this entity is more common in adults and has a tendency to affect muscles of the extremities.

Aetiology

• Most cases are sporadic in nature.
• There is an increased risk in patients with certain genetic disorders, e.g. Li-Fraumeni syndrome, neurofibromatosis, fetal alcohol syndrome and nevoid basal cell carcinoma.
• Environmental factors that may increase the risk of rhabdomyosarcoma include parental use of marijuana and cocaine, intrauterine exposure to X-rays and previous exposure to alkylating agents.³

Presentation

Rhabdomyosarcomas usually present as an expanding lump or swelling, which may cause pain. Other features depend upon the area of the body affected. Examples include:

• Nose - nasal obstruction and discharge.
• Eyes - protrusion of the eyeball.
• Abdomen - pain and change in bowel habit.
• Bladder - haematuria.

Diagnosis

Non-resolving lumps in children should be investigated by a centre recognised by the United Kingdom Children's Cancer Study Group, as they will have better expertise in these rare tumours.

• Blood tests: FBC may show anaemia; LFTs may show a raised ALT and raised LDH. Urinalysis may show haematuria associated with renal tract involvement. Renal function tests and electrolytes should also be checked.
• Bone marrow studies may be required (to look for infiltration).
• Radiological imaging - this may include CXR, ultrasonography and may proceed to CT or MRI scanning. More recently, positron emission tomography (PET) using radioisotope fluorodeoxyglucose (18^F) (FDG-PET) scanning looks promising, especially in staging of the neoplasia.⁴
• Bone scan to look for metastases.
• Biopsy for diagnosis and molecular studies.
• MyoD1 is an immature protein found in developing skeletal muscle, which disappears once the muscle matures and can be used as an immunohistochemical marker.⁵

Staging

Initially, staging was identified by the Intergroup Rhabdomyosarcoma Study Group (IRSG) into the following groups:⁶

Management

• Surgery - this is recommended for all lesions, provided it is feasible, and as much of the tumour should be removed as possible. Surgery is only occasionally possible, as the tumour is usually deeply embedded in surrounding tissue. If the rhabdomyosarcoma is in an extremity then amputation is required. Surgery may also be the only way to obtain a tissue biopsy.⁷
• Chemotherapy - this is given postoperatively and preoperatively to shrink tumour size. Vincristine, dactinomycin (actinomycin D) and cyclophosphamide (VAC) have been considered the gold standard.⁸ Dose intensification has been used to try to improve outcomes in children with rhabdomyosarcomas. However, one trial looking at dose intensification of cyclophosphamide failed to find an improved outcome.⁸ There have also been good results with the use of etoposide and ifosfamide.⁷
• Radiotherapy - this is given postoperatively and occasionally preoperatively to shrink tumour size and commonly in head, neck and pelvic tumours.

Prognosis³

• The 5-year overall survival rate is 72% with two thirds of children being cured.²
• In patients with localised disease, overall 5-year survival rates have improved to more than 80% with the combined use of surgery, radiotherapy and chemotherapy.
• However, there has been little progress in managing metastatic disease with a 5-year event-free survival rate less than 30%.
• The embryonal type is the most treatable and has the most favourable prognosis.
• Location of the tumour also affects the prognosis, with orbital and genitourinary tract rhabdomyosarcomas having the most favourable prognosis.

Document references

1. Paulino AC, Okcu MF; Rhabdomyosarcoma. Curr Probl Cancer. 2008 Jan-Feb;32(1):7-34.
2. McDowell HP; Update on childhood rhabdomyosarcoma. Arch Dis Child. 2003 Apr;88(4):354-7. [abstract]
3. Cripe TP, Pediatric Rhabdomyosarcoma, Medscape, Jun 2011
4. Tateishi U, Hosono A, Makimoto A, et al; Comparative study of FDG PET/CT and conventional imaging in the staging of rhabdomyosarcoma. Ann Nucl Med. 2009 Feb;23(2):155-61. Epub 2009 Feb 19. [abstract]
5. Stuart A, Radhakrishnan J; Rhabdomyosarcoma. Indian J Pediatr. 2004 Apr;71(4):331-7. [abstract]
6. Childhood Rhabdomyosarcoma - Treatment Health Professional Version, National Cancer Institute, Aug 2011
7. Breitfeld PP, Meyer WH; Rhabdomyosarcoma: new windows of opportunity. Oncologist. 2005 Aug;10(7):518-27. [abstract]
8. Spunt SL, Smith LM, Ruymann FB, et al; Cyclophosphamide dose intensification during induction therapy for intermediate-risk pediatric rhabdomyosarcoma is feasible but does not improve outcome: a report from the soft tissue sarcoma committee of the children's oncology group. Clin Cancer Res. 2004 Sep 15;10(18 Pt 1):6072-9. [abstract]