Rhabdomyosarcoma (muscle cancer)

• What is Rhabdomyosarcoma of Muscle
• Statistics on Rhabdomyosarcoma of Muscle
• Risk Factors for Rhabdomyosarcoma of Muscle
• Progression of Rhabdomyosarcoma of Muscle
• Symptoms of Rhabdomyosarcoma of Muscle
• Clinical Examination of Rhabdomyosarcoma of Muscle
• How is Rhabdomyosarcoma of Muscle Diagnosed?
• Prognosis of Rhabdomyosarcoma of Muscle
• How is Rhabdomyosarcoma of Muscle Treated?

What is Rhabdomyosarcoma of Muscle

Rhabdomyosarcoma of Muscle is a type of muscle cancer.

Muscle is the tissue responsible for movements of the body, and for changes in the shape and size of internal organs. It consists of parallel arrangements of highly specialised cells containing contractile elements – chiefly actin and myosin filaments.

There are 2 main types of muscle (based on their appearance under the light microscope): smooth muscle and striated muscle. Striated muscle can be further divided based on its location:

• Skeletal muscle has, as its name suggests, an intimate relationship with the bones of the skeleton and is responsible for movement of the bones of the body;
• Visceral striated muscle is histologically identical to skeletal muscle but occurs in association with the soft tissues – for example the tongue, pharynx and diaphragm; and
• Cardiac muscle is the striated muscle of the heart

Skeletal muscle is under voluntary control and is the major muscle component of the body. It is responsible for the maintenance of body posture and also for the gross and fine movements of the limbs. In addition, the skeletal muscle of the eye (the extraocular muscles) are responsible for eye movements; and the visceral striated muscle is responsible for important elements of speech, breathing and swallowing.

Statistics on Rhabdomyosarcoma of Muscle

It is uncommon, but is the primary soft tissue sarcoma of childhood and adolescence. It accounts for 5% of malignant solid organ tumours. More than 70% of malignant mesenchymal tumours are rhabdomyosarcomas and occurs with highest incidence in children and adolescents. The median age at presentation is 5 years with sex incidence being slightly male predominant.

Geographically, the tumour is found worldwide.

Risk Factors for Rhabdomyosarcoma of Muscle

The aetiology (cause) of rhabdomyosarcoma has not yet been established but several associations have been identified. These include: congenital malformations; rare congenital syndromes, such as Beckwith-Wiedemann syndrome and Recklinghausen syndrome; familial predisposition to tumour formation (autosomal dominant inheritance, chromosome 17); and maternal factors such as increased age at first pregnancy and maternal breast cancer.

Progression of Rhabdomyosarcoma of Muscle

This type of tumour spreads by contiguous extension into adjacent structures. Lymphatic spread can also occur, especially when the primary tumour arises in the genitourinary tract or in the limbs. Meningeal spread is common in tumours of the head and neck. Distant metastases through haematogenous spread occurs to sites such as lung, bone and bone marrow.

How is Rhabdomyosarcoma of Muscle Diagnosed?

General investigations may show anaemia or low platelet count if bone marrow is involved. Abnormal alkaline phosphatase levels may indicate bone involvement.

Prognosis of Rhabdomyosarcoma of Muscle

Before the advent of chemotherapy in the 1970s the outlook for patients with rhabdomyosarcoma was universally poor. A 5 year survival rate was less than 20%. More recently, however, the cure rate has risen to approximately 70% following the introduction of postoperative systemic chemotherapy.

Prognostic factors in rhabdomyosarcoma are the site and stage of the tumour, and the sex of the patient. Parameningeal head and neck tumours and intra-abdominal tumours have the worst prognosis, whilst those in the orbit and urogenital tract are associated with a good prognosis. Female patients have a worse prognosis than do males.

How is Rhabdomyosarcoma of Muscle Treated?

Treatment of rhabdomyosarcoma varies depending upon the site of the lesion, but revolves around surgical, chemotherapy and radiotherapy techniques. Surgery and radiotherapy are used to establish local control of the tumour. The early dissemination of this tumour has necessitated systemic chemotherapy to prevent the development of metastatic disease, and also to assist in the maintenance of local disease control. In low risk patients the most common regime used is vincristine and dactinomycin. Cyclophosphamide is often added to this regime. In patients with intermediate risk the standard regime is vincristine, dactinomycin and cyclophosphamide. This regime is also used in high risk patients with metastatic disease.

It is important to realise that the treatment of rhabdomyosarcoma is a very complicated process. Younger patients may suffer long-term sequelae of treatments to the disease. The surgical sequelae can be serious and immediately evident following wide excision of primary tumours. Consequences of the very high doses of radiotherapy required to establish control of the disease are less evident initially but develop following a lag period of some ten to fifteen years. These depend on the age of the patient and site of disease, but radiation of large fields, as is often required, can have serious adverse effects on internal organs. In addition, the development of post-radiation tumours such as osteosarcoma is a very real problem.

Improvement in symptoms is an important measurement. Specific monitoring may take place through careful clinical follow-up and serial imaging to detect disease recurrence or metastatic spread. Vigilance is also required in the early detection of new primary tumours (post-radiotherapy) in patients who have been cured of their rhabdomyosarcoma.

The symptoms that may require attention are somatic pain from bone metastases, visceral pain from lung metastases and neurogenic pain if nerve tissue is compressed.
Coughing and breathlessness from lung involvement may require specific treatment.

Additional symptoms due to specific sites involved – such as the orbit – may require specialist treatment approaches.

(Source: Dr David Dalley, St Vincent’s Hospital).