Rhabdomyosarcoma – Cancer of Orbit

What is Rhabdomyosarcoma (RMS)?

Rhabdomyosarcoma (RMS) is the most common cancer originating from the soft tissue of the orbit in children. Orbit is the bony cavity in which the eye resides. It is common in pediatric age group and they are rare in adults.

Causes of RMS

Rhabdomyosarcoma is caused by some genetic predispositions. Changes in DNA can cause activation of genes promoting cell growth and suppression of genes which inhibit cell growth. This imbalance in the genetic influence on the cell growth and cell division leads to uninhibited growth of mesenchymal cells into this tumor.

The tumor originates spontaneously from cells which have the potential to differentiate into muscles. They don’t arise from the extra-ocular muscles themselves.

Histologic Types

There are 4 histopathologic variants of rhabdomyosarcoma:

  1. Embryonal: It is the most common histologic variety of rhabdomyosarcoma – more than 80% of all cases. They have good 5-year survival rate which is about 95%.
  2. Alveolar: About 9% of all rhabdomyosarcomas are of this variety. Although this is less common than embryonal type but is more malignant form. The 5-year survival rate for this type is about 65%.
  3. Pleomorphic: This is the least common type of rhabdomyosarcoma. The prognosis is good with a 5-year survival rate of 97%.
  4. Botryoid: This variety of rhabdomyosarcoma is rare. It does not arise primarily from the orbit. It originates in the conjunctiva or sinuses surrounding the orbit and secondarily invades the orbit.

Risk factors

Some medical conditions are known to be risk factors for rhabdomyosarcoma. Here are some of those conditions:

1. Li-Fraumeni syndrome

2. Neurofibromatosis

3. Beckwith-Wiedemann syndrome

4. Hereditary retinoblastoma

Symptoms and presentation

Rhabdomyosarcoma is a cancer found mostly in children. This tumor is quite rare itself but 90% of them are found in children under 16 years of age. The average age of onset of tumor is 5-7 years.

Proptosis (protrusion of the eyeball forwards) is usually the first symptom which is quite rapid in younger children. That is the reason why it is important to intervene as early as possible to save the life of the patient. In teenagers, the progression is slower.

There may be other associated symptoms as well, like swelling of the eyelids and redness of the eye. The upper eyelid may be drooped and the eye may be deviated form the normal direction.

Treatment of rhabdomyosarcoma

In all cases of progressive protrusion of eyeball, especially if it is rapid, an ophthalmologist must be consulted on an urgent basis. The doctor first examines the child to know the size and severity of the tumor and make a clinical diagnosis of rhabdomyosarcoma.

CT scan and MRI are then done to get more information about the size and extent of the tumor in the orbit. Invasion of adjacent areas by the tumor including the brain can be visualized on the scans. This information is vital to plan the treatment.

To detect distant metastases, the treating doctor may do chest radiography (x-ray), bone marrow aspiration and lumbar puncture to rule out involvement of other organs by metastasis.

Biopsy of rhabdomyosarcoma tumor helps in identifying histological subtypes. This makes planning of treatment and prediction of survival easier.

There are three main modalities of treatment for rhabdomyosarcoma as suggested by Intergroup Rhabdomyosarcoma Study Group (IRSG):

1. Radiation therapy: Radiotherapy is given over 6 weeks. The purpose of radiation is to kill the malignant cells and shrink the size of tumor.

2. Chemotherapy: The aim of chemotherapy is to kill tumor cells at microscopic level, not only in the orbit but also at distant sites where the tumor cells have metastasized.

3. Surgery: It is reserved for recurrent cases. Exenteration is the usual surgical choice in which all the contents of the orbit, including the eyeball, are removed in order to make sure that no tumor tissue is left in the orbit.

Rhabdomyosarcoma is a malignant disease. Early identification and diagnosis of this tumor can save the life of the patient. All cases of proptosis should be immediately examined by an eye specialist to rule out rhabdomyosarcoma and other tumors of the eye and surrounding tissues.

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