Retinoblastoma

Retinoblastoma is a disease in which malignant (cancer) cells form in the tissues of the retina. The retina is the nerve tissue that lines the inside of the back of the eye. The retina senses light and sends images to the brain by way of the optic nerve.

Although retinoblastoma may occur at any age, it usually occurs in children younger than 5 years of age. The tumor may be in one eye or in both eyes. Retinoblastoma rarely spreads from the eye to nearby tissue or other parts of the body. Retinoblastoma is usually found in only one eye and can usually be cured.

Symptoms and Diagnosis

These and other symptoms may be caused by retinoblastoma. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:

• Pupil of the eye appears white instead of red when light shines into it. This may be seen in flash photographs of the child.
• Eyes appear to be looking in different directions.
• Pain or redness in the eye.

The following tests and procedures may be used to diagnose retinoblastoma:

• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken. The doctor will ask if there is a family history of retinoblastoma.
• Eye exam with dilated pupil: An exam of the eye in which the pupil is dilated (opened wider) with medicated eyedrops to allow the doctor to look through the lens and pupil to the retina. The inside of the eye, including the retina and the optic nerve, is examined with a light. Depending on the age of the child, this exam may be done under anesthesia.
• Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.
• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the eye, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
• MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the eye. This procedure is also called nuclear magnetic resonance imaging (NMRI).

Retinoblastoma is usually diagnosed without a biopsy (removal of cells or tissues so they can be viewed under a microscope to check for signs of cancer).

Causes

All cancers are caused by dysfunctions of proteins involved in cell division, apoptosis, or DNA repair (see general characteristics). Dysfunctional proteins may arise from gene mutations or protein interactions with environments. 

Mutations in the RB1 gene are responsible for most cases of retinoblastoma. RB1 is a tumor suppressor gene, which means it normally keeps cells from growing and dividing too rapidly or in an uncontrolled way. Most mutations in the RB1 gene prevent it from making any functional protein, so it is unable to effectively regulate cell division. As a result, cells divide uncontrollably and form a tumor.

A small percentage of retinoblastoma cases are caused by a deletion in the region of chromosome 13 that contains the RB1 gene. Geneticists refer to this region as 13q14. Children with these chromosomal deletions may also have mental retardation, slow growth, and characteristic facial features (such as prominent eyebrows, a short nose with a broad nasal bridge, and ear abnormalities).

Stages

The following stages are used for retinoblastoma:

Intraocular retinoblastoma

Cancer is found in the eye but has not spread to tissues around the outside of the eye or to other parts of the body.

Extraocular retinoblastoma

The cancer has spread beyond the eye. It may be found in tissues around the eye or it may have spread to the central nervous system (brain and spinal cord) or to other parts of the body.

Treatment

Intraocular Retinoblastoma

If the cancer is in one eye and the tumor is large, treatment is usually enucleation (the removal of an organ or tumor in such a way that it comes out clean and whole, like a nut from its shell).

If the cancer is in one eye and it is expected that vision can be saved, treatment may include the following:

• Radiation therapy.
• Photocoagulation (a procedure that uses laser light to destroy blood vessels to the tumor, causing the tumor cells to die).
• Cryotherapy (any method that uses cold temperature to treat disease).
• Thermotherapy (the use of heat to destroy cancer cells).
• Chemotherapy (chemoreduction).

If the cancer is in both eyes, treatment may include the following:

• Enucleation of the eye with the most cancer, and radiation therapy to the other eye.
• Radiation therapy to both eyes or chemotherapy (chemoreduction) followed by local treatment. This may be done if there is a chance to save vision in both eyes.
• Surgery only, when vision cannot be saved.
• A clinical trial of subtenon chemotherapy combined with systemic chemotherapy and local treatment. Subtenon chemotherapy is the use of drugs injected through the membrane covering the muscles and nerves at the back of the eyeball.

Extraocular Retinoblastoma

There is no standard treatment for extraocular retinoblastoma. Radiation therapy and chemotherapy have been used. Treatment may be a clinical trial of high-dose chemotherapy with stem cell transplant.

Reference:

National Cancer Institute, USA.
Genetics Home Reference, U. S. National Library of Medicine