The retina is the coating of the back of the eye made of specialized cells that process light and colour for us to see. Uncontrolled growth of retinal cells due to a change in a gene, known as the retinoblastoma (RB) gene, causes retinoblastoma (pronounced ret'-n-oh-bla-stoh'-muh).
Retinoblastoma is a rare form of cancer, affecting 1 in 15,000 to 1 in 30,000 live births. Retinoblastoma is considered a childhood cancer since 95% of cases occur in children less than 5 years of age.
There seems to be an equal chance of the condition occurring in either eye, in either boys or girls, and regardless of race. About 75% of cases occur in one eye, and about 25% of cases occur in both eyes.
The body's cells reproduce themselves throughout a lifetime – tissues wear out and cells are replaced in a controlled manner. Retinoblastoma, like all cancers, occurs when that control is lost and cells begin to divide at an unusually high rate. Researchers are still working on the exact reasons for the gene mutation in retinoblastoma. However, they have discovered familial and non-familial causes for the disease.
Retinoblastomas can be classified into 2 categories: one is caused by inheriting a defective gene (familial) and the other is caused by a random change in the RB gene during cell replication (sporadic). The main cause of retinoblastoma is through the sporadic form. About 90% of children with retinoblastoma have no previous family history of the disease. Meanwhile, children who have a parent with the disease only account for less than 10% of all diagnosed cases. Retinoblastoma that occurs in only one eye is usually not inherited. Retinoblastoma that occurs in both eyes is almost always inherited.
Although researchers are not completely sure of what causes the retinoblastoma gene to change and lead to retinoblastoma, they are aware of the risk factors for the condition.
Family history is the main risk factor for retinoblastoma. Children who inherit the altered gene have a 90% risk of developing retinoblastoma.
Smaller studies suggest that a parent infected with human papillomavirus (HPV) or a parent's type of job or work exposure may increase the risk of their offspring developing retinoblastoma, but these two observations are controversial within the medical community.
Symptoms and Complications
Over 80% of retinoblastomas are first detected by a family member or friend (compared to less than 20% by a doctor). Due to the age of the child, it is difficult for a parent to find out if a child has retinoblastoma since the child cannot communicate any problems with their eyes. However, it is important that a parent or caregiver look for any unusual signs that resemble retinoblastoma. Earlier detection typically leads to better outcomes.
Typical signs (more than 20% of cases) include:
- leukocoria (also known as a cat's eye reflex) – when light is shone into the eyes, a white reflection is seen, giving the impression that the pupil is white
- strabismus – when one eye does not seem to be looking at the intended target, either crossed inwards or deviated outwards
Because this condition affects the retina, the child's vision is highly at risk. Partial or total blindness to one or both eyes is a possible complication. When detected early, there is a very high survival rate, estimated at 90% to 95%. Although most children with retinoblastoma have one eye affected, it is possible for the cancer to spread to the other eye or to other parts of the body, in particular the brain, lungs, and bone. The metastasis, or spreading of the cancer, rarely occurs. If there is metastasis, the spread of the disease is usually seen 1 to 2 years after treatment of the original tumour.
Making the Diagnosis
Only a doctor can diagnose retinoblastoma based upon symptoms and diagnostic tests. If there is a strong suspicion of retinoblastoma based upon clinical signs (see Symptoms and Complications section), the doctor will use specialized equipment to look into the child's eyes. Additionally, the doctor may order imaging tests, such as a CT scan or MRI scan, to confirm the diagnosis. A biopsy (tissue sample) from the eye is not typically performed since this may unnecessarily damage the eye.
Treatment and Prevention
Several treatment options exist for retinoblastoma, however, treatment depends on the severity of the condition and whether or not the child has familial or non-familial retinoblastoma. If the doctor believes the patient can keep any part of their vision, laser therapy, or cryotherapy (freezing cancer cells) may be used.
Of the non-surgical options available, radiation therapy is one of the last resorts employed because of the potential side effects of damage to healthy tissue and the possibility of triggering a new non-ocular tumour (not in the eye) in the case of familial retinoblastoma. Chemotherapy is sometimes used to shrink the tumour before other treatment options are used.
Enucleation, also known as removal of the eye, is done only if a child's vision cannot be saved or if there is a high risk that the cancer will spread.
While there are no preventative measures for retinoblastoma, eye examinations should be considered. Children with a family history of retinoblastoma should be closely followed by an eye specialist until they reach 7 years of age. If only one eye is affected, periodic screening of the other eye should be conducted by an eye specialist until the age of 7 years. As well, siblings of a child with retinoblastoma should have their eyes routinely checked by an eye specialist.