Retinoblastoma

10 February 2012

Retinoblastoma is a type of cancer that affects the lining of the eye (the retina). It is very rare, affecting around 40 children a year in Britain – about 3 per cent of all childhood cancer cases.

Retinoblastoma is an embryonal tumour and as such, most cases occur in very young children.

Retinoblastoma occurs in two forms, heritable and non-heritable, and it can be either unilateral (one eye) or bilateral (both eyes). All children with bilateral tumours have the heritable disease, whereas only 10 per cent of unilateral cases have the heritable form.

Incidence

Around 40 children are diagnosed with retinoblastoma every year in Britain. Almost all of those affected are under five, with more than 40 per cent of the incidence occurring within the first year of life.

Most of the bilateral cases – which represent just over a third of cases overall – are diagnosed in the first year of life.

Overall, incidence is similar among males and females but there is a male excess of bilateral retinoblastoma (5:4) and a female excess of unilateral retinoblastoma (6:5).

Causes

Retinoblastoma occurs as a result of two mutations in the retinoblastoma suppressor gene, RB1.

In the heritable (inherited) form of retinoblastoma, which accounts for about two in every five cases, the abnormal gene can be passed from a parent to their child, allowing the tumour to develop. People with the heritable form also have an increased risk of developing other types of cancer later in life.

Genetic counselling and support is available for families in which a member has retinoblastoma. Not all children of an affected parent will inherit the faulty gene but all children born into families with a history of retinoblastoma will be screened regularly during their first five years of life for signs of retinoblastoma so that treatment can be started early if a tumour does develop.

The causes of the non-heritable forms of retinoblastoma are not understood.

Survival

The survival rate for retinoblastoma is better than for any other cancer at 99 per cent.

Unfortunately, however, survival may be at the expense of some or all of the child’s sight.

Symptoms and diagnosis

Some children with retinoblastoma may have no symptoms but the disease will be detected by screening where there is a family history.

If there is no family history, the first sign of retinoblastoma is often a white pupil that does not reflect the light. This is called leucocoria and is sometimes detected in photographs taken using flash photograpy – the affected eye may look white in the photograph. Some children may have a squint or, if the tumour is large, a painful, red eye.

Diagnosis will be confirmed by an examination under anaesthetic. Unlike most other types of cancer, retinoblastomas can be diagnosed just by their appearance – a biopsy is not usually necessary.

Once retinoblastoma is diagnosed, other tests may be carried out to check the exact position and size of the tumour, and whether it has spread. This is known as staging. These tests may include an ultrasound scan, an MRI scan and a lumbar puncture. A bone marrow sample may be taken to check whether there has been any spread of the cancer to the bone marrow and a blood sample may be taken for genetic testing.

Intraocular retinoblastoma has not begun to spread to other parts of the eye or into the tissues surrounding the eye; extraocular retinoblastoma has spread beyond the eye and into the tissue surrounding it or to other parts of the body.

Treatment

Treatment depends on a number of factors including the number, position and size of the tumours in the eye. The primary aim of treatment is to get rid of the cancer. Some patients may lose some or all of their sight as a result although every effort is made to preserve sight.

Smaller tumours have treatment just to the eye itself with laser therapy, freezing therapy (cryotherapy) or heat therapy (thermotherapy) to destroy the tumour. Larger tumours may be treated with chemotherapy, radiotherapy or surgery to remove the eye (enucleation). A combination of treatments may be necessary.

Side effects of treatment

Any possible side effects will depend on the particular treatment being used. The child’s doctor will discuss the risks with you before treatment starts.

Read more: Side effects of treatment

References:
Cancer in Children: Clinical Management (5th edition). Eds: P A Voute, Ann Barrett, Michael C G Stevens and Hubert N Caron. Oxford University Press, 2005.
Childhood Cancer in Britain: incidence, survival, mortality. Ed by Charles Stiller. Oxford University Press, 2007.

Related Topics Retinoblastoma, types of childhood cancer