What is Rb?

What is retinoblastoma?

Retinoblastoma (Rb) is a fast growing eye cancer of early childhood. This cancer develops in the cells of the retina, the light sensitive lining of the eye (see diagram). In the UK about 98% of children survive their retinoblastoma; this is true for both unilateral and bilateral disease. Nearly all of those with unilateral disease survive without further tumour. For those with bilateral disease there is, as explained in the section on 'second primary tumours', a risk that another type of tumour will develop in later life. Retinoblastoma has one of the best cure rates of all the cancers which develop in children.

Retinoblastoma occurs in two forms: a heritable form and a non-heritable form. Approximately 45% of children with retinoblastoma have the heritable form of the disease. When there is no previous family history of retinoblastoma, the disease is called sporadic. If a condition is heritable it can be passed on to future children. If someone has non-heritable Rb it usually means that they have Rb gene alterations only in retinal cells. More detail about the forms of Rb is in our genetics section.

In about two thirds of children, only one eye is affected, but in one third tumours develop in both eyes. When only one eye is affected, this is known as unilateral retinoblastoma, and when both eyes are affected it is called bilateral retinoblastoma. In some children who only have one eye affected at diagnosis, particularly those who are very young, it is possible for a tumour to develop in the second eye several weeks or even months after the diagnosis of retinoblastoma in the first eye.

The number of tumours found in the eye also varies: sometimes only one tumour develops however, there can be several tumours, and these may require more than one type of treatment.

How common is retinoblastoma?

Retinoblastoma is one of the less common cancers of childhood: in the United Kingdom it accounts for only about 3 out of every 100 cancers occurring in children under the age of 15 years. Between 40 and 50 children are newly diagnosed each year. It’s incidence is 1 in 20,000 births.

Retinoblastoma generally develops before 5 years of age and some children are born with the cancer.

What are the signs of retinoblastoma?

The signs of retinoblastoma include an abnormal appearance of the pupil, which tends to reflect light as a white reflex. This is usually only visible to the naked eye in low artificial lighting, or in photographs where a flash has been used. Sometimes children have a squint. Less common signs are deterioration of vision, a red and irritated eye without infection or a change to the colour of one iris.

For full details on the signs of retinoblastoma (Rb) visit our Signs and symptoms page.

What causes retinoblastoma?

In children with the heritable form of retinoblastoma, there is something wrong with a small piece of the genetic material on chromosome 13, called the RB1 gene. This affects all or many cells in the body. In some children with this form of retinoblastoma, the altered RB1 gene is inherited from a parent; in some cases, however, the alteration in this gene occurs during the early stages of fetal development, some time before the child is born. It is not known what causes the abnormality in the gene to develop. It is most likely to be a random mistake in the copying process which occurs when a cell divides. More details information can be found in our genetics pages.

Children with non-heritable retinoblastoma inherit normal copies of the RB1 gene from their parents. This form of retinoblastoma is also caused by a mistake in the RB1 gene, but this mistake occurs as a random event in one cell within the retina. This mistake then leads to a series of other genetic changes, which cause the retinoblastoma to form. Children with this form of the disease develop one tumour in one eye only and cannot pass on this alteration to their offspring.

For more detailed information on retinoblastoma and the genetics read our genetics pages.

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