Risks for retinoblastoma
Some things can affect your risk, or chance, of developing cancer. Certain behaviours, substances or conditions can increase or decrease the risk. Most cancers are the result of many risks. Childhood cancers are rare and there is less known about the risks. Most risks for childhood cancer are not modifiable. This means that you can’t change them.
A mutation, or change, in the retinoblastoma 1 (RB1) gene is the main risk for retinoblastoma.
Retinoblastoma accounts for about 2% of all cancers that occur in children, from birth to 14 years of age, and is the most common eye cancer in children. Most cases of retinoblastoma are diagnosed in children younger than 2 years old.
The following can increase the risk for retinoblastoma. None of these risks can be changed. Until we learn more about these risks, there are no specific ways to lower the risk for retinoblastoma.
RB1 gene mutation
Genetic mutations are changes to a
The eye starts to develop well before birth. Retinoblastoma is caused by a mutation to the RB1 gene in the immature cells of the retina (called retinoblasts). This mutation causes the retinoblasts to grow out of control.
There are 2 copies of the RB1 gene in every cell – one from each parent. There must be a change in both copies of the RB1 gene in a retinoblast for a retinoblastoma tumour to develop.
There are 2 different types of retinoblastoma. The type depends on where and when the RB1 mutation occurs and whether the mutation is inherited (passed to a child from a parent).
Non-heritable retinoblastoma (also called sporadic retinoblastoma) happens by chance. Children are born with 2 normal copies of the RB1 gene. A mutation of both copies of the RB1 gene in a retinoblast cell that occurs after birth causes a retinoblastoma tumour to form in the eye. Children with non-heritable retinoblastoma develop one tumour in one eye (called unilateral retinoblastoma). They will not pass the RB1 mutation on to their children. About half of retinoblastomas are non-heritable.
Heritable retinoblastoma is a result of a mutation in the RB1 gene that is either inherited, or the mutation happens in the egg or sperm before or soon after conception (called a germline mutation) or when the embryo is developing. In all cases of heritable retinoblastoma, a child is born with one copy of the RB1 mutation in all cells or in a portion of all cells of the body. This increases the risk of developing cancer in other parts of the body later in life. A mutation of the second copy of the RB1 gene then occurs in retinoblasts and causes retinoblastoma to form. In about 10% of children with heritable retinoblastoma, the mutation of the second copy of the RB1 gene was inherited from a parent. When this happens, it’s called familial retinoblastoma.
Children with heritable retinoblastoma can have more than one tumour and these tumours can develop in one or both eyes (called bilateral retinoblastoma). Children with heritable retinoblastoma can pass the RB1 mutation on to their children. About half of children with retinoblastoma have heritable retinoblastoma.
Children with heritable retinoblastoma have a higher risk of developing tumours in the pineal gland (called trilateral retinoblastoma). The pineal gland is located in the brain and controls the sleep cycle. Trilateral retinoblastoma usually occurs in children aged 20 to 36 months old.
Children with heritable retinoblastoma also have a higher risk of developing these other types of cancer later in life:
- bone cancer
- soft tissue sarcoma
- melanoma skin cancer
Amplification of the MYCN gene
A small number of children with retinoblastoma don't have an RB1 mutation. Instead, retinoblastoma is caused by an increased number of copies (called amplification) of the MYCN gene. The amplification of the MYCN gene causes retinoblastoma that grows quickly in one eye and usually occurs in children around the age of 4 months old.
Possible risks
The following have been linked with retinoblastoma, but more research is needed to know for sure that they are risks.
- being born to older parents
- being born to a parent who smoked while pregnant
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