Conditions & Treatments

Heritable Retinoblastoma - What it is

What is retinoblastoma?

Retinoblastoma is a rare form of eye cancer typically diagnosed in children before 7 years of age. It develops in the retina, a vital part of the eye that enables us to see colour and light.

It can occur in one (unilateral) or both (bilateral) eyes, though only one eye is affected in around two-thirds (60%) of all cases.

The diagnosis of retinoblastoma in young babies and toddlers may be made during routine eye examinations, following which the child should be referred to an eye specialist (ophthalmologist).

How common is retinoblastoma?

Retinoblastoma is not common. It makes up 2-3% of cancers diagnosed in children. It affects about one in 15,000 to 18,000 children.

What is heritable retinoblastoma?

There are two types of retinoblastoma

Heritable
Caused by a faulty RB1 gene that was inherited, or could have developed at birth. It is found in every cell of the body.
Non-inheritable
Caused by chance events and/or environmental factors that resulted in a faulty RB1 gene that is only found in the tumour cells of the eye.

It is important to identify and differentiate between non-inheritable and heritable retinoblastoma as the heritable form carries other health risks that are not found with the non-inheritable form. Family members may also be at risk if the heritable form is identified.

Differences between heritable and non-inheritable retinoblastoma

Heritable retinoblastoma	Non-inheritable retinoblastoma
Faulty RB1 gene present in all cells in the body Usually affects both eyes (bilateral), though about 10% may only have one eye affected Usually diagnosed at 1 year of age Can be passed down in families	Faulty RB1 gene present only in tumour cells Affects only one eye (unilateral) Usually diagnosed at 2 years of age Not passed down in families
Children with heritable retinoblastoma are at an increased risk of: Developing new retinoblastoma tumours Developing other cancers Passing down the condition to their future children Their other family members may also be at risk.	Children with non-inheritable retinoblastoma are usually not at risk of passing down the disease to their children, and their family members are not at risk. They also have a much lower risk of developing a second retinoblastoma tumour or other cancers, compared to those with heritable retinoblastoma.

Heritable retinoblastoma

Non-inheritable retinoblastoma

Faulty RB1 gene present in all cells in the body
Usually affects both eyes (bilateral), though about 10% may only have one eye affected
Usually diagnosed at 1 year of age
Can be passed down in families

Faulty RB1 gene present only in tumour cells
Affects only one eye (unilateral)
Usually diagnosed at 2 years of age
Not passed down in families

Children with heritable retinoblastoma are at an increased risk of:

Developing new retinoblastoma tumours
Developing other cancers
Passing down the condition to their future children

Their other family members may also be at risk.

Children with non-inheritable retinoblastoma are usually not at risk of passing down the disease to their children, and their family members are not at risk.

They also have a much lower risk of developing a second retinoblastoma tumour or other cancers, compared to those with heritable retinoblastoma.

What is heritable or hereditary cancer?

Heritable or hereditary cancer makes up about 5-10% of all cases of cancer. Some genes function to protect us from cancer. When they are not working well, it causes hereditary cancer. We refer to genes that are not working well as faulty genes.

Individuals who carry a faulty cancer gene(s) have a higher chance of developing certain cancers over their lifetime compared to the general population. The types of cancers that they may be at increased risk of will depend on the gene(s) involved.

If you have a faulty cancer gene, you may be at increased risk of developing certain cancers. As genes are shared among family, other family members may have inherited the faulty gene and may be at increased risk of cancer too.

What is genetic testing?

Genetic testing is offered to individuals where a hereditary cause of their personal and/or family history of cancer is suspected.

Genes contain the instructions that our body reads to carry out different functions. Genetic testing involves analysing your genes to understand if there are faults (i.e., mutations) that may increase the risk of diseases like cancer.

How is genetic testing done?

Genetic testing is typically a one-time blood test.
If a blood sample cannot be taken, other sample sources (e.g., skin or saliva) may be used.

What are the possible results of genetic testing?

There are 3 types of results you may receive:

Positive	Uncertain - Variant of Uncertain Significance (VUS)	Negative
Faulty gene(s) identified	Uncertain gene change(s) identified, unclear if these change(s) increase risk for tumours and cancers	No faulty gene(s) identified
Increased risk of developing certain tumours and cancers (depends on faulty gene(s) involved)	May be clarified by testing other family members	Tumour and cancer risk is similar to that of general population
Your family (parents, siblings, children and extended relatives) may have inherited the faulty gene(s) and should consider genetic testing to clarify this	May be reclassified over time as ‘positive’ or ‘negative’ when more information is known	Test limitations will be explained in the context of your personal and family history of tumours and cancers