What should you know about Knudson's two-hit hypothesis and retinoblastoma?

A gene called RB1 normally helps restrain cell growth. In the two-hit model, the first change may be present from birth in every cell, or it may arise only in a retinal cell. A second change affecting the remaining working copy can remove that growth control in the cell. The altered cell may then multiply and form retinoblastoma.

When the first change is inherited, it can affect both eyes or lead to more than one tumour focus, and it may have implications for relatives. When both changes arise within one retinal cell, the disease is generally limited to that cell lineage. This model describes a biological pathway; it does not by itself determine a child's outlook or select one treatment.

If retinoblastoma has been diagnosed, ask whether genetic counselling and RB1 testing are appropriate. Testing can help clarify whether a change may be inherited and whether close relatives or future children could need advice. The clinical team may combine eye examinations, imaging, and family history when planning care.

Treatment is chosen according to the number, size, and position of tumours, vision concerns, and whether disease is confined to the eye. Options may include local treatment, chemotherapy, or selected radiation approaches such as brachytherapy. A genetics result should be explained alongside the child's examination findings.

Arrange prompt assessment for a child with a white reflection in the pupil, a new eye turn, a red or painful eye, reduced vision, or an eye that appears enlarged. These signs have several possible causes, but retinoblastoma needs timely specialist assessment because the eye and vision are developing.

Seek urgent medical help if severe eye pain, sudden vision change, marked swelling, or injury occurs. Do not wait for genetic testing before reporting a new eye symptom.

Ask: Does the child's result suggest an inherited RB1 change? Should parents or siblings receive counselling or testing? What examinations are needed for the other eye? Which treatment aims to protect vision, and how will treatment be monitored?