Rarely, a primary tumour develops deep in the brain of a child with a constitutional RB1 mutation.
This should not be confused with extraocular or metastatic retinoblastoma – cancer that has spread from the eye to the brain due to delayed diagnosis, inappropriate or incomplete treatment.
Other names for trilateral retinoblastoma include:
- ectopic intracranial retinoblastoma
- primitive neuroectodermal tumour (PNET)
- pineoblastoma or pineal retinoblastoma
- suprasellar retinoblastoma
Types of Trilateral Retinoblastoma
Trilateral retinoblastoma usually occurs in or adjacent to the pineal gland. Suprasellar and parasellar tumours arise in the region of the pituitary gland and the third ventricle.
Suprasellar retinoblastoma usually develops at an earlier age than pineal retinoblastoma, and heritable unilateral retinoblastoma is possibly more commonly associated with suprasellar TRb than with pineal TRb.
Children at Risk of Trilateral Retinoblastoma
This primary brain tumour is most often called trilateral retinoblastoma (TRb), because most affected children also have cancer in both eyes. However, trilateral retinoblastoma can affect children with a constitutional RB1 mutation but cancer in only one eye. Carriers of a constitutional RB1 mutation who have not developed eye tumours can also develop trilateral retinoblastoma.
The brain tumour may be identified at the same time as diagnosis of eye tumours, or some time later.
Intracranial tumours usually occur within 3 years of the original retinoblastoma diagnosis, and are rarely diagnosed more than 5 years from initial diagnosis.
Children with isolated pineoblastoma, suprasellar or parasellar PNET may develop tumours in one or both eyes some time after diagnosis of the brain tumour.
Incidence of Trilateral Retinoblastoma
Trilateral retinoblastoma affects approximately 5% of children with a constitutional RB1 mutation.
The incidence of trilateral retinoblastoma diagnosed following treatment for eye tumours appears to have decreased in recent years. This is most likely due to
- the reduced use of radiotherapy, which can induce trilateral tumours, and
- introduction of systemic chemotherapy as the principal treatment for bilateral retinoblastoma, which may kill trilateral tumours before they are discovered.