Rb Fast Facts
Introduction to Rb
Global Incidence
Signs and Symptoms
Referral and Diagnosis
Staging Systems
Exam Under Anaesthetic
Treatment Options
Clinical Trials
Follow Up and Prognosis
RB1 Genetics
Glossary Of Terms
retino - means of the retina.
blast - means an immature cell.
oma - means a swelling or tumour.
Retinoblastoma is a tumour which arises from immature cells of the retina. The retina is,the light-sensitive layer of cells at the back of the eye, which converts light into nerve signals.
Sometimes, the parents or brothers and sisters of a child with retinoblastoma are found to have a retinoma, a benign precursor that has somehow stopped growing. This shows the parent carries a constitutional RB1 mutation, but never developed retinoblastoma themselves.
All types of retinoblastoma are highly malignant, but some tumours grow more aggressively than others, depending on the unique molecular changes that initiated the them. Tumours grow much faster in infants as the whole baby is growing rapidly. New tumour growth in a child of two years old progresses comparatively slowly.
Unilateral retinoblastoma
In about 65% of cases, only one eye is affected, and this is known as unilateral retinoblastoma. In developed countries, the average age at diagnosis is 18 months. In developing countries, children are often diagnosed at a much later age, due to poor access to informed healthcare providers.
Unilateral retinoblastoma usually involves just one tumour, but some children develop more than one tumour in one eye (known as multifocal unilateral retinoblastoma). Children with more than one tumour in one eye are generally thought to have a constitutional RB1 mutation. However, it is sometimes difficult to differentiate between true multifocal retinoblastoma and seeds which have developed from a single tumour. Seeds are small fragments of tumour that have broken away from the main tumour.
About 83% of children with unilateral retinoblastoma have the non-heritable form, but genetic testing is the only way to identifty heritable cancer in children with just one affected eye. When the child is under 12 months old at diagnosis, the likelihood that the child has a constitutional RB1 mutation is higher, and it is possible for tumours to develop in the other eye some weeks or months after the initial diagnosis. However, the risk reduces with age, and children older than three years of age, with a known or suspected constitutional RB1 mutation, are considered to be at very low risk of developing tumours in the second eye.
Bilateral retinoblastoma
Approximately 35% of children with retinoblastoma develop tumours in both eyes. This is known as bilateral retinoblastoma. A child who is initially diagnosed with unilateral retinoblastoma may later develop tumours in the other eye, when the diagnosis becomes bilateral. However, retinoblastoma does not spread from one eye to the other. If the cancer does develop in both eyes, each new tumour arises from a unique retinal cell.
All children with bilateral tumours have a constitutional RB1 mutation, which may have been inherited from a parent. In the developed world, bilateral retinoblastoma is most commonly diagnosed within the first twelve months of life, and 50% of babies with a known risk are born with tumours already formed.
When both eyes are affected, multiple tumours usually develop in each eye, and most children with bilateral retinoblastoma develop between 4-10 tumours in total between both eyes. The risk of new tumour growth diminishes significantly after three years of age. However, the risk of re-growth in old tumours remains for several years after the last tumour activity. Risk of recurrence depends on the size and location of tumours, the unique molecular changes in the RB1 gene that initiated them, and the type and quantity of previous treatment.
Extraocular Retinoblastoma
If retinoblastoma is not diagnosed promptly and treated effectively, cancerous cells can spread beyond the eye. This is known as extraocular or matastatic retinoblastoma. Retinoblastoma usually spreads along the optic nerve to the brain, cerebrospinal fluid (fluid bathing the brain and spine) and meninges (the lining of the brain), or through blood vessels to the eye socket, bone marrow or lymph nodes in the neck.
Risk factors for extraocular retinoblastoma include:
• delayed diagnosis and treatment
• tumour in the anterior segment (front of the eye)
• tumour covering the optic nerve head
• retinal detachment or ocular haemorrhage (bleeding in the eye) that
prevents thorough eye examination
• invasion of the choroid or sclera (outer layers of the eye)
• biopsy without complete removal of the eye.
If metastases develop after initial diagnosis, this usually happens within two years.
Tumour spread beyond the eye is extremely rare in developed countries. However, it is very common in resource-limited regions of the world, where diagnosis is frequently delayed, and optimal management is severely undermined by lack of comprehensive pathological examination of removed eyes, uncoordinated care and incomplete follow-up.
Trilateral retinoblastoma
Rarely, a separate tumour develops deep in the brain of a child with a constitutional RB1 mutation. This should not be confused with extraocular retinoblastoma involving the brain or spine.
This brain tumour is most commonly known as trilateral retinoblastoma (TRb), because most affected children also have tumours in both eyes. However, trilateral retinoblastoma can also affect children who have a constitutional RB1 mutation but cancer in only one eye , and carriers of a constitutional RB1 mutation who have not developed eye tumours.
Other names for trilateral retinoblastoma include ectopic intracranial retinoblastoma, primitive neuroectodermal tumour (PNET) or pineoblastoma (referring to the cell type), pineal retinoblastoma or suprasellar retinoblastoma (referring to the location).
Trilateral tumours usually occur 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 region TRb.
Trilateral retinoblastoma affects approximately 5% of children with a constitutional RB1 mutation. The brain tumour may be identified at the same time as diagnosis of eye tumours, or some time after initial diagnosis and treatment. Intracranial tumours usually occur within 3 years of the original ocular 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.
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 chemotherapy as the principal treatment for bilateral retinoblastoma.
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