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 they carry a mutated RB1 gene, but never developed retinoblastoma themselves.
When there is no family history of retinoblastoma, the cancer is referred to as “sporadic”, but it can still be passed on to the next generation if the patient has a heritable RB1 mutation.
All types of retinoblastoma are highly malignant, but some tumours grow more aggressively than others, depending on the unique molecular changes which initiated the cancer. Tumours grown 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, most children with unilateral retinoblastoma are diagnosed between two to two-and-a-half years of age, and the average age at diagnosis is 28 months. In developing countries, children are often diagnosed at a later age, due to poor access to informed healthcare providers.
About 17% of children with unilateral tumours have the heritable form of retinoblastoma, but genetic testing is the only way to identify heritable cancer in children with just one affected eye, when there is no prior family history of retinoblastoma.
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 heritable retinoblastoma. 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.
When the child is under 12 months old at diagnosis, the likelihood of heritable retinoblastoma is higher, and it is possible for tumours to develop in the other eye some weeks or months after the initial diagnosis. This risk reduces with age, and children older than three years of age, with a known or suspected heritable 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, and this is known as bilateral retinoblastoma. Retinoblastoma does not spread from one eye to the other, and if the cancer does develop in both eyes, each new tumour arises from unique retinal cells.
All children with bilateral tumours have heritable retinoblastoma, 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. A child who is initially diagnosed with unilateral retinoblastoma at a young age may later develop tumours in the other eye, and in this situation, the diagnosis becomes bilateral.
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 does not diminish until two years after the last tumour activity. Risk of recurrence depends on the type and quantity of previous treatment, size and location of tumours, but is not significantly related to the age of the child.
Trilateral retinoblastoma
A separate tumour can develop deep in the brain of a child with heritable retinoblastoma. This brain tumour is most commonly known as trilateral tetinoblastoma (TRb), because most affected children also have tumours in both eyes. However, trilateral retinoblastoma can equally affect children with heritable unilateral retinoblastoma, or carriers of a heritable RB1 mutation who have not developed eye tumours.
Other names for this tumour include ectopic intracranial retinoblastoma, primitive neuroectodermal tumour (PNET) or pineoblastoma (referring to the cell type), pineal retinoblastoma or suprasellar retinoblastoma (referring to the location). To avoid confusion, throughout this website, we refer to this tumour simply as “trilateral retinoblastoma" or "TRb".
Trilateral retinoblastoma is a primary tumour, and should not be confused with extraocular retinoblastoma involving the brain or spine. 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 TRb usually develops at an earlier age than pineal TRb, 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 heritable retinoblastoma. The 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.
The incidence of trilateral retinoblastoma diagnosed following treatment for eye tumours appears to have decreased in recent years. This is most likely due to introduction of chemotherapy as the principal treatment for bilateral retinoblastoma, and the elimination of radiotherapy, which can induce trilateral tumours in this group of patients.
Children with isolated pineoblastoma or suprasellar PNET may develop tumours in one or both eyes some time after diagnosis of the brain tumour.
Extraocular Retinoblastoma
If retinoblastoma is not diagnosed promptly and treated effectively, cancerous cells can spread beyond the eye, or recur in the socket following removal of the eye. This is known as metastatic or axtraocular retinoblastoma. In this instance, 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 bones, bone marrow or lymph nodes in the neck.
Risk factors for extraocular retinoblastoma include delayed diagnosis and treatment, glaucoma (high pressure in the eye), a bulging eye, tumour in the anterior segment (front of the eye), tumour covering the optic nerve head, retinal detachment or ocular haemorrhage that prevents thorough eye examination, invasion of the choroid or sclera (outer layers of the eye), and biopsy without complete removal of the eye.
If extraocular retinoblastoma develops after initial diagnosis, this almost always happens within two years of first diagnosis.
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 severely undermined by lack of comprehensive pathological examination of removed eyes, uncoordinated care, poor family support and incomplete follow-up.
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