Retinoblastoma

Overview

Retinoblastoma is a rare cancer of the retina, the thin layer of light- and color-sensing tissue that lines the back of the eye. Retinoblastoma usually develops in childhood, almost always before the age of 5 years, and usually before age 2. 

Retinoblastoma can cause blindness and is life-threatening if it spreads to other parts of the body. Fortunately, thanks to earlier diagnosis and improved treatment, survival rates for retinoblastoma are now about 95 percent.

Causes

Retinoblastoma is caused by mutations in the RB1 gene. Like all genes, we have two copies of the RB1 gene in each of our cells — one inherited from our father and one from our mother. If a child inherits a mutated RB1 gene from one parent, then every cell in his or her body has that mutation in one copy of the gene. This is called a "germline" or "heritable" mutation. If the second copy of the gene mutates in a cell, a tumor will develop there.

Children with germline mutations tend to develop several retinoblastomas, usually in both eyes. They can also develop tumors in the brain, bone, lungs and other parts of the body. Furthermore, each of their children will have a one-in-two chance of inheriting the mutation; among the children who inherit the mutation, almost all will develop retinoblastoma.

If the mutation first occurs in a person's egg or sperm cell, then the other cells of the body will not carry the mutation and there is no risk of developing retinoblastoma. However, that person's children will each have a one-in-two chance of inheriting the mutation.

If the mutation occurs during early fetal development (before birth), only some of the cells in the body will carry the mutation. This is called "mosaicism."

If both RB1 genes spontaneously mutate in the same retinal cell, then only one tumor develops and all the other cells of the body are unaffected. Since the mutation does not involve the eggs or sperm, this is called a "somatic" mutation. Somatic mutations are not passed on to the person's children.

Signs & symptoms

Retinoblastoma is usually discovered when someone notices that the child's pupil appears white instead of black when the light catches it from a certain direction or when a photograph is taken with a flash. In some children, the disease is detected because the eye turns inwards or outwards. If the tumor is advanced, the eye can become inflamed and painful. When both eyes are affected, the child may have difficulty seeing.

Diagnosis

To diagnose retinoblastoma, an ophthalmologist will examine the back of the eye after dilating the pupil with drops. The size of the tumor is measured using ultrasound scans. Magnetic resonance imaging (MRI) is also performed to detect any tumors growing in the brain. These examinations are usually performed under general anesthesia.

The child will undergo genetic tests to identify the mutation and to find out whether the mutation is germline or somatic (that is, whether the mutation is present throughout the body or only in the retinoblastoma tumor in the eye). These tests are performed using a blood sample or a buccal smear, a gentle scraping from the lining of the mouth. If the eye needs to be removed, a pathologist will also analyze a tumor sample.

If the child is found to have a germline or "heritable" mutation, his or her parents will have the genetic testing done.

Treatment

If possible, small retinoblastomas located towards the back of the eye are treated by heating the tumor with a laser. Tumors near the front of the eye are destroyed by cryotherapy (freezing). Treatment needs to be repeated several times to ensure the tumor has been completely destroyed.

If the tumor is too large to be treated with lasers or cryotherapy, chemotherapy is used. There are several methods for administering chemotherapy. The method we use depends on the location of the tumor or tumors.

• Systemic chemotherapy is injected and spreads through the bloodstream to the entire body. It is used to treat both eyes at the same time as well as any possible or definite tumors in other parts of the body.
• With intra-arterial chemotherapy, a long, narrow tube is gently inserted into a small incision in the groin, then passed through blood vessels in the the chest and neck and into a tiny artery behind the eye. Intra-arterial therapy is used to treat only one eye.
• In intra-vitreal chemotherapy, the chemotherapy drug is injected directly into the middle of the eye. This is used if the tumor has scattered cancerous cells into the vitreous cavity (the space between the lens and the retina).

No matter which method is used, chemotherapy needs to be repeated several times, usually at monthly intervals.

If the chances of saving the eye are too small to justify exposing the child to chemotherapy and many anesthetics, the eye is removed. This operation is called "enucleation." When the eye is removed, a ball implant is buried in its place. The ocular muscles are sewn to this implant so that the artificial eye moves normally. Then, a contact lens-like prosthesis is custom made to match the color of the other eye. The prosthesis is fitted to the implant about six weeks after the enucleation.

Although it can sound frightening to parents, babies and young children often cope with enucleation remarkably well.

After the eye is removed, a pathologist will examine it to estimate the risk of retinoblastoma spreading (or "metastasizing") to other parts of the body. The risk of metastasis is higher if the tumor has spread beyond the retina into the optic nerve, the choroid (the blood-filled layer beneath the retina), or into the tissues outside the eye. Children with an increased risk of metastatic disease are treated with systemic chemotherapy as a precaution.

After-Care

After treatment, children need to have frequent eye exams — usually every month until the age of 2 years, then less frequently until the age of 5, then every six months until the age of 9, and then once a year. These examinations are performed to detect any new or recurrent tumors when they are still very small and easier to treat.

The Care Team

At UCSF's Retinoblastoma Program, patients are cared for by a large team that includes ocular oncologists, pediatric oncologists, specialist nurses, interventional radiologists, social workers and other experts. We take special measures to ensure that parents have all the knowledge and support they need to achieve the best possible outcome for their child.