The retina is the inner layer of your eye where light-detecting cells gather information and send a signal to the brain via the optic nerve to produce visual perception. Retinoblastoma is a very rare type of cancer that forms when immature retinal cells (retinoblasts) grow out of control. Retinoblastoma almost always develops in children, and less than 500 cases are diagnosed in the U.S. each year. If left untreated, it may be life-threatening.
What Causes Retinoblastoma?
Retinoblastoma is caused by a mutation in the tumor-suppressing RB1 gene. RB1 gene mutations may occur before birth, resulting in congenital (heritable) retinoblastoma. When a second RB1 mutation occurs during childhood, multiple tumors may develop in both eyes.
Because the RB1 gene mutation was either inherited from a parent or developed just after fertilization, it is present in every cell. There is an increased risk of developing many other types of cancer in children diagnosed with congenital retinoblastoma, including bone marrow and liver cancer.
RB1 gene mutations that occur in the retina during childhood result in sporadic retinoblastoma. Because the mutated tumor-suppressing RB1 gene only exists in the retinal cells of one eye, only one tumor forms. Sporadic retinoblastoma is not associated with an increased risk of cancer in other parts of the body.
Both types of retinoblastoma can metastasize and spread to distant sites.
How Is Retinoblastoma Diagnosed?
Early detection is key to reducing the quality of life impacts experienced by children diagnosed with retinoblastoma. Because retinoblastoma affects the immature retinal cells that are present during prenatal development and early childhood, it’s important to treat cancer as soon as possible.
Children with retinoblastoma often exhibit symptoms that demand further investigation. The most common early sign is the “cat’s-eye reflex” or leukocoria which shows up as a white, pink, or yellow flash in the pupil of the eye. Other symptoms may include impaired vision, crossed eyes or eyes that don’t point in the same direction and (in advanced cases) enlargement of the eye.
Because biopsy of the tumor presents a high risk of damaging the eye or spreading cancer cells, it’s diagnostic use is limited. Most of the time, a detailed examination under an ophthalmoscope is enough to confirm the diagnosis of retinoblastoma. This procedure is usually performed with the child under anesthesia.
If evidence of retinoblastoma is found during examination imaging by MRI, CT, or ultrasound will be performed to confirm the diagnosis and assess whether or not cancer has spread to other structures of the eye or metastasized. In rare cases, a spinal tap may be utilized to see if cancer has spread to the optic nerve or brain. During treatment, changes within the eye will be monitored through the use of these diagnostic techniques to determine the effectiveness of treatment.
A blood test can help determine if the child has congenital retinoblastoma. Because the RB1 tumor-suppressing gene mutation shows up in every cell, it is detectable in the blood. In cases where inherited retinoblastoma is suspected, families are often advised to undergo genetic testing themselves to assess increased cancer risks related to carrying the mutation.
The most common first-line treatment for retinoblastoma is chemotherapy. Drugs designed to target and kill cancer cells are administered intravenously, through direct injection into the eye, via an artery or through an oral route. Chemotherapy is used to shrink a tumor before other, more aggressive or targeted treatments are called upon.
Focal therapy involves the use of a laser or a freezing therapy (cryotherapy) to irradicate the tumor. Sometimes a tumor is small enough to treat with focal therapies alone, but it is common as a second-line treatment after chemotherapy.
If the cancer is not responsive to focal treatments and chemotherapy, the next course of action is usually radiation therapy.
Two forms of radiation treatment are employed to fight retinoblastoma: internal and external radiation. During internal radiation treatment, a small radioactive plaque may be stitched into place near the tumor and left to emit radiation for a few days before being removed. Healthy tissues are less likely to be affected by radiation during internal radiation treatments.
During external radiation treatment, radiation is delivered from multiple angles by a large machine. The healthy tissues of the eye and brain. External radiation treatment is associated with an increased risk of side-effects and is usually reserved for advanced or unresponsive cases.
Removing cancer through surgery is often a last-line treatment measure. When cancer has grown too large, begun to metastasize, or the eye has lost vision due to damage enucleation (removal of the eye and optic nerve) may be required. An orbital implant is typically put in place and attached to the muscles that move the eye. Later, the child can be fitted with an artificial eye that will not provide sight but will appear almost identical to their natural eye.
The 5-year survivorship rate of children with localized retinoblastoma is 95%. In most cases of sporadic retinoblastoma, the risk of recurrence is small. Children with congenital retinoblastoma will require ongoing screening for recurrence as well as the development of other types of cancer. In cases where the child loses one or both eyes, they can live full, independent lives despite vision loss or impairment.