Retinoblastomas
Retinoblastoma is a rare type of cancer that affects the retina, the light-sensitive layer at the back of the eye, primarily in young children. There are two forms of the disease: bilateral, which affects both eyes and is often hereditary, and unilateral, which affects one eye and is typically sporadic. The condition usually presents with symptoms such as leukocoria (a white reflection in the pupil), strabismus (crossed eyes), and vision issues. It generally occurs in children under the age of five, with the average diagnosis around 18 months.
Risk factors include a family history of the disease, and those with bilateral retinoblastoma face a higher risk of developing secondary cancers later in life. Diagnosis is confirmed through various imaging techniques and genetic testing, while treatment options range from local therapies for small tumors to chemotherapy and radiation for more advanced cases. The survival rate is high when the cancer is detected early, with five-year survival rates between 96% and 99% in developed countries. Though the genetic nature of retinoblastoma means it cannot be prevented, prenatal testing can identify the defective gene, allowing for early interventions.
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Subject Terms
Retinoblastomas
ALSO KNOWN AS: Cancer of the retina
RELATED CONDITIONS: Second extraocular tumors or cancer, trilateral retinoblastomas (pineoblastomas)
DEFINITION: Retinoblastomas are rare cancers (malignant tumors) of the eye's retina in young children. The retina is the innermost light-sensitive layer of the eye wall and is responsible for vision. There are two types of retinoblastoma, bilateral (affects both eyes) and unilateral (affects one eye). The bilateral type is hereditary and accounts for about one in three children with retinoblastoma. Two out of three retinoblastoma cases are sporadic, non-hereditary, and unilateral.
Risk factors: The only known risk factor for retinoblastoma is a family history of the disease; however, the condition carries a risk of secondary cancer as it can spread outside the eye to other parts of the body. Children with the bilateral type have a higher risk of developing a second tumor, including a pineoblastoma. Retinoblastoma also places patients at risk of developing other types of cancer later in life.
Etiology and the disease process: During prenatal development of a child, the youngest cells (retinoblasts) divide and redivide to form the differentiated cells of the retina. Sometimes, mutations occur on the retinoblastoma 1 (RB1) gene, causing an abnormality in chromosome 13. This causes some retinoblasts to multiply uncontrolled, creating a tumor of undifferentiated cells: a retinoblastoma. Bilateral tumors generally develop earlier than unilateral ones. The uncontrolled tumor can fill the entire orbit, and glaucoma can develop, which can cause pain and vision loss. If the condition remains untreated, the cancer can spread through the brain and spinal cord and then to other parts of the body (secondary tumor).
Incidence: Between 200 and 300 children under the age of five are diagnosed with retinoblastoma in the United States per year, while the rate is higher in developing countries. The disease occurs equally in boys and girls and within all races. The rate of incidence is higher in infants (newborn to one year) and younger children, and lower in older children (between two and twelve years). About 80 percent of children diagnosed with the disease are younger than three, and 95 percent of cases are in children under five. The average age of diagnosis is eighteen months.
Symptoms: A common and early symptom is leukocoria, a white reflection in the pupil, often first noticed in flash photographs. Others include strabismus (crossed eyes), inflammation (red irritation and swelling) on the eyes, vision problems, and a glazed look on the eye.
Screening and diagnosis: The main screening by an ophthalmologist is to check for a normal red reflex in the eye (normally, blood vessels in the back of the eye reflect red). If a white reflex (cat’s-eye reflex) is observed, it is due to leukocoria. The doctor will also examine the corneal light reflex to check for strabismus and look for inflammation around the eyes or vision problems, including a decrease in vision. A blood test may be performed to check for deoxyribonucleic acid (DNA) mutations.
The diagnosis of retinoblastoma is confirmed by ophthalmoscopic examination, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) scans, and, if absolutely necessary, spinal tap and bone marrow biopsy.
The following are the three stages of retinoblastoma:
- Stage I: Intraocular; the tumor remains inside the eye.
- Stage II: Extraocular; the tumor spreads outside the eye or to another part of the body (second tumor).
- Stage III: Recurrent; cancer returns in the eye or another part of the body after being treated. The hereditary form of retinoblastoma can recur years after treatment.
Treatment and therapy: Treatment depends on the size of the tumor. For small tumors, local therapies such as laser photocoagulation, thermotherapy, and cryotherapy may be used. Chemotherapy (oral or intravenous) can also be used to kill cancer cells and shrink a tumor for local treatment. Intra-arterial chemotherapy is increasing used as this method of delivering chemotherapy directly to the eye has allowed for more positive outcomes. For more advanced retinoblastomas radiation therapy is used. Radiation therapy can consist of an external beam of X-rays or internal radiation (plaque and radial beam radiotherapy). In plaque radiotherapy, radioactive material is placed near the tumor to kill cancer cells. Immunotherapies and gene therapies have shown promise as well.
When all other treatments fail to control the tumor, pain, and blindness, enucleation, or surgical removal of the eye, is performed to save the child’s life.
Prognosis, prevention, and outcomes: The disease was nearly always fatal before the advent of modern technology, and the advanced metastatic form remains nearly 100 percent fatal. However, when detected and treated early, the five-year survival rate is between 96 and 99 percent in developed countries. The prognosis for vision retention and the development of a second tumor depends on the stage of the disease and treatment efficacy.
Because of its genetic component, retinoblastoma cannot be prevented. However, the defective gene can be detected in utero through tests of amniotic fluid, which allows for the option of terminating the pregnancy. Another option is in vitro fertilization, in which an embryo without the defective gene can be implanted in the womb.
Bibliography
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