Retinoblastoma is a rare type of eye cancer that usually develops in early childhood, typically before the age of 5. This form of cancer develops in the retina, which is the specialized light-sensitive tissue at the back of the eye that detects light and color.
In most children with retinoblastoma, the disease affects only one eye. However, one out of three children with retinoblastoma develops cancer in both eyes. The most common first sign of retinoblastoma is a visible whiteness in the pupil called "cat's eye reflex" or leukocoria. This unusual whiteness is particularly noticeable in photographs taken with a flash. Other signs and symptoms of retinoblastoma include crossed eyes or eyes that do not point in the same direction (strabismus); persistent eye pain, redness, or irritation; and blindness or poor vision in the affected eye(s).
Retinoblastoma is often curable when it is diagnosed early. However, if it is not treated promptly, this cancer can spread beyond the eye to other parts of the body. This advanced form of retinoblastoma can be life-threatening.
When retinoblastoma is associated with a gene mutation that occurs in all of the body's cells, it is known as germinal retinoblastoma. People with this form of retinoblastoma also have an increased risk of developing several other cancers outside the eye. Specifically, they are more likely to develop a cancer of the pineal gland in the brain (pinealoma), a type of bone cancer known as osteosarcoma, cancers of soft tissues such as muscle, and an aggressive form of skin cancer called melanoma.
Retinoblastoma is diagnosed in 250 to 350 children per year in the United States. It accounts for about 4 percent of all cancers in children younger than 15 years.
Mutations in the RB1 gene are responsible for most cases of retinoblastoma. RB1 is a tumor suppressor gene, which means that it normally regulates cell growth and keeps cells from dividing too rapidly or in an uncontrolled way. Most mutations in the RB1 gene prevent it from making any functional protein, so it is unable to regulate cell division effectively. As a result, certain cells in the retina can divide uncontrollably to form a cancerous tumor. Some studies suggest that additional genetic changes can influence the development of retinoblastoma; these changes may help explain variations in the development and growth of tumors in different people.
A small percentage of retinoblastomas are caused by deletions in the region of chromosome 13 that contains the RB1 gene. Because these chromosomal changes involve several genes in addition to RB1, affected children usually also have intellectual disability, slow growth, and distinctive facial features (such as prominent eyebrows, a short nose with a broad nasal bridge, and ear abnormalities).
Researchers estimate that 40 percent of all retinoblastomas are germinal, which means that RB1 mutations occur in all of the body's cells, including reproductive cells (sperm or eggs). People with germinal retinoblastoma may have a family history of the disease, and they are at risk of passing on the mutated RB1 gene to the next generation. The other 60 percent of retinoblastomas are non-germinal, which means that RB1 mutations occur only in the eye and cannot be passed to the next generation.
In germinal retinoblastoma, mutations in the RB1 gene appear to be inherited in an autosomal dominant pattern. Autosomal dominant inheritance suggests that one copy of the altered gene in each cell is sufficient to increase cancer risk. A person with germinal retinoblastoma may inherit an altered copy of the gene from one parent, or the altered gene may be the result of a new mutation that occurs in an egg or sperm cell or just after fertilization. For retinoblastoma to develop, a mutation involving the other copy of the RB1 gene must occur in retinal cells during the person's lifetime. This second mutation usually occurs in childhood, typically leading to the development of retinoblastoma in both eyes.
In the non-germinal form of retinoblastoma, typically only one eye is affected and there is no family history of the disease. Affected individuals are born with two normal copies of the RB1 gene. Then, usually in early childhood, both copies of the RB1 gene in retinal cells acquire mutations or are lost. People with non-germinal retinoblastoma are not at risk of passing these RB1 mutations to their children. However, without genetic testing it can be difficult to tell whether a person with retinoblastoma in one eye has the germinal or the non-germinal form of the disease.
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- Glioma, retinal