This chart shows the likelihood that a parent will give retinoblastoma to a child.
Ninety percent of all children who develop retinoblastoma are the first person in their family to have eye cancer. It is hard to explain how a child with no family history develops retinoblastoma. In these cases, both parents are encouraged to have a complete eye exam.
When there is a family history of retinoblastoma, a child is most likely to develop the disease within 28 months of birth. Newborn babies should have a dilated eye exam by a pediatric ophthalmologist in the nursery.
When retinoblastoma is passed from parent to child, the child usually develops retinoblastoma in both eyes.
If a parent had retinoblastoma in one eye, 7 to 15 percent of his or her offspring will have retinoblastoma. Of those children, 85 percent will develop retinoblastoma in both eyes.
If a parent has been treated for retinoblastoma in both eyes, almost half (45 percent) of his or her children will develop retinoblastoma. Tumors in the eye may be present at birth, or may even be detected before birth.
However, many of these children do not have a tumor at birth. In our experience, if a child is going to develop retinoblastoma, he or she will begin to develop tumors by 28 months, but can continue to form them until the age of seven.
One percent of the time, there is evidence of a cured or limited form of retinoblastoma in a parent who was never aware of having had the disease and was never treated for it. In this case, 45 percent of that parent’s children will develop retinoblastoma.
More confusing, and rarer, is the possibility that a parent has the gene for retinoblastoma but no evidence of retinoblastoma in the eyes. This is called the carrier state, meaning the parent carries the gene but does not have the disease. Again, 45 percent of that parent’s children will develop retinoblastoma.
Although it is not exactly understood why people get retinoblastoma, we know that in all cases this cancer is caused by a missing or faulty piece of chromosome 13.
Chromosomes are the parts of a cell that contain genetic information. Chromosome 13 controls cell division in the retina. In children with retinoblastoma, this cell division continues unchecked, causing tumors in the retina.
In 60 percent of retinoblastoma cases, the abnormality is found only in eye cells; in 40 percent of cases, the abnormality is in every cell of the body, including the eye.