Ninety percent (90%) of all children who develop retinoblastoma are the first one in their family to have eye cancer. In 10% of retinoblastoma cases, however, a parent, grandparent, sibling, uncle, aunt, or cousin also had retinoblastoma. When retinoblastoma is passed from parent to child, the disease is usually, but not always, bilateral. Much work has been done in the past 10 years to figure out how a genetic abnormality causes cancer.

Although it is not exactly understood why retinoblastoma occurs, it is known that in all of the cases this cancer is caused by an abnormality in chromosome 13, in which a piece of the chromosome is nonfunctional or missing. In 40% of the cases, the abnormality is present in every cell of the body including the eye and in 60% of cases, the abnormality is only found in the eye. Chromosome 13 is responsible for controlling retinal cell division. In children with retinoblastoma, retinal cell division continues unchecked, causing the retinal tumor(s).

If a parent had bilateral retinoblastoma:

If a parent has been treated for bilateral retinoblastoma and decided to have children, almost half (45%) of their children will develop retinoblastoma in their eyes. The child may have tumors in the eye at birth and may even have tumors that have spread through the body and into the brain at birth. On the other hand, many of these children do not have tumors in the eye at birth and develop them during the first few years of life. In our experience, all of these children begin to develop tumors in the eyes by 28 months and can continue to form them until the age of 7 years.

The overwhelming majority of children born to a parent with bilateral retinoblastoma will also have bilateral retinoblastoma, but about 15% will develop tumors in only one eye (unilateral retinoblastoma). Every time the bilateral retinoblastoma parent has another child, the chance of that child developing retinoblastoma is 45%.

If a parent had unilateral retinoblastoma:

If a parent had unilateral retinoblastoma, 7% to 15% of their offspring will have retinoblastoma. Interestingly, when a parent with unilateral retinoblastoma has a child who develops retinoblastoma, that child will usually (85% of the time) develop bilateral retinoblastoma. Many of these affected children do not have the tumor present at birth. But as with the situation above, if the child is going to develop retinoblastoma, they will begin to develop tumors by 28 months and can continue to form them for 7 years.

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