Childhood Cancer

Childhood Cancer

Who gets retinoblastoma?

Retinoblastoma is usually diagnosed in very young children, and may be present at birth. In fact, over 95 percent of children are diagnosed before they are 5 years old. Approximately 350 children are diagnosed with retinoblastoma every year in the United States. There is no higher incidence in any particular race, and boys are affected as often as girls.

There are hereditary and non-hereditary forms of this disease. At diagnosis, 60 percent of children have a single tumor in one eye (unilateral retinoblastoma) and 40 percent have multiple tumors in one or both eyes (bilateral retinoblastoma). Unilateral retinoblastoma tends to be non-hereditary, whereas bilateral retinoblastoma is usually hereditary. Children with bilateral retinoblastoma are typically diagnosed at a younger age than those with only one tumor and one eye involved.

John Allen was 15 months old when he was diagnosed with unilateral retinoblastoma. The doctor didn’t give us any information other than it was a fast-growing cancer and that it needed to be taken care of right away. We couldn’t see the specialist for another 5 days, so we cried and prayed. We didn’t know whether we were going to lose our baby or not. When we saw the specialist, she answered all of our questions in detail. We were then referred to a pediatric oncologist and pediatric ophthalmologist surgeon. They, too, were fantastic. We were relieved when they explained the enucleation [removal of the eye] to us. What mattered most was that our little boy had an excellent chance of beating his disease.

Children who have the hereditary form of retinoblastoma and have disease in both eyes have a very small risk of also developing a tumor in the pineal gland of the brain, called pineoblastoma. Sometimes this is referred to as trilateral retinoblastoma.

Genetic factors

The exact cause of retinoblastoma is unknown. However, much is known about the genetics and inheritance of this tumor.

A change, called a mutation, in a gene called RB1 is involved in the development of retinoblastoma. Genes are located and organized on chromosomes inside the body’s cells. They are passed from parent to child through the egg and the sperm. The nuclei of human cells contain 22 chromosomes plus the sex chromosomes X and Y. There are two copies of each of these chromosomes, except for the sex chromosomes. Children get one copy of each of the 22 chromosomes from their biological mother and the other copy from their biological father.

The genes on these chromosomes contain material called DNA. The DNA instructs the cells to make proteins that determine such things as eye color, skin color, and blood type.

The RB1 gene is located on chromosome 13. In roughly 60 percent of children with retinoblastoma, there is a change in both copies of the RB1 gene, but only in the cells of the tumor in the eye. If you look at cells from any other area in the body, chromosome 13 is completely unchanged with no mutation in the RB1 gene. Scientists don’t know what causes the mutation in this gene. Most of the time, these children develop one tumor only in one eye. This is called the non-hereditary form of the disease (see table below on inheritance of retinoblastoma).

The hereditary form of retinoblastoma occurs in around 40 percent of children with the disease. In these cases, the mutated RB1 gene is found in all the cells of the body. In 85 percent of children with the hereditary form of retinoblastoma, no one else in the family has retinoblastoma (called the non-familial or sporadic form). In these cases, a spontaneous mutation occurs in the copy of the RB1 gene when the child is conceived. The parents do not carry a mutation of the RB1 gene in every cell of their bodies.

The remaining 15 percent of children with the hereditary form of retinoblastoma have a family member with the disease (usually a parent). This is called the familial form. In these cases, a parent had an abnormal copy of the RB1 gene in every cell in his or her body and passed it on to the child through the sperm or egg. All of these children started their lives with one mutated copy of the RB1 gene in every cell in their bodies, including all the retinoblasts in the eye. After conception, if a mutation occurs in the other copy of the RBI gene in one or more retinoblasts in the eye, retinoblastoma develops. In these children, the disease can occur in one or both eyes and more than one tumor may be present at diagnosis. New tumors may form during the first 5 years of life.

Non-hereditary form
Approximately 60% of all children diagnosed
Hereditary form
Approximately 40% of all children diagnosed
  Non-familial form (85%) Familial form (15%)
Child usually has one tumor in one eye No family history of retinoblastoma Family history of retinoblastoma
Mutation is found only in tumor cells Spontaneous mutation is found in all cells of body Inherited mutation is found in all cells of body
Survivors cannot pass mutation on to offspring Survivors can pass mutation on to offspring (50% risk for each child) Survivors can pass mutation on to offspring (50% risk for each child)

It is not known what causes the changes in the RB1 gene in either of these forms of retinoblastoma. It is known that there is nothing parents can do to prevent retinoblastoma.

I am a long-term survivor of bilateral retinoblastoma, diagnosed when I was 10 months old. My first enucleation [surgical removal of the eye] was the left eye in May 1971, with radiation to the right eye. The enucleation of the right eye was in March 1972. I have had no subsequent treatment since then. Due to my loss of sight at such an early age, I had no traumatic adjustment period that losing sight later in life might have caused. I really can think of no significant effects that my retinoblastoma has had on my adult life other than the usual adaptations required for dealing with blindness.

Pediatric oncologists help determine whether the disease is hereditary or non-hereditary based on a number of factors, including family history, age at diagnosis, number of tumors, and whether one or both eyes are involved. They will then discuss the benefits of genetic testing to verify whether your child has the hereditary or non-hereditary form of the disease. Genetic testing and counseling should be offered to all families of children with retinoblastoma.

If the pediatric oncologist has not told you which type of retinoblastoma your child has, you should ask. The oncologist can then explain whether other family members need to be checked for retinoblastoma and how often.

The type of retinoblastoma your child has affects:

•  Treatment options

•  Risk for having another child with retinoblastoma

•  Risk of your child having a child with retinoblastoma

•  Risk of your child getting other cancers later in life

Children with the hereditary form of retinoblastoma are at a higher risk of getting another cancer later in life than children with the non-hereditary form of the disease are.

Environmental factors

When Westley was diagnosed with retinoblastoma at 7 months old, our ophthalmologist immediately ordered genetic testing to determine if he had the hereditary form of the disease and if he had inherited a mutation from my husband, who was diagnosed with unilateral retinoblastoma 35 years ago when he was 18 months old. Westley was found to have bilateral, hereditary retinoblastoma, with multiple tumors in both eyes.

When my husband was diagnosed with retinoblastoma, they removed his eye and he was examined every 6 months until he was 5 years old. He didn’t have chemotherapy or radiation, and he never had any more tumors. He had multiple prosthetics because he would hide or flush his eye down the toilet sometimes when he was a grumpy toddler. Now he gets a new one every 10 years.

I am bothered by the fact that even though we had amniocentesis and genetic testing when I was pregnant with Westley because I was 35, and they knew my husband was a retinoblastoma survivor, no one warned us of the genetic risk to our child and that we should have him examined carefully by his pediatrician to watch for signs of tumors in his eyes. Since he was diagnosed, we have had good genetic counseling. Sometimes my husband feels guilty that he passed this on to our son, but we know that no one is to blame. Because of the high risk of having another child with retinoblastoma, we have decided not to have any more biological children.

No environmental factors have been linked to increased risk of retinoblastoma.