Tests for Retinoblastoma

When a child is diagnosed with retinoblastoma, it is important to know if it is the heritable form or the non-heritable form of the disease because children with heritable retinoblastoma:

• Have an increased risk of developing other cancers later in life.
• Are more sensitive to radiation, thus radiation should be avoided.
• Need close follow-up after treatment.
• Have a 1 in 2 chance of passing the RB1 gene change on to each of their own children.
• May have other family members, such as brothers or sisters, who also carry the RB1 gene change.

If tumors are found in both eyes (bilateral retinoblastoma), it can be assumed that the child has heritable retinoblastoma (even if there is no family history of the disease). This means they carry the RB1 gene change in all their cells. Although, some children with retinoblastoma in only one eye might also have heritable retinoblastoma.

A blood test can be done to look for the RB1 gene change in cells outside the eye in children with retinoblastoma in one or both eyes. This test can usually tell if the child has the heritable form of retinoblastoma.

Sometimes tests cannot tell with certainty if a child inherited the RB1 gene change. In these cases, the safest plan is to watch the child (and other children in the family) closely for retinoblastoma with frequent eye exams.

If a child is suspected of having retinoblastoma that has spread to the bones, blood tests to check blood cell counts may be done as part of testing at diagnosis.

If part of the treatment plan for retinoblastoma includes chemotherapy, or an exam requires anesthesia, often doctors will do tests to make sure the body is healthy enough for the exam or treatment. These tests are usually blood and urine tests and check blood counts, liver function, kidney function, and the balance of salts (electrolytes) in the body.

Most children with retinoblastoma do not need a lumbar puncture. It is used when there is a reason to think retinoblastoma might have spread into the brain. Retinoblastomas can sometimes grow along the optic nerve, which connects the eye to the brain. If the cancer has spread to the surface of the brain, a lumbar puncture, sometimes called a spinal tap, can be done to collect cerebrospinal fluid (CSF). This is the fluid that surrounds the brain and spinal cord, and it can contain cancer cells.

Typically for this test, the child is given medicine (anesthesia) so they will be asleep and not move during the procedure. The doctor first numbs an area in the lower part of the back over the spine. A small, hollow needle is then placed between the bones of the spine to withdraw a small amount of the fluid, which is then sent to the lab for testing.

Ultrasound uses sound waves and their echoes to look inside the body, such as the inner parts of the eye. For this test, a small ultrasound probe is placed up against the eyelid or eyeball. The sound wave echoes are converted by a computer into an image on a screen.

Ultrasound is one of the most common imaging tests to confirm a child has retinoblastoma. This test can also be very useful when tumors in the eye are so large they prevent doctors from seeing inside the whole eye.

This test does not hurt and does not expose the child to radiation, but the child may need to be given medicine to help keep them calm or even asleep during the test so the doctor can get a good look at the eye.

OCT is like ultrasound, but it creates detailed images of the back of the eye using light waves instead of sound waves using a handheld tool. It can be used to help diagnose new tumors and watch for recurrent tumors that may be hard to see by visual exam due to scars on the back of the eye after treatment.

An MRI scan makes detailed images of the soft tissues in the body using radio waves and strong magnets (instead of x-rays). MRI scans often are used for retinoblastomas because they provide very detailed images of the eye and surrounding structures, without using radiation. This test is also very good for looking at the brain and spinal cord.

Most children with retinoblastoma will have an MRI scan as part of their initial workup. For children with bilateral retinoblastomas (tumors in both eyes), many doctors continue to do MRI scans of the brain for several years after treatment to look for brain tumors (sometimes called trilateral retinoblastoma).

Young children may need medicine to help keep them calm or even asleep during this test.

CT scans can help determine the size of a retinoblastoma tumor and how much it has spread within the eye and to nearby areas.

Normally, either a CT or an MRI scan is needed, but usually not both. Most doctors prefer to use MRI because CT scans use x-rays, which might raise a child’s risk for other cancers in the future. However, a CT scan can show deposits of calcium in the tumor much better than an MRI, which can be very helpful when the diagnosis of retinoblastoma is not clear.

A bone scan can help show if the retinoblastoma has spread to the skull or other bones. Most children with retinoblastoma do not need to have a bone scan. It is normally used only when there is a strong reason to think retinoblastoma might have spread outside the eye.

For this test, a small amount of low-level radioactive material is injected into the blood and travels to the bones. A special camera can detect the radioactivity and create a picture of the skeleton.

Areas of active bone changes appear as “hot spots” on the scan. These areas may suggest cancer is in an area, but other bone diseases can also cause the same pattern. To help tell these apart, other tests such as plain x-rays or MRI scans of the bone might be needed.

While sampling the tumor is discouraged in retinoblastoma, newer techniques of testing for cell-free DNA in the blood or aqueous humor (liquid in the front part of the eye) are used by some centers. These tests can be used to diagnose and monitor treatment response in retinoblastoma.

These tests are not used in all treatment centers. Talk to your cancer care team about whether a liquid biopsy will be used in the diagnosis and treatment of your child’s tumor.

A bone marrow biopsy and aspiration procedure might be done to see if the cancer has spread to the bone marrow, the soft, inner part of certain bones. These tests are usually not needed unless the retinoblastoma has grown outside the eye and doctors suspect it might have also spread to the bone marrow.

The tests typically are done at the same time. The samples are usually taken from the hip bones, but sometimes they may be taken from other bones. Usually the child is given medicine (anesthesia) so they will be asleep during the procedure.

For a bone marrow aspiration, a thin, hollow needle is inserted into the bone and a syringe is used to suck out a small amount of liquid bone marrow.

For a bone marrow biopsy, a small piece of bone and marrow is removed by placing a slightly larger needle in the bone. Once the biopsy is done, pressure is applied to the site to help stop any bleeding.

The samples are then sent to a lab for tests and looked at under a microscope.