How is retinoblastoma staged?
The stage of cancer is a description of how far the cancer has spread. The outlook (prognosis) for people with cancer depends, to a large extent, on the cancer’s stage. The stage of a cancer is one of the most important factors in choosing treatment.
Retinoblastoma is staged based on the results of eye exams, imaging tests, and any biopsies that were done. These tests were described in the previous section, “How is retinoblastoma diagnosed?”
A staging system is a standard way for your child’s cancer care team to describe how far a cancer has spread. Doctors use staging systems to predict the outlook for saving the child’s vision, as well as for survival and the likelihood that certain treatments will be effective.
Several detailed systems can be used to stage retinoblastoma. But for practical purposes, when determining the best treatment options, doctors often divide retinoblastomas into 2 main groups:
- Intraocular retinoblastoma: The cancer is still within the eye.
- Extraocular retinoblastoma: The cancer has spread beyond the eye. Extraocular cancers can be further divided into orbital retinoblastomas, which have spread only to the eye socket, and metastatic retinoblastomas, which have spread to distant parts of the body, such as the brain or bone marrow.
In the United States, most retinoblastomas are diagnosed before they have spread outside of the eye, so staging systems that apply only to intraocular retinoblastoma are used most often in this country. There are 2 staging systems for intraocular retinoblastomas. It is important to know that regardless of the stage, almost all children with intraocular retinoblastoma can be cured if they are properly treated.
International Classification for Intraocular Retinoblastoma
The International Classification for Intraocular Retinoblastoma is the newer staging system, which takes into account what has been learned about the disease in recent decades. Most doctors now use this system. It divides intraocular retinoblastomas into 5 groups, labeled A through E, based on the chances that the eye can be saved using current treatment options.
Small tumors (3 millimeters [mm] across or less) that are only in the retina and are not near important structures such as the optic disk (where the optic nerve enters the retina) or the foveola (the center of vision).
All other tumors (either larger than 3 mm or small but close to the optic disk or foveola) that are still only in the retina.
Well-defined tumors with small amounts of spread under the retina (subretinal seeding) or into the gelatinous material that fills the eye (vitreous seeding).
Large or poorly defined tumors with widespread vitreous or subretinal seeding. The retina may have become detached from the back of the eye.
The tumor is very large, extends near the front of the eye, is bleeding or causing glaucoma (high pressure inside the eye), or has other features that mean there is almost no chance the eye can be saved.
The Reese-Ellsworth staging system
Some doctors may still use the Reese-Ellsworth staging system to classify retinoblastomas that have not spread beyond the eye. This system can help determine the likelihood of preserving vision while still effectively treating the tumor.
This system was developed in the 1960s, when most children were being treated with external beam radiation therapy (EBRT). Terms such as favorable, doubtful, and unfavorable used in this staging system refer to the likelihood that the cancer could be treated effectively while preserving the affected eye. These terms do not refer to the likelihood of the child’s survival. Indeed, more than 9 in 10 children with intraocular retinoblastomas are cured. The major challenge is saving their sight.
To explain the groupings below, it helps to define a few terms. The optic disk is the end of the optic nerve where it is attached to the retina. Retinoblastomas are diagnosed by looking at the retina through an ophthalmoscope, so doctors cannot measure their size directly using a ruler. Instead they compare the size of the tumor with the size of the optic disk, which is usually about 1.5 millimeters (1/16 inch) across. For example, a tumor estimated to be 3 times the size of the disk (3 disk diameters or 3 DD) would be about 4.5 millimeters (3/16 inch) across.
The equator is an imaginary line that divides the front and back halves of the eyeball.
The Reese-Ellsworth staging system divides intraocular retinoblastoma into 5 groups. The higher the group number, from 1 to 5, the lower the chance of controlling the retinoblastoma or of saving the eye or any useful vision.
Group 1 (very favorable for saving [or preserving] the eye)
- 1A: one tumor, smaller than 4 disc diameters (DD), at or behind the equator
- 1B: multiple tumors smaller than 4 DD, all at or behind the equator
Group 2 (favorable for saving [or preserving] the eye)
- 2A: one tumor, 4 to 10 DD, at or behind the equator
- 2B: multiple tumors, with at least one 4 to 10 DD, and all at or behind the equator
Group 3 (doubtful for saving [or preserving] the eye)
- 3A: any tumor in front of the equator
- 3B: one tumor, larger than 10 DD, behind the equator
Group 4 (unfavorable for saving [or preserving] the eye)
- 4A: multiple tumors, some larger than 10 DD
- 4B: any tumor extending anteriorly (toward the front of the eye) to the ora serrata (front edge of the retina)
Group 5 (very unfavorable for saving [or preserving] the eye)
- 5A: tumors involving more than half of the retina
- 5B: vitreous seeding (spread of tumors into the gelatinous material that fills the eye)
This staging system was first designed to determine how useful radiation therapy might be in a given patient, but it can still provide some useful information about which current treatments might be most effective. For example:
A group 1 retinoblastoma very likely can be controlled with treatments such as chemotherapy, photocoagulation, cryotherapy, thermotherapy, brachytherapy, or external beam radiation therapy while still preserving vision in the eye.
Other staging systems
Other staging systems that include both intraocular retinoblastomas and those that have spread beyond the eye (extraocular retinoblastomas) may be used by some doctors. These may be especially useful in countries where these cancers are more likely to have spread by the time they are found. For example, the American Joint Commission on Cancer (AJCC) has developed a staging system that takes into account 3 key pieces of information:
- T: the size of the main (primary) tumor and how far it has grown within and outside of the eye
- N: whether or not the cancer has reached the lymph nodes (small, bean shaped collections of immune cells, to which cancers sometimes spread)
- M: whether or not the cancer has spread (metastasized) to distant sites, such as the bone marrow, brain, skull, or long bones
This system can be used to describe the extent of retinoblastomas in detail, particularly for those cases when the disease has spread outside of the eye, which rarely happens in the United States.
Be sure to ask your child’s doctor if you have any questions about the stage of your child’s cancer.
Last Medical Review: 12/05/2013
Last Revised: 12/05/2013