Retinoblastoma(Rb) is a cancer of the retina. Retinoblastoma is the most common primary ocular malignancy of childhood. Although this disorder can occur at any age, it usually develops in young children. Most cases of retinoblastoma occur in only one eye, but both eyes can be affected. Untreated, retinoblastoma is almost always fatal, hence the importance of early diagnosis and treatment.
Retinoblastoma can occur in two forms : -
- An inherited form where there are often tumours in both eyes (bilateral) or sometimes only in one eye
- A non-inherited form where there is a tumour in only one eye (unilateral)
Retinoblastoma is related to chromosome 13. Retinoblastoma occurs when a cell of the growing retina develops a mutation in the RB gene (a tumor-suppressor gene). This mutation causes the cell to grow out of control and become cancerous.
Mutations in the RB1 gene are inherited in an autosomal dominant pattern, which means that one copy of the altered gene in each cell is sufficient to increase cancer risk. A person with retinoblastoma may inherit an altered copy of the gene from one parent, or the altered gene may be the result of a new mutation.
The most common way of presentation is a white reflex (leukocoria) behind the pupil. This is sometimes called the cat's eye reflex. A white glow in the eye that is often seen in photographs taken with a flash; instead of the typical "red eye" from the flash, the pupil may appear white or distorted. White spots in the pupil, crossed eyes, A red, painful eye poor vision, the iris may be a different color in each eye.
A few special tests like ultrasonography, CT scan, X-rays, MRI, blood tests, spinal tap, bone marrow biopsy etc. may be done to establish the diagnosis and to find out the extent of the disease.
Treatment options depend upon the size and location of the tumor. Small tumors may be treated by laser surgery. Radiation and chemotherapy may be needed if the tumor has spread beyond the eye. Chemotherapy is the treatment of choice for most unilateral cases.
There are several staging systems for retinoblastoma. For treatment, retinoblastoma is classified as intraocular (within the eye) or extraocular (outside the eye).
The following stages are used for retinoblastoma : -
- Intraocular retinoblastoma : - Cancer is found in the eye but has not spread to tissues around the outside of the eye or to other parts of the body.
- Extraocular retinoblastoma : - The cancer has spread beyond the eye. It may be found in tissues around the eye or it may have spread to the central nervous system (brain and spinal cord) or to other parts of the body such as the bone marrow or lymph nodes.
There are three ways that cancer spreads in the body : -
- Through tissue. Cancer invades the surrounding normal tissue.
- Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
- Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.
When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.
Q. What causes retinoblastoma ?
In children with the genetic, ie the inheritable form of retinoblastoma, we know that there is something wrong with a small piece of the genetic material on chromosome 13, called the RB1 gene. Chromosomes contain the genetic codes which control the way cells grow and develop, and when a portion of the chromosome is missing or one of the genetic codes is altered in some way, which is known as a mutation, a cancer may develop.
In some children with the genetic form of retinoblastoma, the defective RB1 gene is inherited from one of the parents, however, in the majority of cases, the defect in this gene occurs during the early stages of foetal development, some time before the child is born. We do not know what causes the abnormality in the gene to develop. It is most likely to be a random mistake in the copying process which occurs when a cell divides; such a mistake is known as a mutation.
Some people worry this cancer is infectious, there is absolutely no evidence that anybody can "catch" retinoblastoma, and parents should reassure their friends on this account.
Leukocoria (white pupil) and misaligned eyes (strabismus) are the most common signs of retinoblastoma. In other cases, the child may have developed neovascular glaucoma and may be in pain. Longstanding glaucoma can cause enlargement of the eye (buphthalmos). Children with neovascular glaucoma and enlargement of the eye are at greater risk for extraocular spread of their retinoblastoma.
A family history of retinoblastoma can be very important. Retinoblastoma was the first cancer to be directly associated with a genetic abnormality (Deletions or mutation of the q14 band of chromosome 13). Retinoblastoma can occur sporadically (without a family history) or it can be inherited (with a family history).
If a genetic mutation is found there is a 45-50% chance that the parents will have another child with retinoblastoma. If there is no family history and no mutation is found, the risk of having a second child with retinoblastoma is 2-5%. The average age of children first diagnosed with retinoblastoma is 18 months.
More than 75% of children with retinoblastoma are first noted to have a "white-pupil" (which the doctors call leukocoria), or poorly aligned eyes (which the doctors call strabismus), or a red and painful eye (usually due to glaucoma). Other eye diseases which can cause these symptoms include congenital cataract, Toxocara canis, Coat's disease, and persistent hypertrophic primary vitreous (PHPV).
These diseases may look like retinoblastoma, but by performing an examination under anesthesia, specialized blood tests, digital photography, radiographic scans, and ultrasound evaluations ophthalmic oncologists can diagnose intraocular retinoblastoma in over 95% of cases. In order to be 100% correct all the time, eye-cancer specialists would have to perform a biopsy. Biopsies of intraocular retinoblastoma are avoided in order to prevent cancer cells from spreading outside of the eye.
The presence of orbital extension, uveal involvement, and optic nerve invasion are known risk factors for the development of metastatic retinoblastoma.
Retinoblastoma treatment typically requires the cooperation of an ophthalmic oncologist, pediatric oncologist, and radiation therapist. Over the last 30 years, treatment has evolved from simple enucleation (removal of the eye), to eye-sparing radiotherapy, and more recently to chemotherapy-based multi-modality therapy (for selected cases).
Though retinoblastoma has been cured by external beam irradiation, investigators have suggested that radiation may cause an increase in the risk of developing second cancers later in life.
Protocols are currently being evaluated to use chemotherapy to shrink the retinoblastoma in order to treat them with laser therapy, freezing therapy (cryotherapy), and local "plaque" radiation. Where applicable, these techniques are thought to be safer than external beam irradiation for retinoblastoma. There is little long-term data on the safety of this type of multi-modality chemotherapy.
Treatment of retinoblastoma often requires a team of doctors made up of ophthalmic, radiation and pediatric oncologists. These doctors should evaluate your child, discuss all the different forms of treatment, and make them available.
After retinoblastoma diagnosis
After retinoblastoma has been diagnosed, tests are done to find out if cancer cells have spread within the eye or to other parts of the body.
The process used to find out if cancer has spread within the eye or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests and procedures may be used in the staging process:
Eye exam with dilated pupil: An exam of the eye in which the pupil is dilated (opened wider) with medicated eyedrops to allow the doctor to look through the lens and pupil to the retina. The inside of the eye, including the retina and the optic nerve, is examined using a light. Depending on the age of the child, this exam may be done under anesthesia.
Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.
CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the eye, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the eye. This procedure is also called nuclear magnetic resonance imaging (NMRI).
Lumbar puncture: A procedure used to collect cerebrospinal fluid from the spinal column. This is done by placing a needle into the spinal column. This procedure is also called an LP or spinal tap. A lumbar puncture may be done if tests show that the cancer may have spread out of the eye.
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