Retinoblastoma is a form a cancer that afflicts the retina, the region at the back of the eye that senses light. Most cases of retinoblastoma occur in young children; up to 95 percent of all cases are diagnosed in children 5 years old or younger, according to the National Cancer Institute. Left untreated, retinoblastomas are often fatal; however, the condition can be managed and treated if diagnosed early. Many times, the exact cause of retinoblastomas is unclear.
Cancer Causes
The cells in the body are constantly growing and dying as new cells arise to replace old cells. Sometimes, the old cells do not die when they should, or new cells start growing faster than they should, which causes a tumor, a mass of cells growing out of control. Certain genes, called tumor suppressor genes, have the job of slowing down the growth of cells or telling old cells to die. Other genes, known as oncogenes, are responsible for telling cells to grow faster. Many types of cancer, like retinoblastoma, arise when either oncogenes or tumor suppressors become mutated, or damaged.
Inherited Causes
Roughly a third of all children who develop retinoblastoma inherit a mutated form of a tumor suppressor gene called RB1 from their parents, explains the American Cancer Society. Healthy cells have two copies of the RB1 tumor suppressor that make sure the old cells in the eye die when they should. Retinoblastoma only occurs when both copies of the RB1 gene become mutated. Children who inherit one mutated copy only need to develop one more mutation in the other RB1 gene in order to develop retinoblastoma. Almost 90 percent of children who inherit one mutated copy of RB1 will develop a mutation in the other RB1 gene and develop retinoblastoma.
Sporadic Causes
Retinoblastoma can develop even if a mutation is not inherited. In about two-thirds of retinoblastoma cases, the mutations that cause the disease develop spontaneously. As of 2010, doctors do not definitively know what causes the sporadic mutations that cause cancer. The DNA that makes up genes in the body can be slightly unstable, spontaneously developing mutations as new cells are made. Some environmental factors, such as radiation from the sun or harsh chemicals, can increases the chance of mutations occurring, explains the textbook "Molecular Cell Biology." Due to chance or environmental factors, retinoblastoma develops when both copies of the RB1 tumor suppressor gene mutate.
