Do We Know What Causes Childhood Leukemia?
The exact cause of most cases of leukemia is not known. However, doctors have found that this cancer is associated with a number of other conditions, which are described in the section on risk factors. It is important to remember that most children with leukemia do not have any known risk factors, and the cause of their cancer is not known at this time.
During the past few years, doctors have made great progress in understanding how certain changes in DNA can cause bone marrow stem cells to develop into leukemia. DNA is the chemical in each cell in our bodies that carries the instructions for nearly everything our cells do. We usually resemble our parents because they are the source of our DNA.
However, DNA affects more than our outward appearance. Some genes (parts of our DNA) contain instructions for controlling when our cells grow and divide. Certain genes that promote cell division are called . Other genes that slow down cell division or cause cells to die at the appropriate time are called . It is known that leukemia can be caused by DNA mutations (defects) that turn on oncogenes or turn off tumor suppressor genes.
Some people with certain types of cancer have DNA mutations they inherited from a parent. These changes increased their risk for the disease. However, although certain inherited diseases can increase a person's risk of developing leukemia, most cases of leukemia are not caused by inherited mutations.
A condition called Li-Fraumeni syndrome, resulting from inherited mutations of the tumor suppressor gene, increases a person's risk of developing leukemia, as well as bone and soft tissue sarcomas, breast cancer, and brain tumors.
Usually, DNA mutations related to leukemia develop after conception rather than having been inherited. Recently, it has been shown that some of these acquired mutations are present at birth, and are presumed to have occurred inside the mother's womb.
Acquired mutations may result from exposure to radiation or cancer-causing chemicals, but usually they occur for no apparent reason. Every time a cell prepares to divide into 2 new cells, it must duplicate its DNA. This process is not perfect, and copying errors occur sometimes. Fortunately, cells have repair enzymes that "proofread DNA, but some errors may slip past, especially when the cells are growing rapidly.
are another type of DNA abnormality that can lead to leukemia. Human DNA is packaged in 23 pairs of chromosomes. A translocation means that a piece of DNA from one chromosome is switched or exchanged with a different chromosome. Translocations can cause oncogenes to be activated or tumor suppressor genes to be turned off. Doctors have found that some of these translocations can be found in blood cells at birth. Most children who have these translocations do not develop leukemia, but some do.
Most leukemias likely come about because of genetic changes that are acquired. Some of these can occur in developing fetuses and are already present at birth. The cause of these is not known.
Although many adult cancers can be prevented by lifestyle changes that reduce certain risk factors, there is currently no known way to prevent most childhood cancers. In addition, most adults and children with leukemia have no known risk factors and, at the present time, there is no way to prevent their leukemias from developing.
Children with a known increased risk of developing leukemia (because of Li-Fraumeni syndrome or Down syndrome, for example) should receive careful, periodic medical checkups. The frequency of leukemia in children with these syndromes, although greater than in the general population, is still very rare.
Treating cancers with radiation and chemotherapy and the use of immune
system-suppressing drugs to avoid rejection of transplanted organs also causes some leukemias. Doctors are currently studying ways to treat patients with cancer and organ transplants that minimize the risk of leukemia. However, the obvious benefits of treating life-threatening diseases with chemotherapy, radiation therapy, or organ transplantation must be balanced against the small chance of developing leukemia several years later.
There are no special tests that can detect leukemia early. The best strategy for early diagnosis is prompt attention to the signs and symptoms of this disease (see "How Is Childhood Leukemia Diagnosed?"). Close observation is important for children with a known genetic abnormality that might increase their risk of leukemia, children who have had another cancer treated with chemotherapy or combined chemotherapy and radiation therapy, and children who have received organ transplants and are taking immune system-suppressing drugs.
