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While some people with chronic leukemia have one or more known risk factors, most do not. The cause of their cancer remains unknown at this time. Even when a patient has one or more risk factors, there is no way to tell whether it actually caused the cancer. And, many people with one or more cancer risk factors never develop this disease.
Most of the information responsible for development of normal human cells is contained in the chromosomes. Chromosomes are made of DNA. DNA is the chemical that carries the instructions for nearly everything our cells do. During the past few years, scientists have made great progress in understanding how certain changes in DNA can cause normal bone marrow cells to become leukemic cells. We usually resemble our parents because they are the source of our DNA. However, DNA affects more than our outward appearance.
Some genes (packets of our DNA) contain instructions for controlling when our cells grow and divide. Certain genes that promote cell division are called oncogenes. Others that slow down cell division or cause cells to die at the appropriate time are called tumor suppressor genes. We know that cancers can be caused by DNA mutations (gene defects) that turn on oncogenes or turn off tumor suppressor genes.
Sometimes DNA abnormalities a person inherits from a parent greatly increase their risk of developing certain types of cancer. These inherited mutations are very rarely the cause of chronic leukemias.
DNA mutations related to chronic leukemia usually occur during life rather than having been inherited before birth. Acquired mutations may result from exposure to radiation or cancer-causing chemicals such as those in tobacco smoke. Sometimes they occur for no apparent reason. Every time a cell prepares to divide into two new cells, it must duplicate its DNA. This process is not perfect and copying errors can occur. Fortunately, cells have repair enzymes that proofread DNA. But some errors may slip past, especially if the cells are growing rapidly.
Translocations are another type of DNA abnormality involved in developing leukemia. Human DNA is packaged in 23 pairs of chromosomes. A translocation means that some of the DNA from one chromosome becomes attached to a different chromosome. Like mutations, translocations can turn on oncogenes or turn off tumor suppressor genes. Translocations that develop during life are quite common in chronic leukemias. Different types of leukemia typically have translocations that affect different chromosomes. Tests to detect these translocations are sometimes very useful in diagnosing leukemia, predicting prognosis of leukemia patients, and detecting whether the leukemia has come back after treatment.
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