Information about the prevention of cancer and the science of screening appropriate individuals at high-risk of developing cancer is gaining interest. Physicians and individuals alike recognize that the best “treatment” of cancer is preventing its occurrence in the first place or detecting it early when it may be most treatable.
Chronic myeloid leukemia (CML) is the abnormal growth of relatively mature myeloid (white blood) cells. The disease is associated with a chromosomal abnormality, where genetic material from chromosome 9 is transferred to chromosome 22. This forms what is called the Philadelphia chromosome, which plays a role in the development of the disease. This translocation results in the fusion of two proteins, BCR and ABL, which confers a selective advantage to the growth of CML cells over normal cells. The cause of this translocation is unknown.
The average age at diagnosis of CML is 67 years. Initially, there is a gradual increase in mature myeloid cells in the bone marrow. These cells eventually spill into the blood and other organs causing symptoms such as fatigue resulting from anemia and an enlarged spleen. The increase in leukemic cell numbers occurs slowly at first and is referred to as the chronic phase, but cell numbers will invariably begin to increase more rapidly and/or include less mature cells, resulting in the accelerated or blastic phase.
At this time, researchers do not know what causes CML and are trying to solve this problem. Scientists know that CML occurs in males more often than in females and in Caucasians more often than in African-Americans. However, they cannot explain why one person gets CML and another does not. Because the average age at diagnosis is over 67 years, it is suspected that unknown environmental exposure over a long period of time is required to cause CML. By learning what causes this disease, researchers hope to better understand how to prevent and treat it.
The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait, while a non-genetic factor is a variable in a person’s environment, which can often be changed. Non-genetic factors may include diet, exercise, or exposure to other substances present in our surroundings. These non-genetic factors are often referred to as environmental factors. Some non-genetic factors play a role in facilitating the process of healthy cells turning cancerous (i.e. the correlation between smoking and lung cancer) while other cancers have no known environmental correlation but are known to have a genetic predisposition, meaning a person may be at higher risk for a certain cancer if a family member has that type of cancer.
Heredity or Genetic Factors
There are no clear hereditary factors associated with CML. Identical twins of patients with CML are at no greater risk of developing CML than other siblings. This strongly suggests that environmental factors are much more important than genetic factors in the development of CML. It is a scientific mystery as to why only one of a pair of identical twins will develop CML, since the genetics are identical and environmental exposures are similar, if not the same.
HLA is the histocompatibility system that is used to match people for bone marrow, liver and kidney transplants. One study has found that a specific HLA type, DR4, is associated with a lower incidence of CML, however researchers have not yet identified the reason for this decrease.
Environmental or Non-Genetic Factors
The fact that only one of a pair of identical twins usually develops CML suggests that finding the specific cause for leukemia will be difficult if not impossible. However, by studying large numbers of people all over the world, researchers have found certain factors that increase a person’s risk of developing CML.
Exposure to large amounts of high-energy radiation increases the risk of CML. Such radiation was produced by the atomic bomb explosions in Japan during World War II.
Therapy Related Chronic Myeloid Leukemia: Some of the drugs and radiation used to treat other types of cancer may increase an individual’s risk of CML. Low-dose radiation used in the past to treat a variety of non-malignant conditions has been associated with an increased incidence of leukemia, of which 20-30% were CML. Various chemotherapy and immunosuppressive drugs have been associated with an increase in CML. Radioactive iodine treatment of thyroid cancer is also associated with an increased incidence of CML. CML has also been reported after heart transplants where radiation therapy was given.
Viruses and Chronic Myeloid Leukemia: Scientists have identified a virus that seems to increase the risk for one very uncommon type of leukemia. However, this virus has no known association with common forms of leukemia including CML. Scientists throughout the world continue to study viruses and other possible risk factors for leukemia.
Prevention of Chronic Myeloid Leukemia
Cancer is largely a preventable illness. Two-thirds of cancer deaths in the U.S. can be linked to tobacco use, poor diet, obesity, and lack of exercise. All of these factors can be modified. Nevertheless, an awareness of the opportunity to prevent cancer through changes in lifestyle is still under-appreciated. The overwhelming majority of cases of CML cannot be prevented since we do not know the cause of this disease.
Diet: Diet is a fertile area for immediate individual and societal intervention to decrease the risk of developing certain cancers. Numerous studies have provided a wealth of often-contradictory information about the detrimental and protective factors of different foods.
There is convincing evidence that excess body fat substantially increases the risk for many types of cancer. While much of the cancer-related nutrition information cautions against a high-fat diet, the real culprit may be an excess of calories. Studies indicate that there is little, if any, relationship between body fat and fat composition of the diet. These studies show that excessive caloric intake from both fats and carbohydrates lead to the same result of excess body fat. The ideal way to avoid excess body fat is to limit caloric intake and/or balance caloric intake with ample exercise.
It is still important, however, to limit fat intake, as evidence still supports a relationship between cancer and polyunsaturated, saturated and animal fats. Specifically, studies show that high consumption of red meat and dairy products can increase the risk of certain cancers. One strategy for positive dietary change is to replace red meat with chicken, fish, nuts and legumes.
High fruit and vegetable consumption has been associated with a reduced risk for developing at least 10 different cancers. This may be a result of potentially protective factors such as carotenoids, folic acid, vitamin C, flavonoids, phytoestrogens and isothiocyanates. These are often referred to as antioxidants.
There is strong evidence that moderate to high alcohol consumption also increases the risk of certain cancers. One reason for this relationship may be that alcohol interferes with the availability of folic acid. Alcohol in combination with tobacco creates an even greater risk of certain types of cancer.
Exercise: Higher levels of physical activity may reduce the incidence of some cancers. According to researchers at Harvard, if the entire population increased their level of physical activity by 30 minutes of brisk walking per day (or the equivalent energy expenditure in other activities), we would observe a 15% reduction in the incidence of colon cancer.
Screening and Early Detection of Chronic Myeloid Leukemia
For many types of cancer, progress in the areas of cancer screening and treatment has offered promise for earlier detection and higher cure rates. The term screening refers to the regular use of certain examinations or tests in persons who do not have any symptoms of a cancer but are at high risk for that cancer. When individuals are at high risk for a type of cancer, this means that they have certain characteristics or exposures, called risk factors that make them more likely to develop that type of cancer than those who do not have these risk factors. The risk factors are different for different types of cancer. An awareness of these risk factors is important because 1) some risk factors can be changed (such as smoking or dietary intake), thus decreasing the risk for developing the associated cancer; and 2) persons who are at high risk for developing a cancer can often undergo regular screening measures that are recommended for that cancer type. Researchers continue to study which characteristics or exposures are associated with an increased risk for various cancers, allowing for the use of more effective prevention, early detection, and treatment strategies.
Approximately 20% of CML cases are diagnosed during routine examinations or examinations for other illnesses. The most common symptoms are fatigue and weight loss associated with a high white blood cell count, large spleen and low red blood cell levels. Another common occurrence is bleeding which is unrelated to low or high platelet counts in the blood, but is related to the fact that the platelets don’t work well. Young male patients tend to present with more advanced symptoms than older individuals.
In order for screening to be effective, patients at risk need to be identifiable and this is currently impossible. The average age for developing CML is over 67 years. People over the age of 65 should probably have a physical examination and routine screening every 6 months. Screening is best done by a careful physical examination and determination of blood counts. A bone marrow examination is not necessary unless the blood counts are abnormal or there is some definable abnormality upon physical examination.