Overview
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.
At this time, we do not know what causes acute myeloid leukemia (AML) in the majority of cases. Researchers are trying to solve this problem. Scientists know that AML occurs in males more often than in females and in Caucasians more frequently than in African-Americans. However, they cannot explain why one person gets AML and another does not. 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
Familial AML is a rare type of inherited leukemia which is transmitted by a non-sex chromosome in a dominant fashion. Certain genetic conditions can increase the risk for AML. It is very likely that identical twins who develop AML in the first year of life will both develop the disease. However, after the first year of life, the identical twin of a patient with AML only has a slightly increased risk of developing AML when compared to the general population. This is also true for other siblings. This strongly suggests that environmental factors are much more important than genetic factors for the development of AML. It is a scientific mystery as to why only one identical twin will develop leukemia since the genetics are identical and environmental exposures are similar, if not the same.
One congenital condition, Down syndrome, is associated with an increased likelihood of acute lymphoid and acute myeloid leukemia. Congenital neutropenia (low count of germ-fighting white blood cells) is also associated with an increased incidence of myelodysplastic syndrome and AML. Fanconi’s anemia is a congenital or inherited bone marrow disorder which often progresses to AML.
Environmental or Non-Genetic Factors
The fact that only one of a pair of identical twins usually gets AML suggests that environmental factors may play the most important role in the development of AML and finding the specific causes 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 AML.
Exposure to large amounts of high-energy radiation increases the risk of leukemia. Such radiation was produced by the atomic bomb explosions in Japan during World War II. Patients with any condition who have received radiation therapy are probably at an increased risk of developing AML. For example, persons with ankylosing spondylitis whose treatment included radiation are at increased risk of developing AML.
Some, but not all, studies show that commercial jet cockpit crews who have flown more than 5,000 hours appear to have an increased incidence of AML. Jet cockpit crews do have an increased incidence of melanoma and skin cancer which may or may not be due to more ultraviolet and more gamma radiation exposure at high altitudes.
Some early research suggested that exposure to electromagnetic fields was a possible risk factor for leukemia. (Electromagnetic fields are a type of low-energy radiation that comes from power lines and electric appliances.) However, more recent studies have failed to document an increased incidence of AML in individuals living near power lines.
Workers exposed to certain chemicals, such as benzene, over a long period of time are at a higher risk for AML. Specific chromosomal aberrations, including the 8:21 translocation associated with AML, have been detected in the white blood cells of benzene workers before the detection of leukemia. Workers in the petroleum industry prior to 1960 appeared to have an increased incidence of AML, but more recent studies have not shown this. This change may represent better and safer working conditions. The incidence of AML is increased in areas of high automobile density, possibly as a result of exposure to benzene from gasoline. This observation is further supported by the fact that no other cancer or leukemia is increased in areas of high automobile density.
Therapy Related Acute Myeloid Leukemia: Some of the drugs used to treat other types of cancer may increase a person’s risk of AML. There is an increased incidence of myelodysplastic syndromes and AML in patients who receive conventional doses of chemotherapy, as well as in patients receiving high-dose chemotherapy with autologous or allogeneic stem cell infusion. Approximately 4% of children treated for Hodgkin’s disease will develop a second cancer, with the most common being AML. Treatment of cancer with the chemotherapy drug, etoposide, is associated with the highest incidence of AML. A 5% incidence of myelodysplasia or AML has been observed in patients receiving mitoxantrone as adjuvant therapy for breast cancer which is higher than observed with other chemotherapy drugs used for adjuvant therapy. Radiation combined with chemotherapy significantly increases the risk of developing myelodysplasia and AML compared to either treatment alone.
Viruses and Acute 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 AML. Scientists throughout the world continue to study viruses and other possible risk factors for leukemia.
Prevention of Acute 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 majority of cases of AML cannot be prevented since we do not know the cause. The few cases associated with benzene exposure are preventable with better workplace conditions. The exact number of cases of AML that could be prevented by avoiding exposure to automobiles is unknown, but this is impractical for the majority of people.
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 Diagnosis
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.
Acute myeloid leukemia is usually diagnosed because patients have signs and symptoms of leukemia including fatigue, weight loss, bleeding, easy bruising or unexplained infections. Occasionally the diagnosis is made on routine physical examination or by performing a white blood count, platelet count and red blood cell determination.
In order for screening to be effective, patients at risk need to be identifiable. With the exception of identifying a few genetic diseases, it is currently impossible to screen for AML. At this point, there is no evidence that early diagnosis of AML improves survival rates in comparison with those of later, symptomatic detection.
Workers in the chemical or petroleum industry need regular screening. Screening consists of a routine blood count, which is part of an annual physical examination. It is important to realize that the average age for developing AML is over 65 years. People over the age of 65 should probably have a physical examination with routine blood counts every 6 months. A bone marrow examination is not necessary unless the blood counts are abnormal or there is some definable abnormality suggestive of AML upon physical examination.