Cancer is a process of uncontrolled abnormal cell growth and development. Under normal circumstances, cells are formed, mature, carry out their intended function, and then die. New cells are constantly regenerated in the body to replace those cells and to maintain normal cellular function.
Cancer represents the disturbance of this process, which can occur in several ways.
Cells may grow and reproduce in a disorganized and out-of-control fashion. Cells may fail to develop properly, so they will not function normally. Cells may fail to die normally. One or a combination of these processes may occur when cells become cancerous.
Leukemia is a cancer of blood-forming cells in the bone marrow. These deranged, immature cells accumulate in the blood and within organs of the body. They are not able to carry out the normal functions of blood cells.
Normal blood contains 3 major groups of cells: white blood cells, red blood cells, and platelets. All 3 types of blood cells develop from one immature cell type, called blood/marrow stem cells, in a process called hematopoiesis.
• These stem cells divide and develop to a more developed, but still immature precursor, called a blast, which then develops through several more stages, into a mature blood cell.
• This process takes place in the bone marrow, which is the soft spongy material found in the center of most bones.
Each type of blood cells has its own different and essential function in the body.
• White blood cells (leukocytes) are part of the immune system and help fight a variety of infections. They also help in the healing of wounds, cuts, and sores.
• Red blood cells (erythrocytes) contain hemoglobin, which carries oxygen to, and removes carbon dioxide from, the cells throughout the various organs of the body.
• Platelets, along with certain plasma proteins, help plug the holes in blood vessels and form clots once blood vessels are damaged or cut.
The first step in the process of stem cell maturation is differentiation into 2 groups: the myeloid stem cell line and the lymphoid stem cell line.
• The myeloid stem cells, or lineage, develop into red blood cells, platelets, and certain types of white blood cells (granulocytes or monocytes).
• The lymphoid stem cells, or lineage, develop into another type of white blood cell (lymphocytes).
• Either lineage can be affected by leukemia. Leukemias that affect the myeloid lineage are called myelocytic (also myelogenous, myeloblastic, or nonlymphocytic) leukemias. Leukemias that affect the lymphoid lineage are called lymphocytic (also lymphoblastic or lymphogenous) leukemias.
Each of the 2 major types of leukemia, myelogenous and lymphocytic, include both acute and chronic forms.
• Acute essentially refers to a disorder of rapid onset. In the acute myelocytic leukemias, the abnormal cells grow rapidly and do not mature. Most of these immature cells tend to die rapidly. In the acute lymphocytic leukemias, growth is not as rapid as that of the myelocytic cells. Rather, the cells tend to accumulate. Common to both types of leukemia is their inability to carry out the functions of healthy white blood cells. Untreated, death occurs within weeks or a few months.
• In the chronic leukemias, the onset tends to be slow, and the cells generally mature abnormally and often accumulate in various organs, often over long intervals. Their ability to fight infections and assist in repairing injured tissues is impaired. However, unlike the acute forms of leukemia, untreated, these disorders may persist for many months or, as in the chronic lymphocytic group, many years. A distinctive feature of the chronic myelocytic type is its invariable conversion, if untreated, to a more rapidly fulminating acute type, leading to rapid death.
In summary, the 4 main types of leukemia are as follows:
• Acute lymphocytic leukemia
• Chronic lymphocytic leukemia
• Acute myelocytic leukemia
• Chronic myelocytic leukemia
Less common types include hairy cell leukemia and human T-cell leukemia.
Leukemia affects people of all ages. Approximately 85% of leukemias in children are of the acute type.
• Acute lymphocytic leukemia (ALL) affects both children and adults but is more common in children. It accounts for 65% of the acute leukemias in children.
• Chronic lymphocytic leukemia (CLL) is essentially an adult disorder and is almost twice as common as chronic myelocytic leukemia.
• Acute myelocytic leukemia (AML) is the most common acute leukemia in adults.
• Chronic myelocytic leukemia (CML) is far more common in adults than in children.
As leukemic cells grow and eventually outnumber normal cells, the following events occur:
• The normal blood cells are disabled, resulting in conditions such as frequent infections, bleeding problems (poor healing of small cuts or sores), and anemia (low red blood cell count).
• The leukemia cells may collect in certain parts of the body, causing pain, swelling, and other problems.
• Identifying the type of leukemia is important, since this determines which treatment is given.
Leukemia is newly diagnosed in about 29,000 adults and 2000 children each year in the United States.
• In adults, the acute leukemias occur in those of all ages, whereas the chronic varieties, particularly CLL, tend to occur in people older than 40 years.
• Leukemia is one of the most common cancers of children.
• Leukemia is more common in people of European descent than in African Americans, Hispanic Americans, Asian Americans, or Native Americans.
Survival rates in leukemia have risen dramatically in the last 40 years with improvements in diagnosis and treatment.
• In 1960, the overall 5-year survival rate for all leukemias was about 14%. It is now about 50%.
• The highest survival rates occur in children with the so-called "common" ALL type.
CAUSES OF LEUKEMIAS
The exact cause of leukemia is unknown.
• As with other cancers, smoking is considered a risk factor for leukemia, but many people who develop leukemia have never smoked, and many people who smoke never develop leukemia.
• Long-term exposure to chemicals such as benzene or formaldehyde, typically in the workplace, is considered a risk factor for leukemia, but this accounts for relatively few cases of the disease.
• Prolonged exposure to radiation is a risk factor, although this accounts for relatively few cases of leukemia. Doses of radiation used for diagnostic imaging such as x-rays and CT scans are nowhere near as prolonged or high as the doses needed to cause leukemia.
Other risk factors for leukemia include the following:
• Previous chemotherapy: Chemotherapy, particularly certain of the alkylating agents and topoisomerase inhibitors, used to treat certain types of cancers, are linked to development of leukemia later. It is likely that radiation treatment adds to the risk of leukemia associated with certain chemotherapy drugs.
• Human T-cell leukemia virus 1 (HTLV-1): Infection with this virus is linked to human T-cell leukemia.
• Myelodysplastic syndromes: In this unusual group of blood disorders, the net outcome is invariably an acute myelocytic process.
• Down syndrome and other genetic diseases: Some diseases caused by abnormal chromosomes may increase risk for leukemia.
• Family history: Having a first-degree relative (parent, brother, sister, or child) who has chronic lymphocytic leukemia increases one’s risk of having the disease by as much as 4 times that of someone who does not have an affected relative.
SIGNS AND SYMPTOMS
Symptoms usually develop fairly quickly in acute leukemias. Most cases of acute leukemia are diagnosed when the person visits his or her healthcare provider after becoming ill. Symptoms develop gradually in chronic leukemias and are generally not as severe as in acute leukemias. About 20% of people with chronic leukemia do not have symptoms at the time their disease is diagnosed.
Some symptoms of leukemia are due to deficiencies of normal blood cells. Others are due to collections of leukemia cells in tissues and organs. Leukemia cells can collect in many different parts of the body, such as the testicles, brain, lymph nodes, liver, spleen, digestive tract, kidneys, lungs, eyes, and skin — in effect, virtually every tissue site.
The following symptoms of leukemia are common to all types:
• Unexplained fevers
• Frequent infections
• Night sweats
• Fatigue (feeling tired or washed out)
• Weight loss
• Easy bleeding or bruising
Collection of leukemia cells in certain parts of the body may cause the following symptoms:
• Headache
• Confusion
• Balance problems
• Blurred vision
• Painful swellings in the neck, under the arms, or in the groin
• Shortness of breath
• Nausea or vomiting
• Abdominal pain and/or swelling
• Testicular pain and/or swelling
• Pain in the bones or joints
• Weakness or loss of muscle control
• Seizures
It is important to emphasize that the symptoms of leukemia are nonspecific. This means that they are not unique to leukemia but are common to a number of diseases and conditions. Only a medical professional is able to distinguish leukemia from the other conditions that cause similar symptoms.
TREATMENT
Specialists who treat blood disorders and other kinds of cancer are either hematologists or hematologist-oncologists. These specialists treat leukemia.
• Children are usually treated by a specialist in childhood cancers (pediatric hematologist or hematologist-oncologist).
• These specialists are usually identified by the primary care physician, or less often, by a friend or relative.
• On other occasions, more than one opinion may be sought by the patient or by the referring primary care physician whenever there is doubt or uncertainty, or whenever personalities are at odds.
• Leukemia patients often find it helpful to take a family member or close friend along to these consultations in order to take notes and assist in remembering some of the points of the discussion. For children with leukemia, such is always the case.
• Most patients are treated in major medical centers with state-of-the-art cancer treatment programs.
Once the patient has had the first encounter with the specialist, he or she will have ample opportunity to ask questions and discuss treatment options. The advantages and disadvantages of various treatment options are thoroughly discussed.
• Leukemia treatment depends almost exclusively on the type. Modifying factors may be age, overall health, and prior therapy. Treatment is almost always carried out as part of carefully controlled multi-center programs so that information from many different areas may be constantly analyzed and altered if the results appear to necessitate changes. The patient is always kept abreast of ongoing treatment activities and changes in the treatment plan.
• Treatment commences only if the patient or the patient's guardian concurs.
• In addition to the blood specialist, the patient's medical care team usually includes a specialist nurse or physician assistant, social worker (and for children, child-life worker), and sometimes a member of the clergy, all of whom play major roles in furthering well being.
PREVENTION
No known way exists to prevent leukemia. Avoiding risk factors such as smoking, exposure to toxic chemicals, and exposure to radiation may help prevent some cases of leukemia.
