Acute myelocytic leukemia

Definition

Acute myelocytic leukemia (AML) is an acute cancer that affects white blood cells, primarily those of the granulocyte or monocyte types.

Description

Acute myelogenous leukemia and acute nonlymphocytic leukemia (ANLL)are other names for AML and refer to the identical disease.

The cells that make up blood are produced in the bone marrow and the lymph system. The bone marrow is the spongy tissue found in the large bones of the body. The lymph system includes the spleen (an organ in the upper abdomen), the thymus (a small organ beneath the breastbone), and the tonsils (an organ in the throat). In addition, the lymph vessels (tiny tubes that branch like blood vessels into all parts of the body) and lymph nodes (pea-shaped organs that are found along the network of lymph vessels) are also part of the lymph system. The lymph is a milky fluid that contains cells. Clusters of lymph nodes are found in the neck, underarm, pelvis, abdomen, and chest.

The main types of cells found in the blood are the red blood cells (RBCs), which carry oxygen and other materials to all tissues of the body; white blood cells (WBCs), which fight infection; and the platelets, which play a part in the clotting of the blood. The white blood cells can be further subdivided into three main types: granulocytes, monocytes, and lymphocytes.

The granulocytes, as their name suggests, have particles (granules) inside them. These granules contain special proteins (enzymes) and several other substances that can break down chemicals and destroy microorganisms such as bacteria. Monocytes are the second type of white blood cell. They are also important in defending the body against pathogens. The lymphocytes form the third type of white blood cell.

The bone marrow makes stem cells, which are the precursors of the different blood cells. These stem cells mature through stages into either RBCs, WBCs, or platelets. In acute leukemias, the maturation process of the white blood cells is interrupted. The immature cells (or "blasts") proliferate rapidly and begin to accumulate in various organs and tissues, thereby affecting their normal function. This uncontrolled proliferation of the immature cells in the bone marrow affects the production of the normal red blood cells and platelets as well.

Acute leukemias are of two types: acute lymphocytic leukemia and acute myelogenous leukemia. Different types of white blood cells are involved in the two leukemias. In acute lymphocytic leukemia (ALL), it is the lymphocytes that become cancerous. AML is a cancer of the monocytes and/or granulocytes.

The reason certain leukemias are now called acute is because of names received decades ago. Before the discovery of modern methods of cancer treatment, these were illnesses that progressed rapidly. In contrast, chronic leukemias were, in this period before newer methods had been invented, illnesses that progressed more slowly.

Demographics

Approximately 23 new cases of AML appear per each million Americans each year. Men are somewhat more likely to develop AML than are women. Approximately 29 new cases appear per every million males while approximately 19 new cases appear per every million females per year.

Older persons are considerably more likely to develop AML. Approximately 13 people per million younger than 65 years of age will develop AML. In contrast, 122 people per million older than 65 years of age will develop the disease.

AML sometimes affects children. About 500 children develop AML in the United States every year. Approximately one in five of all children who develop leukemia develop AML. The disease affects boys and girls in roughly equal numbers. Children of all ethnic groups may develop the disease. If one of two identical twins develops AML, the chances are considerable that the other twin will develop it as well.

Causes and symptoms

AML is neither contagious nor inherited. However, people who suffer from certain genetic disorders, such as Fanconi anemia, Klinefelter syndrome, Patau syndrome, Bloom syndrome, and Down syndrome, are at greater risk of developing AML than the general population. A child with Down syndrome is roughly 14 times as likely as the average child to develop leukemia.

Any person who has been exposed to radiation at high doses is at heightened risk of developing AML, as are people exposed to benzene, a chemical used in the manufacture of plastics, rubber, medicines, and certain other chemicals. Another group of people at increased risk for developing AML are those who have been treated for cancer with certain medicines, for example, chloramphenicol, phenylbutazone, chloroquine, and methoxypsoralen.

The symptoms of AML are generally vague and non-specific. A patient may experience all or some of the following symptoms:

• weakness or chronic fatigue

• fever of unknown origin

• shortness of breath

• weight loss that is not due to dieting or exercise

• frequent bacterial or viral infections

• headaches

• skin rash

• non-specific bone pain

• easy bruising

• bleeding from gums or nose

• blood in urine or stools

• enlarged lymph nodes and/or spleen

• abdominal fullness

A small minority of patients with AML have a tumor of leukemic cells at diagnosis. Such a tumor may appear in the lung, breast, brain, uterus, ovary, stomach, prostate, or certain other places in the body.

Some children with AML present to their doctor with very few symptoms, while other children present with severe symptoms. Anemia is usually present. The symptoms of the anemia may include fatigue, dizziness, headache, paleness of the skin, or, infrequently, congestive heart failure. Easy bruising, bleeding gums, and nosebleeds may be present, as may fever. There may be swollen gums, bone pain or joint pain, or, rarely, an actual tumor. Some infants with AML have skin disorders.

Diagnosis

Like all cancers, acute leukemias are best treated when found early. There are no screening tests available.

A thorough diagnostic evaluation should be conducted. This is important because the doctor must determine more than whether or not AML is present. If it is suspected, has it affected the general health of the patient? Is the patient capable of undergoing rigorous treatment?

A doctor who suspects leukemia may start by obtaining a thorough medical history. The doctor may then conduct a very thorough physical examination to look for enlarged lymph nodes in the neck, underarm, and pelvic region. Swollen gums, enlarged liver or spleen, bruises, or pinpoint red rashes all over the body are among the signs of the disease. In addition, the physician may examine the teeth and look for dental abscesses, and may explore whether back pain is present.

Urine and blood tests may be ordered to check for microscopic amounts of blood in the urine and to obtain a complete differential blood count. This count will give the numbers and percentages of the different cells found in the blood. An abnormal blood test might suggest leukemia. Patients suffering from AML may have high leukocyte counts and typically have low counts of both red blood cells and platelets. Many patients with AML have low counts of all of the major components of the blood. A microscopic exploration of the blood will usually show that leukemic blast cells are present. However, the diagnosis has to be confirmed by more specific tests.

The doctor may perform a bone marrow aspiration and biopsy to confirm the diagnosis of leukemia. Aspiration involves the withdrawal of a liquid sample of marrow. During the biopsy, a cylindrical piece of bone and marrow is removed. The tissue is generally taken out of the hipbone. These samples are sent to the laboratory for examination. In addition to diagnosis, the aspiration and biopsy may be repeated during the treatment phase of the disease to see if the leukemia is responding to therapy.

A chest x ray is taken. Cardiac tests, including an electrocardiogram, are conducted. The patient is examined for possible infection. These diagnostic procedures often disclose bleeding in the stomach or intestines, and there may be bleeding in the lungs, brain, or eyes. Anemia is often present and may be severe.

Cytogenetic studies, which examine the number and shape of the chromosomes in the DNA of individual blast cells, should be conducted in addition to the immunophenotyping of cells of the bone marrow. This procedure involves applying various stains to the marrow cells. These stains help doctors identify some of the proteins lying on the surface of the cells.

A spinal tap (lumbar puncture) is another procedure the doctor may order to diagnose leukemia. In this procedure, a small needle is inserted into the spinal cavity in the lower back to withdraw some cerebrospinal fluid and to look for leukemic cells.

Standard imaging tests such as x rays may be used to check whether the leukemic cells have invaded other areas of the body, such as the bones, chest, kidneys, abdomen, or brain. Other tests, such as computed tomography scans (CT scans), magnetic resonance imaging (MRI), or gallium scans, are not typical for AML but may also be performed.

Children with AML are given most of the same studies used for adults.

Clinical staging, treatments, and prognosis

Unlike several other cancers, AML is not staged. However, a classification system is used to separate different forms of AML. One of the most important classification systems, devised by a team of physicians, is known as the French-American-British (FAB) Classification System.

The goal of AML treatment is to achieve a complete remission (CR). What is a complete remission? It is a measure that indicates that the patient's disease has gotten markedly better in several ways. In general, it might be said that CR is achieved once the body has regained its ability to produce blood cells normally. At this point, the number of blood cells of various types should return to normal ranges, while none of the immature cells called leukemic blast cells should be present in the blood or the marrow.

Chemotherapy is the use of drugs to kill cancer cells. It is usually the treatment of choice and is used to relieve symptoms and achieve long-term remission of the disease. Generally, combination chemotherapy, in which multiple drugs are used, is more efficient than using a single drug for the treatment. Some drugs may be administered intravenously through a vein in the arm; others may be given by mouth in the form of pills. If the cancer cells have invaded the brain, then chemotherapeutic drugs may be put into the fluid that surrounds the brain and spinal cord. This is known as intrathecal chemotherapy. Chemotherapy should start soon after diagnosis.

Patients who are anemic or who have low platelet counts should receive transfusions. These transfusions should be sufficient to restore counts of various components of the blood to adequate levels.

There are two phases of treatment for leukemia. The first phase is called induction therapy. During this phase, the main aim of treatment is to reduce the number of leukemic cells as much as possible and induce a remission in the patient. A variety of chemotherapy agents may be used during the induction therapy portion of AML treatment. In 2001, the chemotherapy agent Ara-C (cytarabine) is often used in combination with either daunorubicin or idarubicin (Idamycin). Other doctors add etoposide to this combination of chemotherapy agents. For older patients, Ara-C and mitoxantrone may be used. Some patients benefit from receiving high doses of chemotherapy drugs. As of 2001,patients who do not achieve CR, as well as those who achieve CR but then relapse, may be given mitoxantrone plus etoposide.

The second phase of treatment is initiated once CR is achieved. This is called post-remission or consolidation therapy. The goal of therapy now becomes killing any remaining cells and maintaining the remission for as long as possible. There are various ways of attempting to reach this goal. One involves additional chemotherapy. Another involves bone marrow transplantation (BMT), also called stem cell transplant (SCT). Transplantation therapy has been studied very thoroughly. It involves taking blood-making cells, whether from the patient or from another person, and infusing them into the patient following removal of the diseased marrow, with either high doses of chemotherapy or total body irradiation. These procedures are potentially very effective because of the remarkable ability of these cells to create a sustained replacement of the patient's blood cells. Other strategies may also be applied. Approaches used for patients younger than 60 years of age may differ from those used for patients of older ages.

Because leukemia cells can spread to all the organs via the blood stream and the lymph vessels, surgery is not considered an option for treating leukemias.

Children with AML also receive induction therapy. Often two or three medicines are used in conjunction with one another. After remission is achieved in a young patient, postremission therapy is started. The type of postremission therapy depends largely on the type of AML the patient has. It may involve additional chemotherapy or, alternatively, bone marrow transplantation. Chemotherapy to the central nervous system (CNS) is given to most children, since without it, roughly one in five will develop CNS relapse. The CNS includes the brain and spinal cord.

The prognosis of patients with AML varies. A number of different matters should be examined before the prognosis of any individual patient is assessed. The most important of these is whether or not the patient attains a complete remission (CR). The most important consideration in terms of whether a patient is likely to achieve CR is the patient's age. However, it may be that chronological age is not what really matters. Rather, to a large extent, what is truly significant is the patient's ability to survive the difficulties associated with induction therapy. For example, the patient who has some other disease in addition to AML may have a more difficult time with the rigors of the therapy. Yet, it is also true that older patients are more likely to have AML that expresses certain characteristics associated with poorer outcomes.

Other factors also affect the patient's prognosis. For example, in the tests performed during diagnosis, the chromosomes of cells are examined. Some chromosomal findings are associated with a good prognosis. Others are only mildly good, while still others indicate the patient is less likely to achieve CR.

Other factors that may provide physicians with hints as to the patient's prognosis include: how long symptoms were present before the illness was diagnosed, and how quickly immature blast cells disappear after treatment is started.

Coping with cancer treatment

One of the most important aspects of treatment is guaranteeing that the patient will have the supportive care needed to come through the treatment period with physical and emotional strength intact. Part of what this means is that AML should be treated in major cancer centers, because only these centers have the expertise necessary to provide not only the right medicine but also the accompaniments of good treatment.

One way physicians help AML patients cope with treatment is to guarantee that adequate blood bank support is available. Many patients require platelet transfusions.

One of the great dangers to patients during induction treatment and other steps of treatment is the threat of serious infectious disease. These patients have weakened blood components and are therefore more susceptible to infectious illness than the average person is. The leading cause of death for patients receiving induction treatment and chemotherapy following remission is infectious illness.

To help build the patient's white cell count, doctors may prescribe growth factors. These encourage the body to produce certain types of blood cells. The types of growth factors prescribed most frequently are granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF).

The psychological aspects of cancer treatment are a major concern. Patients should ask their physician about local support groups and survivor networks that can help with the stresses associated with this disease.

Prevention

High doses of radiation and exposure to the chemical benzene (used in the manufacture of plastics, rubber, and medicines) are strong risk factors. With the exception of people with such rare genetic conditions as Fanconi anemia, Klinefelter syndrome, Patau syndrome, Bloom syndrome, and Down syndrome, there is no known genetic predisposition to AML.

KEY TERMS

Blasts

An immature cell.

Bone marrow

Spongy tissue found in the large bones of the body.

Cytogenetic testing

Analysis of parts of the nucleus of blast cells.

Granulocytes

White blood cells containing particles or granules.

Immunophenotype

A test that involves placing various sorts of stains on bone marrow cells to help identify the chemicals located on the cell surfaces.

Monocytes

Another type of white blood cell, important in the defense against pathogens.

QUESTIONS TO ASK THE DOCTOR
• What type of AML do I have? What does it mean to have this variant of the disease?

• How can I obtain supportive care so I come through this not only alive but with my family and emotional life intact?

• Do I have any infections?

• What are the results of the cytogenetic testing?

• What are the results of the immunophenotyping?

• What is my prognosis?

• Are blasts present?

• Are blood counts returning to normal levels?

• Has complete remission been achieved?

• What can I do to lower my risk of infection during chemotherapy?