Overview
Leukaemia is a cancer of the white blood cells (WBCs) originating in the bone marrow. Over 7000 people are diagnosed with leukaemia annually in the UK, making it the 10th most common cancer in men and 9th in women. While exposure to radiation, benzene, and some anticancer drugs have been shown to increase the risk of developing leukaemia, and a few cases are associated with genetic disorders or rare viral infections, the cause of most leukaemias is not known.
What is it?
Leukaemia is a bone marrow disorder that arises when one abnormal white blood cell begins to continuously replicate itself. Except in the case of chronic myeloid leukaemia (CML), leukaemic cells do not function normally, i.e. they do not fight infection as they should and they do not die at the same rate as other WBCs. As they accumulate, the cells inhibit the production of the other normal blood cells in the marrow, leading to anaemia, bleeding, and recurrent infections. Over time, the leukaemic cells spread through the bloodstream where they continue to divide, sometimes forming tumours and damaging organs such as the kidney and liver. Since the spleen is responsible for filtering the blood and destroying old cells, it may become enlarged and swollen with the abnormal cells, as can the liver and lymph nodes. If the cells reach the central nervous system and build up in the cerebrospinal fluid that surrounds the brain and spinal column, they can cause headaches and seizures.
The bone marrow, located in the soft centre of the body's larger bones, produces precursors (immature versions) of red blood cells, platelets, and various kinds of white blood cells. The most immature recognisable precursor is called a blast cell. Most of these blood cells mature in the bone marrow before being released into the bloodstream. The WBCs created are grouped into two main categories: lymphoid and myeloid. Myeloid cells (which include neutrophils, basophils, eosinophils, (collectively known as granulocytes due to granules visible inside them) and monocytes) circulate in the blood, killing and digesting bacteria. Lymphocytes, which are found in both the blood stream and the lymphatic system, coordinate the immune response and produce antibodies. Leukaemia arises from any one of these white blood cells. It is categorised both by the type of WBC involved and by how quickly it progresses. Although expanded classifications of the disease exist, the main types of leukaemia can be grouped as:
- Acute lymphocytic leukaemia (ALL). Affects approximately 200 adults each year in the UK. This is a rapidly developing disease that is characterized by large numbers of immature lymphocytes (lymphoblasts). It is the most common type of leukaemia found in children, although it affects both children and adults (usually adults age 65 and older).
- Chronic lymphocytic leukaemia (CLL). This disease progresses more slowly and is characterized by an excess of mature lymphocytes. It tends to be found in those over the age of 55 or 60 and is almost never found in those under 40
- Acute myeloid leukaemia (AML). Affecting people of all ages, although it becomes increasingly common with age and is predominantly found in those over 60, this disease is characterized by production of large numbers of immature granulocyte myeloid cells (myeloblasts) that replace other normal cells in the marrow.
- Chronic myeloid (or granulocytic) leukaemia (CML or CGL). Chronic myeloid leukaemia affects approximately 700 people (mostly adults) in the UK each year. It is an acquired condition that begins in an immature stem cell in the bone marrow when pieces from two chromosomes (9 and 22) break off and switch places (translocation). This results in an altered, fused gene (bcr-abl) on chromosome 22 that produces an abnormal which affects cell growth regulation. This leads to an overproduction of myeloid white blood cells, and the presence of both mature and immature cells in the bloodstream.
Acute leukaemia is often diagnosed because the patient feels ill. They may have symptoms related to not having enough normal cells, such as:
- Weakness, shortness of breath and anaemia due to a lack of red blood cells (which carry oxygen to the body's tissues)
- Bleeding and bruising due to a lack of platelets (which are cell fragments that the body uses in the clotting process to plug holes in leaking blood vessels)
- Recurrent infections due to a lack of normal infection fighting WBCs.
Those with acute leukaemia may also have signs and symptoms related to accumulations of immature white blood cells, such as: bone and joint pain; enlarged lymph nodes, spleen, liver, kidneys, and testicles; and headaches, vomiting, confusion, and seizures (when excess cells collect in the brain or central nervous system). They may also experience fever, weight loss, and night sweats.
Chronic leukaemias often progress slowly and may be found by the doctor during a routine check-up before any symptoms are noticed, or they may cause milder forms of the same symptoms noticed with acute leukaemia. The rate at which they progress depends on the patient. CLL may be monitored for decades and never require treatment, but usually progresses slowly to cause symptoms and may do quickly. CML always requires treatment when diagnosed. The abnormal cell that is producing the chronic leukaemia may also become unstable. Further changes in the cell may cause a blast crisis (becoming an acute leukaemia) leading to the production of only immature cells and a rapidly worsening condition.
Full blood count and differential
These are routine tests that are requested to count the number and relative proportion of each of the different types of cells in the blood stream. They give your doctor information about the relative maturity of the blood cells present and they can provide the first evidence that a person has leukaemia. Irregularities in cell counts, such as elevated WBC counts or low red blood cell counts may be due to leukaemia or to a variety of temporary or chronic conditions, but blasts (very immature WBCs) are not normally seen in the blood. If they are present, some kind of leukaemia is likely, and follow-up testing is indicated. The FBC and differential are used to help diagnose leukaemia and are important tools to monitor the effectiveness of treatment and to detect recurrence.
Bone marrow aspiration/biopsy
Bone marrow exists as a matrix of fibrous supporting tissue, fluid, undifferentiated stem cells, and a mixture of blasts and maturing blood cells. If your doctor suspects leukaemia, they will often request or perform a bone marrow aspiration or biopsy to look directly at the fluid and tissue in the marrow. A specialist then examines the marrow sample (bone and/or fluid) under the microscope, evaluating the number, size, and shape of each of the cell types, as well as the proportions of mature and immature cells. If leukaemia is present, the type and severity of the disease can be determined.
For more information, see Bone Marrow Aspiration and Biopsy.
Spinal tap (lumbar puncture)
If leukaemia is found in the bone marrow a lumbar puncture may also be done to look for leukaemia cells in the cerebrospinal fluid around the brain and spinal cord.
Cytogenetic analysis and fluorescent in-situ hybridization (FISH)
This is a molecular cytogenetic test used to investigate chromosomal abnormalities associated with leukaemias, other cancers, and genetic disorders. It is used for diagnosis and differentiating the leukaemias: there are translocations such as t(8;21) and many others for acute myeloblastic leukaemia t(15;17) for acute promyelocytic leukaemia and t(9;22) for chronic myeloid leukaemia. These techniques can also detect deletions associated with AML or myelodysplastic syndromes (5q, 7q) and trisomies (trisomy 12) for chronic lymphocytic leukaemia. Karyotyping and/or FISH helps diagnose different leukaemias that may look similar but have different genetic abnormalities and therefore may require different treatment.
Polymerase chain reaction (PCR)
This test amplifies DNA mutations, that are associated with certain leukaemias and may help with determining the prognosis for a certain leukaemia. Classic PCR tests look for for the promyelocytic leukaemia mutation PML-RARA (due to the chromosomal translocation t(15;17)(q22;21)], for the AML1-ETO fusion product (chromosomal translocation t(8;21)(q22;q22)) associated with acute myeloid leukaemia [and for (BCR-ABL (translocation t(9;22)) characteristic of chronic myeloid leukaemia. PCR screening tests look for a large number of known mutations.
Non-Laboratory Tests
Computerized tomography (CT), magnetic resonance imagine (MRI), or positron emission tomography (PET) scans are sometimes used to look for signs of the disease (tumours and masses of cells) in areas such as the chest. Other imaging scans may also be used to evaluate the status of body organs such as the spleen, liver, and kidney.
In general, cure and remission rates of leukaemia continue to improve for both children and adults.
Specific treatment depends on the type, severity, and symptoms. The goals of treatment are to address the cell shortages that are causing symptoms, push the leukaemia into remission, and, if possible, kill all of the abnormal white blood cells and therefore allow normal cells to reproduce and restore blood cell function.
Symptomatic treatment may include red blood cell and/or platelet transfusions and antibiotic therapy. If the spleen is too swollen, it may need to be surgically removed. Treatment of the leukaemia may include chemotherapy and steroidal drugs, antibody therapy and radiation. Both these treatments kill cells and relieve pain. In the case of CML, a specific non-chemotherapy class of drugs (tyrosine kinase inhibitors) has been designed to block the function of the abnormal protein produced by the bcr-abl mutation - which can control the disease for many years and perhaps indefinitely in some cases. The tablets are not apparently curative however.
If leukaemic cells have migrated into the cerebrospinal fluid, chemotherapy drugs that are injected directly into the spinal fluid may be required.
In some cases bone marrow or blood stem cell samples may be taken from the patient and frozen to be reintroduced into the same patient following treatment (autologous transplantation). Allogeneic bone marrow transplants (using a marrow sample from a compatible donor (usually a family member)) can be used to cure some cases of acute leukaemia. Bone marrow or peripheral blood stem cell transplants may be considered when other treatment regimens have failed to push the leukaemia into remission, or when the leukaemia has recurred.
Treatment and prognosis of chronic leukaemia depend upon which type a patient has: chronic lymphocytic leukaemia (CLL) or chronic myeloid leukaemia (CML). Researchers are continuing to investigate new therapies that may be useful in achieving remission and prolonging life. Patients with chronic lymphocytic leukaemia, however, may not need treatment for years if ever, e.g. not until the number of RBCs or platelets decreases. In addition, some therapies are associated with severe side effects that are worse than the patient's symptoms.