Acute lymphoblastic leukemia - Article
Article: Acute lymphoblastic leukemia
Acute lymphoblastic leukemia (ALL), also known as acute lymphocytic leukemia, is a cancer of the white blood cells, characterised by the overproduction and continuous multiplication of malignant and immature white blood cells (referred to as lymphoblasts) in the bone marrow. It is a hematological malignancy. It is fatal if left untreated as ALL spreads into the bloodstream and other vital organs quickly (hence "acute"). It mainly affects young children and adults over 50.
Initial symptoms of ALL are quite aspecific, but worsen to the point that medical help is sought:
- Generalised weakness and fatigue
- Frequent or unexplained fever and infections
- Weight loss and/or loss of appetite
- Excessive bruising or bleeding from wounds, nosebleeds, petechiae (red pinpoints on the skin)
- Bone pain, joint pains (caused by the spread of "blast" cells to the surface of the bone or into the joint from the marrow cavity)
- Enlarged lymph nodes, liver and/or spleen
The signs and symptoms of ALL result from the lack of normal and healthy blood cells because they are crowded out by malignant and immature white blood cells. Therefore, people with ALL experience symptoms from their red blood cells, white blood cells, and platelets not functioning properly. Laboratory tests which might show abnormalities include blood counts, renal functions, electrolytes and liver enzymes.
Diagnosing leukemia usually begins with a medical history and physical examination. If there is a suspicion of leukemia, the patient will then proceed to undergo a number of tests to establish the presence of leukemia and its type. Patients with this constellation of symptoms will generally have had blood tests, such as a full blood count.
These tests may include complete blood count (blasts on the blood film generally lead to the suspicion of ALL being raised). Nevertheless, 10% have a normal blood film, and clinical suspicion alone may be the only reason to perform a bone marrow biopsy, which is the next step in the diagnostic process.
Bone marrow is examined for blasts, cell counts and other signs of disease. Pathological examination, cytogenetics (e.g. presence of the Philadelphia chromosome) and immunophenotyping establish whether the "blast" cells began from the B lymphocytes or T lymphocytes.
Lab tests (mentioned above) and clinical information may also be used to determine whether other medical imaging (such as ultrasound or CT scanning) may be required to find invasion of other organs such as the lungs or liver.
The etiology of ALL remains uncertain although some doctors believe that ALL develops from a combination of genetic and environmental factors. However, there is no definite way of determining the cause of leukemia.
Scientific research has shown that all malignancies are due to subtle or less subtle changes in DNA that lead to unimpaired cell division and breakdown of inhibitory processes. In leukemias, including ALL, chromosomal translocations occur regularly. It is thought that most translocations occur before birth during fetal development. These translocations may trigger oncogenes to "turn on", causing unregulated mitosis where cells divide too quickly and abnormally, resulting in leukemia. There is little indication that propensity for ALL is passed on from parents to children.
There have been indications that excessive exposure to high dose radiation (such as that of nuclear reactors, notably Chernobyl, and the atomic bombs in Hiroshima, Japan 1945) increases the risk of developing acute leukemia. There has also been inconclusive evidence suggesting that exposure to chemicals such as benzene can cause an increased risk for developing acute leukemia.
Subtyping of the various forms of ALL is done according to the FAB (French-American-British) classification, which is used for all acute leukemias (including acute myelogenous leukemia, AML). As ALL is not a solid tumour, the TxNxMx notation used in those cancers is of little use.
The FAB classification is:
- ALL-L1: small uniform cells
- ALL-L2: large varied cells
- ALL-L3: large varied cells with vacuoles (bubble-like features)
Note: The recent WHO International panel on ALL recommends that this classification be abandoned, since the morphological classification has no clinical or prognostic relevance. It instead, advocates the use of the immunophenotypic classification mentioned below.
Each subtype is then further classified by determining the surface markers of the abnormal lymphocytes, called immunophenotyping. There are three main immunologic types: B-cell, pre-B cell and T-cell. Subtyping helps determine the prognosis and most appropriate treatment in treating ALL.
Some cytogenetic subtypes have a worse prognosis than others. These include:
- A translocation between chromosomes 9 and 22, known as the Philadelphia chromosome, occurs in about 20% of adult and 5% in pediatric cases of ALL.
- A translocation between chromosomes 4 and 11 occurs in about 4% of cases and is most common in infants under 12 months.
- Not all translocations of chromosomes carry a poorer prognosis. Some translocations are relatively favourable.
The earlier acute lymphocytic leukemia is detected, the more effective the treatment. The aim is to induce a lasting remission, defined as the absence of detectable cancer cells in the body (usually less than 5% blast cells on the bone marrow).
Chemotherapy is the initial treatment of choice. Most ALL patients end up receiving a combination of different treatments. There are no surgical options, due to the body-wide distribution of the malignant cells.
As the chemotherapy regimens can be intensive and protracted (often about 2 years in case of the GMALL or UKALL protocols; about 3 years for males on COG protocols), many patients have an intravenous catheter inserted into a large vein (termed a central venous catheter or a Hickman line).
Radiation therapy is used on painful bony areas, in high disease burden, or as part of the preparations for a bone marrow transplant (total body irradiation). Radiation in the form of whole brain radiation is also used for central nervous system prophylaxis, to prevent recurrence of leukemia in the brain.
ALL accounts for approximately 80 per cent of all childhood leukemia cases, making it the most common type of childhood cancer. It has a peak incident rate of 2-5 years old, decreasing in incidence with increasing age before increasing again at around 50 years old. ALL is slightly more common in males than females.
Advancements in medical technology and research over the past four decades in the treatment of ALL has improved the overall prognosis significantly from a zero to 20-75 percent survival rate, largely due to the continuous development of clinical trials and improvements in bone marrow transplantation (BMT) and stem cell transplanation (SCT) technology.
- Sex: females tend to fare better than males.
- Ethnicity: Caucasians are more likely to develop acute leukemia than African-Americans, Asians and Hispanics and tend to have a better prognosis than non-Caucasians.
- Age at diagnosis: children between 1-10 years of age are most likely to be cured.
- Lymphoblast cell count at diagnosis
- Whether the cancer has spread to the brain or spinal cord
- Morphological, immunological, and genetic subtypes
- Response of patient to initial treatment
- Genetic disorders such as Down's Syndrome