Leukemia is cancer of the developing blood cells, also known as blasts, in the bone marrow. Leukemia leads to rampant overproduction of precursor white blood cells (leukocytes); symptoms usually include anemia, fever, enlarged liver, spleen, and/or lymph nodes.
Leukemias are differentiated by the type of white blood cell involved, and the speed at which they develop. Myeloid leukemias are derived from blasts in the myeloid linage (producing macrophages, granuloctes), whereas lymphoid or lymphoblastic leukemias are derived from blasts in the lymphoid linage (producing B, T and NK lymphoid cells). Acute leukemias develop over a period of weeks to a couple of months, and are rapidly fatal if untrated. Chronic leukemias develop over years, and can generally be treated with supportive treatment and single agent chemotherapies. Chronic leukemias have the risk of undergoing a transformation to an acute leukemia, known as an acute blast crisis.
The four most common types of leukemia are:
- acute myeloid leukemia (AML) - peaks in the older age groups, poorer prognosis
- acute lymphoblastic leukemia (ALL) - peaks in children, more likely to have brain involvement
- chronic myeloid leukemia (CML)
- chronic lymphoid leukemia (CLL)
The effects of leukemias are due to the displacement of normal cell linages in the bone marrow, and the infiltration of other organs. These include:
- anaemia - a deficiency in red blood cells, reducing the oxygen carrying capacity of the blood producing lethargy, and increasing the risk of hypoxic events (such as acute coronary syndrome)
- leukipenia - a deficiency in white blood cells, reducing the body's ability to fight infection
- thrombocytopenia - a deficiency in platelets, increasing the risk of bleeds; less common than the others
- lymphadenopathy - due to involvement of the lymph nodes
- hypersplenism - due to the breakdown of blasts, can cause sequestration of normal cells and increases the risk of disseminated intravascular coagulopathy (a clotting disorder)
- boney involvement - causing bone pain and pathological fractures (more common in other malignancies)
- leukemic cutis - skin lesions, often not problematic in themselves but a marker of the disease
- leptomeningeal disease - infiltration of the meninges surrounding the brain, can cause a mass effect resulting in focal neurological deficiencies and, if untreated, herniation
The mainstay of treatment for leukemia is chemotherapy. Cytotoxic agents are introduced into the body which affect rapidly dividing cells, including cancer cells, resulting in their death. A patient will often undergo several cycles of chemotherapy, administered according to strict protocols. For example, AML is commonly treated with induction chemotherapy (under the 7:3 protocol), and then several cycles of consolidation chemotherapy (under the HiDAC protocol). Chemotherapy is often administered into the spinal cord and brain through intrathecal chemotherapy, particularly for ALL.
These affect rapidly dividing cells, including not only leukemia cells, but also normal blood cells, hair, and the mucosal surfaces lining the gastrointestinal tract. This produces a number of side effects, including a pancytopenia (high risk of infection and bleeding), nausea, vomiting, diarrhoea and hair loss. The mortality rate from chemotherapy is approximately 3-4%, the majority of these deaths due to infection. Patients are closely monitored following a cycle, and if they become febrile are treated with powerful IV antibiotics.
Leukemias do not have a single cause. A variety of agents are believed to produce a cumulative effect increasing the risk of cancer. This includes a person's genes, exposure to a variety of industrial chemicals, exposure to previous radiotherapy and chemotherapy, and viruses.
Acute leukemias are always fatal if not treated, death usually being caused by internal hemorrhage and/or serious infections. Chronic leukaemias can occur for years without complications, and death most commonly occurs with an acute blast crisis. Leukemias occurring in children are significantly more curable than those occurring in older adults.
- Human Anatomy and Physiology, by Elaine Maries, Benjamin/Cummings Publishing, 1995