Leukemia, also spelled leukaemia, is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called blasts or leukemia cells. Symptoms may include bleeding and bruising, fatigue, fever, and an increased risk of infections. These symptoms occur due to a lack of normal blood cells. Diagnosis is typically made by blood tests or bone marrow biopsy.
The exact cause of leukemia is unknown. A combination of genetic factors and environmental (non-inherited) factors are believed to play a role. Risk factors include smoking, ionizing radiation, some chemicals (such as benzene), prior chemotherapy, and Down syndrome. People with a family history of leukemia are also at higher risk. There are four main types of leukemia—acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML)—as well as a number of less common types. Leukemias and lymphomas both belong to a broader group of tumors that affect the blood, bone marrow, and lymphoid system, known as tumors of the hematopoietic and lymphoid tissues.
Treatment may involve some combination of chemotherapy, radiation therapy, targeted therapy, and bone marrow transplant, in addition to supportive care and palliative care as needed. Certain types of leukemia may be managed with watchful waiting. The success of treatment depends on the type of leukemia and the age of the person. Outcomes have improved in the developed world. Five-year survival rate is 57% in the United States. In children under 15, the five-year survival rate is greater than 60% or even 90%, depending on the type of leukemia. In children with acute leukemia who are cancer-free after five years, the cancer is unlikely to return.
In 2015, leukemia was present in 2.3 million people worldwide and caused 353,500 deaths. In 2012 it newly developed in 352,000 people. It is the most common type of cancer in children, with three-quarters of leukemia cases in children being the acute lymphoblastic type. However, over 90% of all leukemias are diagnosed in adults, with CLL and AML being most common in adults. It occurs more commonly in the developed world.
Leukaemia is four times more common in industrialized countries than in poorer ones. During the period 1955 to 1989, deaths in the EEC/EU from leukaemias fell by an average of 26% for males and 33% for females, with a greater drop in child mortality. This is attributed to chemotherapy. Over the same period in eastern European countries, the the decrease in leukaemia deaths was an average of 10%.
In the UK approximately 1,200 children each year develop leukaemia. Studies have shown a link between both ionizing and non-ionizing radiation and childhood cancers, raising the possibility that workers' sperm was damaged and could produce children with leukaemia. Excessive incidence of cancer have been reported in proximity to nuclear installations. Such clusters have been shown to be real and not the result of chance. Leukaemia clusters have also been shown to be associated with incidence of population movement, even where there are no nuclear installations. There are also suggestions that men who received more than 100 millisieverts of radiation over a lifetime, especially if they had been exposed in the six months prior to conception, had 6 to 8 times the possibility of producing a child with leukaemia because of mutation of sperm.