Leukemia is a type of cancer that affects the bone marrow, causing an excessive number of abnormal leukocytes to be produced. Leukemia can be classified as lymphoid or myeloid, depending upon the lineage of WBCs which it affects. Leukemia can further be stratified as acute or chronic; if it primarily affects immature WBCs it is acute, if it affects mature leukocytes it is chronic. Acute leukemias typically affect a younger population and are more aggressive, whereas chronic leukemia is characteristically a disease of the elderly and develop slowly. The four key types of leukemia are: acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML). In addition, there are number of rarer types, including acute promyelocytic leukemia (APL) and hairy cell leukemia.

Leukemia represents around 3.7% of all new cancer cases and 4.1% of cancer-related deaths in the US, and around 3% of new cancer cases and cancer-associated mortality in the UK. The NIH reports that 60.6% of people survive 5 years or more after a diagnosis of leukemia (based on data from SEER 18 2007-2013). The causes of leukemia are not fully understood, although a variety of genetic, epigenetic and environmental factors are thought to serve a role. Smoking, ionizing radiation, certain chemicals and prior chemotherapy have all been associated with leukemogeneis. Since the early 1990s, the incidence rates of leukemia have gradually increased, for which many reasons could be speculated.

Treatment usually comprises a combination of standard chemotherapy, radiotherapy, targeted therapy and bone marrow transplant. Exciting novel therapies for the treatment of leukemias are being researched, including immunotherapies, such as CAR T-cells and bispecific antibodies, in addition to novel combination regimens.