High amounts of ionizing radiation exposure can increase the risk of AML. Survivors of the atomic bombings of Hiroshima and Nagasaki had an increased rate of AML, as did radiologists exposed to high levels of X-rays prior to the adoption of modern radiation safety practices. People treated with ionizing radiation after treatment for prostate cancer, non-Hodgkin lymphoma, lung cancer, and breast cancer have the highest chance of acquiring AML, but this increased risk returns to the background risk observed in the general population after 12 years.

Leukemia is rarely associated with pregnancy, affecting only about 1 in 10,000 pregnant women. How it is handled depends primarily on the type of leukemia. Nearly all leukemias appearing in pregnant women are acute leukemias. Acute leukemias normally require prompt, aggressive treatment, despite significant risks of pregnancy loss and birth defects, especially if chemotherapy is given during the developmentally sensitive first trimester. Chronic myelogenous leukemia can be treated with relative safety at any time during pregnancy with Interferon-alpha hormones. Treatment for chronic lymphocytic leukemias, which are rare in pregnant women, can often be postponed until after the end of the pregnancy.

Exposure to anticancer chemotherapy, in particular alkylating agents, can increase the risk of subsequently developing AML. The risk is highest about three to five years after chemotherapy. Other chemotherapy agents, specifically epipodophyllotoxins and anthracyclines, have also been associated with treatment-related leukemias, which are often associated with specific chromosomal abnormalities in the leukemic cells.

Occupational chemical exposure to benzene and other aromatic organic solvents is controversial as a cause of AML. Benzene and many of its derivatives are known to be carcinogenic "in vitro". While some studies have suggested a link between occupational exposure to benzene and increased risk of AML, others have suggested the attributable risk, if any, is slight.

Some people have a genetic predisposition towards developing leukemia. This predisposition is demonstrated by family histories and twin studies. The affected people may have a single gene or multiple genes in common. In some cases, families tend to develop the same kinds of leukemia as other members; in other families, affected people may develop different forms of leukemia or related blood cancers.

In addition to these genetic issues, people with chromosomal abnormalities or certain other genetic conditions have a greater risk of leukemia. For example, people with Down syndrome have a significantly increased risk of developing forms of acute leukemia (especially acute myeloid leukemia), and Fanconi anemia is a risk factor for developing acute myeloid leukemia. Mutation in SPRED1 gene has been associated with a predisposition to childhood leukemia.

Chronic myelogenous leukemia is associated with a genetic abnormality called the Philadelphia translocation; 95% of people with CML carry the Philadelphia mutation, although this is not exclusive to CML and can be observed in people with other types of leukemia.

JMML accounts for 1-2% of childhood leukemias each year; in the United States, an estimated 25-50 new cases are diagnosed each year, which also equates to about 3 cases per million children. There is no known environmental cause for JMML. Since about 10% of patients are diagnosed before 3 months of age, it is thought that JMML is a congenital condition in these infants

Acute erythroid leukemia is rare, accounting for only 3–5% of all acute myeloid leukemia cases. One study estimated an occurrence rate of 0.077 cases per 100,000 people each year. 64–70% of people with this condition are male, and most are elderly, with a median age of 65.

CML accounts for 8% of all leukaemias in the UK, and around 680 people were diagnosed with the disease in 2011.

The exact cause of most cases of childhood leukemia is not known. Most children with leukemia do not have any known risk factors. The immune system plays an important role in protecting the body's immune system. An alteration or defect in the immune system may increase the risk for developing cancer. The immune system can be damaged by different factors, such as exposure to different viruses, environmental factors, chemical factors and other various infections.

There also appears to be some evidence linking childhood leukemia to x-ray exposure. In a 2010 study by the University of California, Berkeley’s School of Public Health, researchers found that children with acute lymphoid leukemia (ALL) had almost twice the chance of having been exposed to three or more X-rays compared with children who did not have leukemia.

Information on prognosis is limited by the rarity of the condition. Prognosis appears to be no different to AML in general, taking into account other risk factors. Acute erythroid leukemia (M6) has a relatively poor prognosis. A 2010 study of 124 patients found a median overall survival of 8 months. A 2009 study on 91 patients found a median overall survival for erythroleukemia patients of 36 weeks, with no statistically significant difference to other AML patients. AEL patients did have a significantly shorter disease free survival period, a median of 32 weeks, but this effect was explained by other prognostic factors. That is, AEL is often associated with other risk factors, like monosomal karyotypes and a history of myelodysplastic syndrome. Prognosis is worse in elderly patients, those with a history of myelodysplastic syndrome, and in patients who had previously received chemotherapy for the treatment of a different neoplasm.

Leukemia is rarely associated with pregnancy, affecting only about one in 10,000 pregnant women. Treatment for chronic lymphocytic leukemias can often be postponed until after the end of the pregnancy. If treatment is necessary, then giving chemotherapy during the second or third trimesters is less likely to result in pregnancy loss or birth defects than treatment during the first trimester.

Although not yet formally incorporated in the generally accepted classification systems, molecular profiling of myelodysplastic syndrome genomes has increased the understanding of prognostic molecular factors for this disease. For example, in low-risk MDS, "IDH1" and "IDH2" mutations are associated with significantly worsened survival.

CLL is primarily a disease of older adults, with a median age of 70 years at the time of diagnosis. Though less common, CLL sometimes affects people between 30 and 39 years of age. The incidence of CLL increases very quickly with increasing age.

In the United States during 2014, about 15,720 new cases are expected to be diagnosed, and 4,600 patients are expected to die from CLL. Because of the prolonged survival, which was typically about 10 years in past decades, but which can extend to a normal life expectancy, the prevalence (number of people living with the disease) is much higher than the incidence (new diagnoses). CLL is the most common type of leukemia in the UK, accounting for 38% of all leukemia cases. Approximately 3,200 people were diagnosed with the disease in 2011.

In Western populations, subclinical "disease" can be identified in 3.5% of normal adults, and in up to 8% of individuals over the age of 70. That is, small clones of B cells with the characteristic CLL phenotype can be identified in many healthy elderly persons. The clinical significance of these cells is unknown.

In contrast, CLL is rare in Asian countries, such as Japan, China, and Korea, accounting for less than 10% of all leukemias in those regions. A low incidence is seen in Japanese immigrants to the US, and in African and Asian immigrants to Israel.

Of all cancers involving the same class of blood cell, 7% of cases are CLL/SLL.

Rates of CLL are somewhat elevated in people exposed to certain chemicals. Under U.S. Department of Veterans' Affairs regulations, Vietnam veterans who served in-country or in the inland waterways of Vietnam and who later develop CLL are presumed to have contracted it from exposure to Agent Orange and may be entitled to compensation.

The American Cancer Society estimates that in 2014, about 5,980 new cases of chronic myelogenous leukemia were diagnosed, and about 810 people died of the disease. This means that a little over 10% of all newly diagnosed leukemia cases will be chronic myelogenous leukemia. The average risk of a person getting this disease is 1 in 588. The disease is more common in men than women, and more common in whites than African-Americans. The average age at diagnosis is 64 years, and this disease is rarely seen in children.

Some people have a history of exposure to chemotherapy (especially alkylating agents such as melphalan, cyclophosphamide, busulfan, and chlorambucil) or radiation (therapeutic or accidental), or both (e.g., at the time of stem cell transplantation for another disease). Workers in some industries with heavy exposure to hydrocarbons such as the petroleum industry have a slightly higher risk of contracting the disease than the general population. Xylene and benzene exposure has been associated with myelodysplasia. Vietnam veterans exposed to Agent Orange are at risk of developing MDS. A link may exist between the development of MDS "in atomic-bomb survivors 40 to 60 years after radiation exposure" (in this case, referring to people who were in close proximity to the dropping of the atomic bomb in Hiroshima and Nagasaki during World War II).

Children with Down syndrome are susceptible to MDS, and a family history may indicate a hereditary form of sideroblastic anemia or Fanconi anemia.

Prognosis refers to how well a patient is expected to respond to treatment based on their individual characteristics at time of diagnosis. In JMML, three characteristic areas have been identified as significant in the prognosis of patients:

Without treatment, the survival [5 years?] of children with JMML is approximately 5%. Only Hematopoietic Stem Cell Transplantation (HSCT), commonly referred to as a bone marrow or (umbilical) cord blood transplant, has been shown to be successful in curing a child of JMML. With HSCT, recent research studies have found the survival rate to be approximately 50%. Relapse is a significant risk after HSCT for children with JMML. It is the greatest cause of death in JMML children who have had stem cell transplants. Relapse rate has been recorded as high as 50%. Many children have been brought into remission after a second stem cell transplant.

Chloromas may occur in patients with a diagnosis of myelodysplastic syndrome (MDS) or myeloproliferative syndromes (MPS) (e.g. chronic myelogenous leukemia (CML), polycythemia vera, essential thrombocytosis, or myelofibrosis). The detection of a chloroma is considered "de facto" evidence these premalignant conditions have transformed into an acute leukemia requiring appropriate treatment. For example, presence of a chloroma is sufficient to indicate chronic myelogenous leukemia has entered its 'blast crisis' phase.

T-PLL is an extremely rare aggressive disease, and patients are not expected to live normal lifespans. Before the recent introduction of better treatments, such as alemtuzumab, the median survival time was 7.5 months after diagnosis. More recently, some patients have survived five years and more, although the median survival is still low.

About four men are diagnosed with this disease for every three women. Despite its overall rarity, it is also the most common type of mature T cell leukemia.

Leukemia is usually described either as "acute", which grows quickly, or "chronic", which grows slowly. One main type of acute leukemia is acute lymphocytic leukemia (ALL), which accounts for about 3 out of 4 cases of leukemia in children. ALL is a form of leukemia that affects the lymphocytes, a type of white blood cells which fights infection. When a patient has ALL, the bone marrow makes too many immature white blood cells and they do not mature correctly. Therefore, the white blood cells over-produce, crowding the other blood cells. The white blood cells also do not work correctly to fight infection.

Another type of acute leukemia is acute myelogenous leukemia (AML). AML is cancer of the blood in which too many myeloblasts, immature white blood cells, are produced in the bone marrow. The marrow continues to produce abnormal cells that crowd the other blood cells and do not work properly to fight infection. Almost all childhood leukemia is acute.

Chronic leukemias are more common in adults than in children, and although they tend to grow more slowly than acute leukemias, they are harder to treat. These chronic leukemias are divided into two types: chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL). CML is rare in children, but does occur and is treatable in children the same as in adults. CML patients have too many immature white blood cells being produced, and the cells crowd the other healthy blood cells.

A specific chromosome rearrangement is also found in patients with CML, among the 46 chromosomes in human cells. Part of chromosome nine breaks off and attaches itself to chromosome 22, meaning there is an exchange of genetic material between chromosomes 9 and 22. The rearrangement of the chromosomes changes the positions and functions of certain genes, which causes uncontrolled cell growth.

CLL is another form of chronic leukemia, but is extremely rare in children. Juvenile myelomonocytic leukemia (JMML) is a form of leukemia that is neither chronic nor acute and occurs most often in children under the age of four. JMML begins from myeloid cells, but is not as fast-growing as AML or as slow as CML.

At least one case of "FIP1L1-PDGFRA" fusion gene-induced eosinophilic leukemia presenting with myeloid sarcoma and eosinophilia has been reported. This form of myeloid sarcoma is distinguished by its highly successful treatment with imatinib (the recommended treatment for "FIP1L1-PDGRGA" fusion gene-induced eosinophilic leukemia) rather than more aggressive and toxic therapy.

Acute leukemia or acute leukaemia is a family of serious medical conditions relating to an original diagnosis of leukemia. In most cases, these can be classified according to the lineage, myeloid or lymphoid, of the malignant cells that grow uncontrolled, but some are mixed and for those such an assignment is not possible.

Forms of acute leukemia include:

- Acute myeloid leukemia

- Acute erythroid leukemia

- Acute lymphoblastic leukemia

- T-cell acute lymphoblastic leukemia

- Adult T-cell leukemia/lymphoma

- (Precursor)T-lymphoblastic leukemia/lymphoma

- "Blast crisis" of chronic myelogenous leukemia

Chronic leukemia is an increase of abnormal white blood cells. It differs from acute leukemia, and is categorized as myelogenous or lymphocytic.

Chronic leukemia may refer to:

- Chronic myelogenous leukemia

- Chronic lymphocytic leukemia

- Hairy cell leukemia

Acute mast cell leukemia is extremely aggressive and has a grave prognosis. In most cases, multi-organ failure including bone marrow failure develops over weeks to months. Median survival after diagnosis is only about 6 months.

The 5 year survival has been noted as 89% in at least one study from France of 201 patients with T-LGL leukemia.

Myeloid leukemia is a type of leukemia affecting myeloid tissue.

Types include:

- Acute myeloid leukemia

- Chronic myelogenous leukemia