Leukemia (also spelled leukaemia; pronounced loo-KEE-mee-ə) is a group of blood cancers that usually begin in the bone marrow and produce 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, bone pain, 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, petrochemicals (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)—and 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, with supportive and palliative care provided 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 was 67% in the United States in the period from 2014 to 2020. In children under 15 in first-world countries, the five-year survival rate is greater than 60% or even 90%, depending on the type of leukemia. In children who are cancer-free five years after diagnosis of acute leukemia, 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 had 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, CLL and AML being most common. It occurs more commonly in the developed world. Source: Wikipedia (en)