Leukemia, also spelled leukaemia, maybe a group of blood cancers that sometimes begin within the bone marrow and end in high numbers of abnormal blood cells. These blood cells aren't fully developed and are called blasts or leukemia cells. Symptoms may include bleeding and bruising, feeling tired, fever, and an increased risk of infections. These symptoms occur thanks to a scarcity of normal blood cells. Diagnosis is usually 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 task. Risk factors include smoking, radiation, some chemicals (such as benzene), prior chemotherapy, and mongolism. People with a case history of leukemia also are at higher risk. There are four main sorts of leukemia—acute lymphocytic leukemia (ALL), acute chronic myelocytic leukemia (AML), chronic leukemia (CLL), and chronic myelocytic leukemia (CML)—as well as a variety of less common types. Leukemias and lymphomas both belong to a broader group of tumors that affect the blood, bone marrow, and lymphoid system referred to as tumors of the hematopoietic and lymphoid tissues.