Leukemia or leukemia is a cancer of the blood or bone marrow. In most cases, the main symptoms are abnormal proliferation of white blood cells , usually white blood cells. The name of the disease is derived from - Luke ~ meaning white , Hemo ~ meaning blood. These white blood cells circulating in the blood are immature and ineffective. As a result of their proliferation in the blood-producing bone marrow, normal blood cell production is disrupted locally. However, not all leukemia has a high white blood cell count. In some cases, leukemia or sub-leukemia (almost normal number of white blood cells) can be seen (such as in the case of "hair cell leukemia"). Therefore , leukemia is caused by abnormalities of blood cells , not by numbers.