Leukemia develops in the bone marrow and quickly travels to the blood. From there, leukemia can spread to other parts of the body, such as the lymph nodes, spleen, liver, central nervous system, and other organs. Leukemia is classified into two categories: acute and chronic. Acute leukemia develops quickly and produces abnormal cells rapidly. In chronic leukemia cases, the abnormal cells are more mature and can still carry out some of their normal functions. Chronic leukemia develops more slowly than acute.