Leukemia is a cancer of the blood cells. It is the most common type of blood cancer and affects 10 times as many adults as children. Most people diagnosed with leukemia are over 50 years old. Leukemia Starts in Bone Marrow Leukemia usually begins in the bone marrow, the soft material in the center of most bones where blood cells are formed. The bone marrow makes three types of blood cells, and each type has a special function. - White blood cells fight infection and disease.  - Red blood cells carry oxygen throughout the body.  - Platelets help control bleeding by forming blood clots. White blood cells fight infection and disease. Red blood cells carry oxygen throughout the body. Platelets help control bleeding by forming blood clots. In people with leukemia, the bone marrow produces abnormal white blood cells, called leukemia cells. At first, leukemia cells function almost normally. But over time, as more leukemia cells are produced, they may crowd out the healthy white blood cells, red blood cells, and platelets. This makes it difficult for the blood to carry out its normal functions. There are four common types of adult leukemia. Two are chronic, meaning they get worse over a longer period of time. The other two are acute, meaning they get worse quickly. - chronic lymphocytic leukemia  - chronic myeloid leukemia  - acute myeloid leukemia  - acute lymphocytic leukemia chronic lymphocytic leukemia chronic myeloid leukemia acute myeloid leukemia acute lymphocytic leukemia Chronic and Acute Leukemia Chronic lymphocytic leukemia, chronic myeloid leukemia, and acute myeloid leukemia are diagnosed more often in older adults. Of these, chronic lymphocytic leukemia is the most common. Acute lymphocytic leukemia is found more often in children. The symptoms for each type of leukemia differ but may include fevers, frequent infections, fatigue, swollen lymph nodes, weight loss, and bleeding and bruising easily. However, such symptoms are not sure signs of leukemia. An infection or another problem also could cause these symptoms. Only a doctor can diagnose and treat the problem. (Watch the video to learn how the rates of leukemia diagnosis vary by age. To enlarge the video, click the brackets in the lower right-hand corner. To reduce the video, press the Escape (Esc) button on your keyboard.)  Learn more about chronic lymphocytic leukemia.  Learn more about acute myeloid leukemia.  Other Cancers That Affect Blood Cells Myeloma and lymphoma are other types of cancer that affect blood cells, but these cancer cells are rarely found in the blood stream. Myeloma is the second most common form of blood cancer, and it affects plasma cells, a type of white blood cell that is found in the bone marrow. Lymphoma accounts for about five percent of all the types of cancer in the United States. It starts in the lymphatic system, which is part of the body's immune system. Both myeloma and lymphoma are more common among older adults and occur more often in men than women.  Learn more about myeloma.  Many Treatments Are Available There are many methods available to treat acute and chronic leukemia, and there are many new treatments being developed that are rapidly changing how numerous types of leukemia are treated. The types of treatments depend on the specific disease and how best to treat it. Some people receive a combination of treatments. Acute leukemia usually needs to be treated right away. But there are many different kinds of acute leukemia. Some respond well to treatment and can be cured in some cases, while others are more difficult to treat. Treatment for chronic leukemia can often control the disease and its symptoms and there are new treatments being developed that may prolong survival. Also, there are several treatments now available for chronic myeloid leukemia that can control the disease for a long time.