Leukamia

Leukemia
I   INTRODUCTION

Leukemia, any of several types of cancers that affect blood cells, including oxygen-carrying red cells; certain infection-fighting white cells, such as granulocytes, macrophages and lymphocytes; and platelets, which aid in blood clotting. According to the American Cancer Society, leukemia is the sixth leading cause of cancer deaths among men and the seventh leading cause of cancer deaths among women. Each year in the United States about 31,000 new cases of leukemia are diagnosed and the disease causes an estimated 22,000 deaths. It accounts for about one-third of all cancers in children under age 15.

Blood cells are made in the bone marrow, the spongy tissue in the center of bones. A leukemia begins when an immature blood cell in the marrow, known as a progenitor cell, becomes cancerous, dividing uncontrollably and overriding the body’s normal restrictions on cell division. Over time, the marrow becomes crowded with cancerous cells, all of them descendants of the first abnormal cell. The malignant cells may also accumulate in a patient’s lymph nodes, spleen, and elsewhere. At the time of diagnosis, up to a trillion leukemic cells may be present in the body.

The mass of leukemic cells in the marrow suppresses the production of healthy blood cells, giving rise to the symptoms typical of leukemia. Pale skin, fatigue, and shortness of breath are signs of anemia, a decrease in the concentration of red cells in the blood. Nose bleeds, gum bleeding, a tendency to bruise easily, and pinhead-sized red spots on the skin reflect the decrease in the concentration of platelets in the blood. A lack of functional white cells makes patients with leukemia prone to infection.

Leukemia was first described by European physicians during the mid-19th century. During autopsies, physicians noted cases of profoundly elevated white cell counts—today we know that many of these white cells were nonfunctional leukemic cells—and very low red cell counts....