Acute lymphocytic leukemia is uncommon among adults -- about 2,410 will develop the disease in the United States this year -- but ALL is the most common childhood cancer. Among adults, the incidence of ALL increases with age. ALL is less common among African Americans than among whites although scientists are unsure why. (For information about our services for children with leukemia, please visit Pediatric Leukemias.)
How ALL Develops
Like other blood cells, lymphocytes evolve from immature cells called hematopoietic stem cells. Stem cells are produced in the bone marrow and usually mature, or differentiate, into one of a range of different kinds of blood cells. Lymphocytic stem cells mature into T lymphocytes (T cells), B lymphocytes (B cells), or natural killer (NK) cells. Each of these has a specialized role in the immune system. Normal, healthy lymphocytes evolve through their life cycle in an orderly way and eventually die, to be replaced by new cells.
In acute lymphocytic leukemia (ALL) the DNA of the diseased cells is damaged, and the cells cannot mature beyond an early stage in their life cycle to become functional. Instead, the immature cells (called leukemic blasts or lymphoblasts) reproduce rapidly, take over the bone marrow, and displace the normal red and white blood cells and platelets that are produced there. As the numbers of normal cells fall, patients may experience anemia (a lack of oxygen-carrying red blood cells); infections caused by low counts of disease-fighting white blood cells; and bruising and bleeding resulting from low levels of platelets (the blood component that plays a crucial role in blood clotting and wound healing). Leukemic cells may also invade the liver, spleen, lymph nodes, and other organs.
