Leukemia begins in the bone marrow and multiplies just like other cells. Lymphocytic or lymphoblastic leukemias come from bone marrow cells that form lymphocytes—white blood cells that are part of the immune system. Different kinds of lymphocytes do different things:
- B lymphocytes produce antibodies that help combat bacterial, fungal or viral infections
- T lymphocytes have several functions, including helping B lymphocytes make antibodies
- Natural killer (NK) cells attack virus-infected cells or tumor cells
Myelogenous or myeloid leukemias occur in bone marrow cells that normally become red cells, some white cells and platelets.
Leukemia cells grow and survive better than normal cells, and over time they crowd out normal cells. The rate at which leukemia progresses and how the cells replace the normal blood and marrow cells are different with each type of leukemia.
When it’s acute, leukemia quickly prevents a large proportion of early blood cells from maturing. In chronic leukemia, more healthy blood cells get a chance to mature, so symptoms usually come on more gradually, and they are less severe at first.
Original acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML) cells cells come from immature blood cells. They make about a trillion leukemia cells that don’t work like normal cells and that crowd out normal cells in the bone marrow. Red cell counts drop, and the patient becomes anemic.
In chronic myelogenous leukemia (CML), the leukemia cell that starts the disease still makes red and white blood cells and platelets that work almost like normal cells. Red cell counts are usually less than normal, but many white cells and platelets are still being produced. Even though the white cells are nearly normal in how they work, their numbers are high and they continue to rise. This can cause serious problems if the patient does not get treatment. If untreated, the white cell count can rise so high that blood flow slows down and anemia becomes severe.
In chronic lymphocytic leukemia (CLL), the leukemia cell that starts the disease makes too many non-functioning lymphocytes. These replace normal cells in the bone marrow and lymph nodes, and they interfere with the normal lymphocytes, so the person’s immune response become weakened. The high number of leukemia cells in the marrow may crowd out normal blood-forming cells and lead to a low red cell count. A very high number of leukemia cells building up in the marrow also can lead to low neutrophil and platelet counts.
Unlike the other three types of leukemia, some patients with CLL may have disease that does not progress for a long time. Some people with CLL have such slight changes that they remain in good health and do not need treatment for long periods of time. Most patients require treatment at the time of diagnosis or soon after.
Find out the most common symptoms of leukemia, how the disease is diagnosed and who's at increased risk.