Causes
Doctors
classify leukemia in two ways. The first is by how fast the leukemia
progresses:
-
Acute leukemia.
In acute leukemia, the abnormal blood cells are immature blood cells
(blasts). They can't carry out their normal work, and they multiply
rapidly, so the disease worsens quickly. Acute leukemia requires
aggressive, immediate treatment.
-
Chronic leukemia.
This type of leukemia involves more mature blood cells. These blood
cells replicate or accumulate more slowly and can function normally for
a period of time. Some forms of chronic leukemia produce no symptoms and
can go unnoticed or undiagnosed for years.
-
The
second type of classification is by type of white blood cell affected:
-
Lymphocytic leukemia.
This type of leukemia affects the lymphoid cells or lymphocytes, which
form lymphoid or lymphatic tissue. This tissue is the main component of
the immune system and is found in places throughout your body, including
your lymph nodes, spleen and tonsils.
-
Myelogenous leukemia.
This type of leukemia affects the myeloid cells. The myeloid cell line
includes cells that later develop into red blood cells, white blood
cells and platelet-producing cells.
-
The major
types of leukemia are:
-
Acute myelogenous leukemia (AML).
This is the most common type of leukemia. It occurs in children and
adults. It's also called acute nonlymphocytic leukemia.
-
Acute lymphocytic leukemia (ALL).
This is the most common type of leukemia in young children. ALL accounts
for nearly 75 percent of all childhood leukemias.
-
Chronic myelogenous leukemia (CML).
This type of leukemia mainly affects adults. It's associated with a
chromosome abnormality called the Philadelphia chromosome. A person with
CML may have few or no symptoms for months or years before entering a
phase in which the leukemia cells grow more quickly.
-
Chronic lymphocytic leukemia (CLL).
With CLL, another common adult leukemia, you may feel well for years
without treatment. CLL is more common in Jewish people of Russian or
Eastern European descent. It almost never affects children.
Other,
rarer types of leukemia include hairy cell leukemia and chronic
myelomonocytic leukemia.
Doctors
don't understand the exact cause of leukemia. It seems to develop from a
combination of genetic and environmental factors.
Acute
leukemia begins with one or a few white blood cells that have a lost or
damaged DNA sequence. These cells remain immature in what's known as a
blast form, but maintain the ability to multiply. Because they don't
mature and then die as normal cells do, they accumulate and begin to
interfere with functions of vital organs. Eventually, they overwhelm the
production of healthy cells.
Chronic
leukemia involves more mature blood cells. They replicate and accumulate
more slowly, so the progression of the disease is slower but it can
still be deadly. Experts aren't sure why this process begins.
Whatever
the reason, having too few normal white blood cells eventually leads to
infection, anemia and excessive bleeding. Having too many abnormal white
blood cells can impair the function of bone marrow and infiltrate other
organs. Death usually results from bleeding or infection.
