Pathology refers to the careful examination of tissue under a microscope to find out whether it's cancerous or non-cancerous and to determine the type of cancer it is. Leukemia is a cancer that starts in the blood-forming cells of the bone marrow. It usually affects the white blood cells. However, other blood cells can also be involved.
Leukemia results from changes to the DNA of the stem cells in the bone marrow. These changes affect the growth and development of the changed cell. The leukemia cells crowd out the normal blood cells in the bone marrow, lowering production and function of normal blood cells.
The type of leukemia depends on the type of white blood cell from which it developed and whether it is fast growing or slow growing.
Lymphocytic and myelogenous leukemia
Leukemia can develop from different types of white blood cells.
- Lymphocytic leukemia starts in the early forms of lymphocytes (lymphoid stem cells).
- Myelogenous leukemia starts in the early forms of the myeloid cells (myeloid stem cells).
Acute and chronic leukemia
Acute and chronic leukemia differ in the number of mature blood cells. Acute leukemias have an increased number of immature cells. Chronic leukemias have an increased number of mature cells.
- acute leukemia
- The cells in the bone marrow do not mature the way they should. These immature (underdeveloped) cells continue to reproduce, build up and crowd out normal cells.
- Acute leukemia progresses rapidly so there are more immature cells than mature cells. The immature cells cannot carry out the normal functions of the blood cells.
- chronic leukemia
- The cells in the bone marrow partly mature and look more normal than the immature cells of acute leukemia.
- Chronic leukemia usually progresses slowly and allows more cancerous cells to develop. These cells survive longer, so they build up and crowd out normal cells. Generally, these cells can carry out some of their normal functions.
Types of leukemia
Leukemias are divided into 4 main groups:
- acute lymphocytic (or lymphoblastic) leukemia (ALL)
- chronic lymphocytic (or lymphoid) leukemia (CLL)
- acute myelogenous (or myeloid) leukemia (AML)
- chronic myelogenous (or myeloid) leukemia (CML)
- considered a chronic myeloproliferative disorder
Rare lymphocytic leukemias
Several types of rare lymphocytic leukemia share some characteristics with CLL:
Related disorders
Myeloproliferative disorders
In myeloproliferative disorders (MPD), the body overproduces (makes large amounts of) 1 or more types of blood cells (red blood cells, white blood cells or platelets). The overproduction starts when a single stem cell mutates and reproduces. There are 4 types of myeloproliferative disorders:
Myelodysplastic syndromes
Myelodysplastic syndromes (MDS) are a group of diseases in which the bone marrow does not make enough healthy mature blood cells. The immature cells, called blasts, do not function properly. They collect and build up in the bone marrow and the blood. As a result, there are fewer healthy red blood cells, white blood cells and platelets.
Myelodysplastic/myeloproliferative diseases
Myelodysplastic/myeloproliferative diseases have characteristics of both myelodysplastic syndromes and myeloproliferative disorders.
Once the type of leukemia or related disorder has been diagnosed, the doctor will also consider:
- the phase or classification of the leukemia or disorder
- the progression of the disease (where it has spread)
- prognostic factors (special characteristics that might influence the course of the disease)
- survival statistics for the particular type of leukemia or disorder
All of this information helps the doctor make a treatment plan.
See a list of questions to ask your doctor about pathology and staging.