Leukemia starts in the bone marrow but does not form a solid tumor like other types of cancer. By the time it is diagnosed, it has often spread to other areas in the body, such as the lymph nodes and spleen. Because of this, traditional staging systems that measure the size of the tumor, the involvement of lymph nodes, and the spread or metastasis, are not helpful. Instead, leukemia is classified by the characteristics of the type of leukemia. This information helps to predict how likely the leukemia is to respond to treatment.

Chronic lymphocytic leukemia

There are two main staging systems for chronic lymphocytic leukemia (CLL): the Rai classification and the Binet staging system.

Rai classification

• Stage I: Leukemia at this stage is considered low risk. There are too many white blood cells, but the lymph nodes are not enlarged.
• Stage II: Leukemia at this stage is considered intermediate risk. There are too many white blood cells, and the lymph nodes, liver, or spleen may be enlarged.
• Stage III/Stage IV: Leukemia at this stage is considered high risk. There are too many white blood cells and not enough red blood cells or platelets. The lymph nodes, liver, or spleen may be enlarged.

Binet staging

• Stage A: There are three or fewer areas of enlarged lymph tissue. Lymph nodes in one particular area, such as the neck or underarm, are considered one group, whether they occur on just one side of the body or on both sides.
• Stage B: There are more than three areas of enlarged lymph tissue.
• Stage C: Enlarged lymph tissue is present along with too few red blood cells (anemia) and platelets (thrombocytopenia).

Experts are studying new cancer markers, such as genetic changes and proteins on the surface of cells. This may help doctors tell what type of leukemia a person has. Knowing this can give an idea of how well treatment might work.

Acute leukemias

These classifications help determine the type of treatment and help to predict response to treatment.

• The classification for acute leukemias is called the French-American-British (FAB) classification. It is based on the appearance of the leukemic cells and by changes in the cells.
• Acute myelogenous leukemia (AML) is classified by the World Health Organization (WHO) on a scale of M0 to M7.
• Acute lymphoblastic leukemia (ALL) is classified on a scale of L0 to L3.