Stages of acute myeloid leukemia

Staging describes or classifies a cancer based on how much cancer there is in the body and where it is when first diagnosed. This is often called the extent of cancer. For solid tumours, information from tests is used to find out the size of the tumour, which parts of the organ have cancer, whether the cancer has spread from where it first started and where the cancer has spread. Your healthcare team uses the stage to plan treatment and estimate the outcome (your prognosis).

Leukemia does not usually form solid tumours, and so staging is different.

Acute myeloid leukemia (AML) is described as untreated, active disease, in remission, measurable residual disease (MRD), relapsed (also called recurrent) or refractory. Doctors use these terms and others to describe leukemia when talking about treatment and response to treatment.

Untreated AML means that the leukemia is newly diagnosed and hasn’t been treated yet. Untreated AML is defined by the following:

• There are low numbers of normal blood cells (red blood cells, white blood cells and platelets).
• Immature blood cells may be seen in the blood sample. Immature blood cells are called blast cells, or blasts. When leukemia is diagnosed, they are called leukemia cells.
• At least 20% of the cells in the bone marrow are blast cells.
• There are usually signs and symptoms of AML.

Doctors use a complete blood count (CBC) to check the numbers of different types of blood cells.

Active disease means that more than 5% of the cells in the bone marrow are blasts. This term may be used during or after treatment if the disease has come back.

After AML is treated, the leukemia can be in remission.

Complete remission (complete response) means that all of these criteria apply:

• The numbers of blood cells (neutrophils and platelets) have recovered to an absolute neutrophil count greater than 1 x 10⁹/L and a platelet count greater than 100 x 10⁹/L, without blood transfusion.
• Less than 5% of the cells in the bone marrow are blast cells.
• There are no general signs or symptoms of AML, such as fatigue, weight loss, fever, anemia or bleeding.
• There are no signs or symptoms of leukemia in the brain and spinal cord (called the central nervous system, or CNS) or anywhere else in the body.

Partial remission means that less than 25% of the cells in the bone marrow are blast cells and that the bone marrow is functioning normally.

After treatment, there may still be blasts in the bone marrow. Standard lab tests, such as microscopy, may not find these leukemia cells. But more sensitive tests, such as flow cytometry or polymerase chain reaction (PCR), can find them. Disease that can only be found using more sensitive tests is called measurable residual disease (MRD). It is also known as minimal residual disease.

MRD can be used to measure response to treatment. People with small amounts of MRD may have a greater risk of the cancer coming back than people with undetectable MRD.

Relapsed (recurrent) AML means the leukemia has come back after treatment and remission. Relapse means that the percentage of blast cells is above 5% and is continuing to increase.

Refractory disease means the leukemia did not respond to the most recent treatment.