Phases of childhood leukemia

Childhood leukemia has no standard staging system but can be described using phases. The phases of childhood leukemia are described as untreated, in remission, relapsed (recurrent) and refractory. Doctors use these terms and others to describe childhood leukemia when talking about treatment and response to treatment.

Untreated childhood leukemia means that the leukemia is newly diagnosed and hasn’t been treated yet. Untreated childhood leukemia means that one or more of the following apply:

• There may be low numbers of normal blood cells (red blood cells, white blood cells and platelets).
• For acute lymphocytic leukemia (ALL), usually more than 25% of the cells in the bone marrow are blasts (immature white blood cells).
• For acute myelogenous leukemia (AML), usually more than 20% of the cells in the bone marrow are blasts.
• There are signs and symptoms of childhood leukemia.

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

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

Complete remission (complete response) means that all of the following apply:

• The numbers of blood cells (red blood cells, white blood cells and platelets) are normal or close to normal.
• Less than 5% of the cells in the bone marrow are blasts.
• There are no general signs or symptoms of childhood leukemia, such as fatigue, weight loss, fever, anemia or bleeding.
• There are no signs or symptoms of childhood 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 blasts.

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 minimal residual disease (MRD).

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

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.

Recurrent (relapsed) disease means that leukemia has come back after it was in remission following treatment. A child is considered to have recurrent leukemia if more than 5% of the cells in the bone marrow are blasts.

Leukemia may come back in the blood, bone marrow or other parts of the body, such as the CNS. It may also come back in the testicles in boys.

Refractory disease means that the cancer is resistant to treatment or the treatment isn’t working. A child is considered to have refractory disease if the leukemia doesn’t go into complete remission after treatment.

Central nervous system (CNS) disease is when leukemia has spread to the brain or spinal cord. It is defined by the number of white blood cells (WBCs) in the cerebrospinal fluid (CSF).

CNS disease means one of the following:

• CNS 1 – no blasts in the CSF
• CNS 2 – WBC count is less than 5/mL with blasts in the CSF
• CNS 3 – WBC count is 5/mL or greater with blasts in the CSF or there are signs that leukemia has spread to the CNS