How Do You Know If Treatment for Chronic Myeloid Leukemia Is Working?

If you have chronic myeloid leukemia (CML) and are being treated with targeted drugs, your doctor will check your blood counts, examine you, and will order other tests like bone marrow biopsy and PCR (of blood and/or bone marrow). Doctors look for different kinds of responses to treatment:

Hematologic response is based on the complete blood count, and usually happens within the first 3 months of treatment.

• When blood cell counts return to normal, there are no immature cells seen in the blood, and the spleen has returned to normal size it is called a complete hematologic response (or CHR).
• A partial hematologic response means that there has been some improvement, but there are still signs or symptoms of CML. The white blood cell count is less than half of what it was before treatment, the platelet count is still high but is may be less than half what it was before treatment, and/or the spleen is still enlarged (but it has shrunk in size).

Cytogenetic response is based on testing of the bone marrow with either cytogenetics or FISH (these were discussed in How Is Chronic Myeloid Leukemia Diagnosed?). This takes longer to occur than the hematologic response.

• A complete cytogenetic response (CCyR) occurs when no cells with the Philadelphia chromosome can be found in the bone marrow.
• A partial cytogenetic response (PCyR) occurs when 1% to 34% of cells still have the Philadelphia chromosome.
• A major cytogenetic response (MCyR) includes both complete and partial responses, and means less than 35% of cells have the Philadelphia chromosome
• A minor cytogenetic response occurs when 35% to 90% of cells still have the Philadelphia chromosome.

Molecular response is based on the results of the PCR test on either the blood or bone marrow

• A complete molecular response (CMR) means that the PCR test does not find the BCR-ABL gene in the patient's blood.
• A major molecular response (MMR) means that the amount of BCR-ABL gene in the blood is 1/1000^th (or less) of what is expected in someone with untreated CML.