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

If you are being treated for chronic myeloid leukemia (CML), your doctor will check your blood counts, examine you, and do other tests like bone marrow biopsies and lab tests of blood and/or bone marrow samples. (These tests are discussed in Tests for Chronic Myeloid Leukemia.)

These check-ups will be at least every 3 months for at least the first year of treatment. They're done to see how well the CML is responding to treatment. If the CML is not responding, you may need to switch to another drug.

Studies have suggested that a fast response (within 3 to 6 months) is linked to better outcomes.

Doctors look for different kinds of responses to treatment.

Hematologic response

Hematologic response is based mainly on if the numbers of cells in your blood have returned to normal. The main test used to measure this is a complete blood count (CBC). It's done on a sample of blood taken from your arm.

• Complete hematologic response (CHR): This means your white blood cell and platelet counts have returned to normal, there are no immature cells seen in your blood, and your spleen is back to a normal size.

Cytogenetic response

Cytogenetic response is based on the percentage of cells in a sample of your bone marrow that have the Philadelphia chromosome (and therefore are CML cells). This can be determined with either cytogenetics or FISH testing, both of which can find altered (mutated) chromosomes.

• A major cytogenetic response means no more than 35% of the cells in the bone marrow have the Philadelphia chromosome. A major response can be either complete or partial:
  • A complete cytogenetic response means no (or less than 1% of) cells in the bone marrow have the Philadelphia chromosome.
  • A partial cytogenetic response means between 1% and 35% of the cells in the bone marrow still have the Philadelphia chromosome.

• A minor cytogenetic response means that 36% to 65% of the cells in the bone marrow still have the Philadelphia chromosome.
• A minimal cytogenetic response means that 66% to 95% of the cells in the bone marrow still have the Philadelphia chromosome.
• No response means that more than 95% of the bone marrow cells still have the Philadelphia chromosome.

Molecular response

Molecular response is based on how much of the BCR-ABL gene (which is found in CML cells) can be detected by the PCR test. This test can be done on either your blood or bone marrow.

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

You may hear the terms long-term deep molecular response or durable complete molecular response. This is a long-lasting complete molecular response. It's the goal of CML treatment.