Response to treatment

Haematologists classify CML patients’ response to treatment in a number of ways:

Complete haematological response:

  • Blood cell counts have returned to normal (white blood cells less than 10´109/L; platelets less than 10´109/L
  • Less than 5% of leukaemia cells present in the bone marrow
  • This response is usually the first improvement to happen. Haematologists anticipate this response by six months of treatment.


Complete cytogenetic response: There are no cells with the Philadelphia chromosome detected in the body.

Complete molecular response: No detection of BCR-ABL1 anywhere in the body, even when using the sensitive PCR test, i.e., No MRD.

Haematologists advise that ‘complete molecular response’ should no longer be used. It should be replaced with Major molecular response (MMR) with specification of the level of BCR-ABL1 detected. This provide more information for patient management.

Major molecular response (MMR or MR3)

  • MMR3 is defined as detection of BCR‑ABL ≤1%. This should be done using PCR where possible (Hochhaus et al 2020).
  • MMR can be further refined to MR4 or MR4.5 as follows (Saglio and Gale 2020):
  • MMR4: BCR-ABL1 levels ≤01%.
  • 5: BCR-ABL1 levels ≤0.0032%
  • 5 is often required as a requirement for discontinuing a TKI for example