Hematological Response is a normalization of the blood counts, particularly white blood cell counts. This is the first noticeable indicator that treatment is beginning to work, though not necessarily in the bone marrow. The response can be partial HR (reduction in white cells,but not down to normal range) or complete CHR (white blood count at or below approximately 12,000 white cells/microliter).

Your doctor will anticipate CHR within the first three months of treatment, however, some patients may take longer to achieve this level.  During the early stages of treatment, your physician will monitor you closely to keep track of the response and determine if the correct course of treatment is in place.  The majority of patients easily achieve this milestone on or before the three month mark.

For detailed monitoring information see Monitoring & Tests

Cytogenetic Response is a response to treatment of CML that occurs in the marrow, rather than just in the blood.

There are 3 levels of cytogenetic response:

1) Cytogenetic response (CR or CyR): A cytogenetic response means any Ph+ chromosome reading less than what you began with at diagnosis;

2) Major cytogenetic response (MCR or MCyR); Major means 35% or less of the cells in your marrow test positive for the Philadelphia chromosome, but more than 0%;

3) Complete cytogenetic response (CCR or CCyR): Complete cytogenetic response means no Ph+ cells can be measured by either conventional or FISH cytogenetic testing (though the PCR test may still be positive).

Molecular Response is defined as a negative PCR or other negative molecular test.  Molecular responses can only be measured using a Polymerase Chain Reaction/PCR test.  A PCR test is defined as a very sensitive test which can be used to detect the presence of very low levels of specific genetic material (DNA).  It is used to detect, and sometimes to quantify, bcr-abl in bone marrow cells of patients with CML. The most sensitive PCR tests can detect as few as one in 100,000 cells.  For an explanation of how PCR works, see

A major molecular response means that the amount of BCR-ABL protein in your marrow is very low.

A complete molecular response, formerly (and sometimes still) referred to as PCRU means that no BCR-ABL protein is detectible in the marrow utilizing the Polymerase Chain Reaction test.

Today, the use of "PCRU" as an indicator of deepest response is changing. With the increased sensitivity of PCR testing equipment, molecular responses are "graded" as MR3.5, MR4.0, and MR4.5. In the United States, a number of our labs are still not running at the International Scale (IS) sensitivity. In labs that are not testing at IS, the equipment is only able to detect up to a 3.5 log reduction. IS labs use equipment that is capable of higher sensitivities up to 4.0 and 4.5 log reductions. Thus if your tests have been done in a lab that is NOT International Scale and your next labs are in a International Scale lab, it is possible that you will be detectable at the higher sensitivities.

NOTE: Being found "undetectible" does not indicate cure as there is no way, even at the higher sensitivities, to know whether every cell in your body is free of the Philadelphia chromosome.