Definition of the response to tyrosine kinase inhibitors as first-line treatment of chronic myeloid leukemia

The definitions are the same for patients in chronic phase, accelerated phase, and blast crisis and apply also to second-line treatment, when first-line treatment was changed for intolerance. The response can be assessed with either a molecular or a cytogenetic test, but both are recommended whenever possible. Cutoff values have been used to define the boundaries between optimal and warning, and between warning and failures. Because cutoff values are subjected to fluctuations, in case of cytogenetic or molecular data close to the indicated values, a repetition of the tests is recommended. After 12 months, if an MMR is achieved, the response can be assessed by real quantitative polymerase chain reaction (RQ-PCR) every three to six months, and cytogenetics is required only in case of failure or if standardized molecular testing is not available. Note that MMR (MR^3.0 or better) is optimal for survival, but that a deeper response is likely to be required for a successful discontinuation of treatment.