Minimal residual core binding factor AMLs by real time quantitative PCR--initial response to chemotherapy predicts event free survival and close monitoring of peripheral blood unravels the kinetics of relapse.

Minimal residual disease (MRD) was measured by RQ-PCR in 11 AML1/ETO and 13 CBFbeta/MYH11 patients at diagnosis, after induction chemotherapy, and at all subsequent visits. Median detection limits were 1:50,000 and 1:10,000, respectively. In 64/103 samples MRD was detectable and highly correlated in PB and BM. In 38/103 samples, where MRD was only detectable in BM, median BM MRD was 3.5log lower than at diagnosis. Event free survival was significantly inferior in case of <2log reduction post-induction MRD. Persistent MRD was always followed by hematological relapse. Molecular progression rate in relapsing CBFbeta/MYH11 was surprisingly slow with a time lag to hematological relapse approaching 1 year. This direct comparison between the two subgroups of CBF AMLs delineates clear biological differences and corroborates the value of RQ-PCR.