MRD in AML: it is time to change the definition of remission

The possibility of defining residual disease far below the morphological level of 5% blast cells is changing the landscape of risk classification in acute myeloid leukemia (AML). The so-called minimal residual disease (MRD) approach at this time can establish the presence of leukemia cells down to levels of 1:1000-1:10(6) white blood cells, compared to 1:20 for morphology. Availability of the newer and more sensitive technology to quantify the level of leukemic burden raises the issue of whether MRD should emerge as a new definition of complete response. This paper explores some of the issues surrounding such a change in definition.