Implications of detection of minimal residual disease

Complete remission can be achieved in the majority of children and adults with acute leukemia, but relapses are frequent due to persistent disease below the level of detectability of light microscopy. Recently, more sensitive molecular biologic and immunologic approaches have been developed for monitoring of leukemia-specific or -associated markers. Methods are now available for follow-up studies in all leukemic entities. New insights have already been gained into the efficiency of therapeutic strategies; persistence of a leukemic marker is a common finding in patients shortly after induction treatment and does not necessarily predict relapse, and increase of positive signals or reappearance of a leukemic marker in complete remission often precedes relapse. However, not all methods are standardized, and levels of sensitivity differ. Conclusions for stratification of postremission therapy can only be drawn after evaluation of ongoing, prospective studies.