Clinical importance of speed of response to therapy in childhood lymphoblastic leukaemia

Speed of response to therapy predicts outcome in childhood lymphoblastic le ukaemia. This observation has been made studying both blood and bone marrow in children on widely differing treatment regimens from the 1970s to the p resent day. It appears to be independent of other classical prognostic fact ors such as age and diagnostic white cell count. Currently some major colla borative groups are using the rate of initial disease clearance to risk-str atify subsequent therapy and this practice may increase. The best way to measure the rate of disease clearance remains to be defined . Watching disappearance of peripheral blood blasts is the least invasive m ethod but possibly the least sensitive. Molecular quantitation of minimal r esidual disease (MRD) after achievement of conventional remission is much m ore sensitive but less specific. It cannot be applied to all patients and i s costly and time consuming. The degree of marrow infiltration remaining af ter 7 or 14 days may fall between the two but is often difficult to estimat e reliably and reproducibly due to technical limitations. The three techniq ues may reflect response to therapy in a way slightly different from each o ther and may not be direct correlates. The best compromise may be to use al l three but to reserve MRD study only for those who clear their blood and b one marrow after 7 days.