Minimal residual disease in chronic lymphocytic leukemia: A still current issue in 2018

Minimal residual disease (MRD) is widely used in oncohematology. In chronic lymphocytic leukemia (CLL), it can be measured by flow cytometry or polymerase chain reaction and is getting a greater place, owing to the dramatic therapeutic advances in the management this disease. As MRD decrease after chemoimmunotherapy is associated with improved progression free and overall survivals, its measure is now recommended as a surrogate marker for cytotoxic drugs licensures. This association is independent from treatment received and raises a few questions, such as sequential MRD measures to stop treatment in case of an early deep response and on the opposite, treatment continuation until reaching undetectable MRD (with the possible use of maintenance therapy). Furthermore, following MRD after a cytotoxic treatment could lead clinical trials investigators to propose pre-emptive treatments in case of MRD re-growth, to avoid overt relaspe. MRD re-growth kinetics and CD4 count after treatment completion can improve MRD-based survival predictions. On the other hand, BCR inhibitors do not lead to undetectable MRD, but their association with chemoimmunotherapy increases the proportion of patients reaching that goal. Moreover, BCL2 inhibitors do lead to deep response including in the relapse/refractory setting, giving to MRD a central place in currently investigated treatments evaluation.