Importance of Minimal Residual Disease in the Era of Targeted Therapies in Chronic Lymphocytic Leukemia.

Background: The level of minimal residual disease (MRD), often binarized into detectable or undetectable MRD according to certain thresholds, is strongly associated with long-term outcomes after chemo- and chemoimmunotherapy.

Summary: Driven by our improved understanding of the biology of chronic lymphocytic leukemia (CLL), the recent decade has shown a shift from chemotherapy-based regimens to regimens based on targeted agents that exploit distinct biological vulnerabilities of CLL. These targeted agents can be broadly classified into inhibitors of Bruton tyrosine kinase (BTK) and BCL2 as well as CD20-directed antibodies. Depending on which agent and which combination of agents is used, the levels or status of MRD can have varying clinical relevance. This has implications on the prognosis after therapy as well as on possible strategies to guide treatment duration and intensity.

Key messages: This review summarizes the main discoveries related to MRD in the context of targeted therapies. Furthermore, it provides an overview on current hurdles and caveats related to the implementation of MRD in regular clinical care and summarize open research questions that need to be addressed with future clinical studies.