Researchers at the CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, the Ludwig Boltzmann Institute for Rare and Undiagnosed Diseases in Vienna, the University Medical Center of Regensburg, and the National Institute of Hematology and Infectious Diseases and the Semmelweis University in Budapest have studied the response to targeted leukemia therapy in unprecedented detail, using single-cell sequencing and epigenetic analysis. The paper published in the journal Nature Communications uncovers a precise molecular program in patients with chronic lymphocytic leukemia (CLL) who start treatment with the targeted cancer drug ibrutinib. While this program was shared by all patients, the speed of its execution differed widely. These results will help develop personalized strategies for managing CLL as a chronic disease, which is particularly relevant for CLL as a disease of the elderly.