BTK and B-cell chronic lymphocytic leukemia: Therefore, the resistance to ibrutinib in this model likely resembles the mechanism of the first group of patients, which is not linked to mutations in BTK and PLCG2. Even though this concerns only a small group of patients (6–7% of ibrutinib-treated CLL patients, and 13–30% of ibrutinib resistant cases)44,45, there is a high clinical need for these patients.