RecruitingPhase 2Drug trialClonal Dynamics of Chronic Lymphocytic Leukaemia Treated With Pirtobrutinib After Previous Treatment With ZanubrutinibThis is a multicentre single-arm prospective phase II trial evaluating pirtobrutinib in the treatment of relapsed/refractory (R/R) Chronic Lymphocytic Leukaemia (CLL) patients who have previously received zanubrutinib, and to specifically evaluate Bruton Tyrosine Kinase (BTK) mutational status (clonal dynamics) before, during and after treatment with pirtobrutinib.