The first head-to-head comparison of two BTK inhibitors was investigated in the ELEVATE-RR trial for relapsed/refractory CLL in which acalabrutinib demonstrated non-inferior PFS in comparison to ibrutinib (median 38 months in both arms), but there was a significantly lower incidence of atrial fibrillation with acalabrutinib (9 vs. 16%); among most frequent side effects, acalabrutinib also caused less hypertension, arthralgia, and diarrhoea but more headaches and cough. Here, BTK is linked to B-cell chronic lymphocytic leukemia.