CLL-115: First Results of a Head-to-Head Trial of Acalabrutinib Versus Ibrutinib in Previously Treated Chronic Lymphocytic Leukemia

Context: Increased selectivity of the Bruton tyrosine kinase inhibitor (BTKi) acalabrutinib versus ibrutinib may improve tolerability. Objective: To compare acalabrutinib versus ibrutinib in patients with chronic lymphocytic leukemia (CLL). Design: Open-label, randomized, noninferiority, phase 3 trial. Patients: Previously treated CLL patients with del(17p) or del(11q) by central lab. Interventions: Oral acalabrutinib 100 mg twice daily (BID) or ibrutinib 420 mg once daily (QD) (stratified by del(17p) status, Eastern Cooperative Oncology Group performance status [2 vs ≤ 1], and number of prior therapies [1–3 vs ≥4]) until progression or unacceptable toxicity. Main Outcome Measures: Primary endpoint was progression-free survival (PFS), as assessed by independent review committee; secondary endpoints of all-grade atrial fibrillation (AF), grade ≥3 infection, Richter transformation, and overall survival (OS) were assessed in hierarchical order. Results: 533 patients (acalabrutinib, n=268; ibrutinib, n=265) were randomized (median age 66 years; median 2 prior therapies; del(17p) 45.2%; del(11q) 64.2%). At a median follow-up of 40.9 months (range 0.0–59.1), acalabrutinib was noninferior to ibrutinib with a median PFS of 38.4 months in both arms (HR: 1.00; 95% CI: 0.79–1.27). Acalabrutinib was statistically superior to ibrutinib in all-grade AF incidence (9.4% vs 16.0%; P=0.023). Among other secondary endpoints, incidences of grade ≥3 infection (acalabrutinib: 30.8%, ibrutinib: 30.0%) and Richter transformation (acalabrutinib: 3.8%, ibrutinib: 4.9%) were comparable between arms. Median OS was not reached in either arm (HR: 0.82; 95% CI: 0.59–1.15), with 63 (23.5%) deaths in the acalabrutinib arm and 73 (27.5%) in the ibrutinib arm. Among any-grade adverse events (AEs) in ≥20% of patients in either arm, acalabrutinib was associated with lower incidence of hypertension (9.4%, 23.2%), arthralgia (15.8%, 22.8%), and diarrhea (34.6%, 46.0%) but a higher incidence of headache (34.6%, 20.2%) and cough (28.9%, 21.3%). AEs led to treatment discontinuation in 14.7% of acalabrutinib- versus 21.3% of ibrutinib-treated patients. Any-grade AEs of clinical interest that were less frequent with acalabrutinib included cardiac (24.1% vs 30.0%), hypertension (above), and bleeding events (38.0% vs 51.3%). Conclusions: In this first head-to-head trial of BTKis in CLL, acalabrutinib demonstrated noninferior PFS with less cardiotoxicity and fewer discontinuations due to AEs versus ibrutinib.