Background
ALPINE was a phase III randomized open-label head-to-head trial comparing zanubrutinib (a highly selective second-generation BTK inhibitor) versus ibrutinib (first-generation BTK inhibitor) in relapsed/refractory CLL or SLL. Ibrutinib had been the foundational BTKi and CLL standard of care since 2014 but is associated with off-target toxicities (atrial fibrillation, hypertension, bleeding, arthralgias) from inhibition of non-BTK kinases. ALPINE was designed to determine whether zanubrutinib's improved BTK selectivity would translate into superior efficacy and/or safety.
Interventions and follow up
Arm A: Ibrutinib 420 mg PO once daily until progression (n=325)
Arm B: Zanubrutinib 160 mg PO BID until progression (n=327)
Primary endpoint: ORR per investigator (non-inferiority then superiority); key secondary: PFS, OS, safety
mFollow up: 29.6 months
Arm B: Zanubrutinib 160 mg PO BID until progression (n=327)
Primary endpoint: ORR per investigator (non-inferiority then superiority); key secondary: PFS, OS, safety
mFollow up: 29.6 months
Results
ORR: 80.4% (zanubrutinib) vs 72.9% (ibrutinib), P=.0264 (zanubrutinib superior)
2-yr PFS: 78.4% vs 65.9%, HR 0.65, 95% CI 0.49–0.86, P=.0024
del17p/TP53-mutant 24-mo PFS: 72.6% vs 54.6%
OS: HR 0.76, P=.10 (not significant, data immature)
Atrial fibrillation/flutter (all grades): 5.2% vs 13.3%, P<.001
2-yr PFS: 78.4% vs 65.9%, HR 0.65, 95% CI 0.49–0.86, P=.0024
del17p/TP53-mutant 24-mo PFS: 72.6% vs 54.6%
OS: HR 0.76, P=.10 (not significant, data immature)
Atrial fibrillation/flutter (all grades): 5.2% vs 13.3%, P<.001
Adverse events
Cardiovascular: atrial fibrillation Grade ≥3 2.5% vs 4.0%; hypertension Grade ≥3 14.5% vs 12.6%
Hematologic/infectious (Grade ≥3, zanubrutinib vs ibrutinib): neutropenia 28.4% vs 21.7%; infections 22.2% vs 26.5%
Other: overall Grade ≥3 AEs 67.3% vs 70.4%; bleeding (all grades) 42.5% vs 43.7%; diarrhea Grade ≥3 ~1% both arms
Hematologic/infectious (Grade ≥3, zanubrutinib vs ibrutinib): neutropenia 28.4% vs 21.7%; infections 22.2% vs 26.5%
Other: overall Grade ≥3 AEs 67.3% vs 70.4%; bleeding (all grades) 42.5% vs 43.7%; diarrhea Grade ≥3 ~1% both arms
Conclusions
Zanubrutinib demonstrated superior ORR and significantly improved 2-year PFS (HR 0.65) versus ibrutinib in R/R CLL/SLL, with significantly less atrial fibrillation (5% vs 13%), establishing zanubrutinib as a preferred BTKi in R/R CLL based on both superior efficacy and improved cardiac safety over first-generation ibrutinib.
Key Limitations
Open-label design (IRC-confirmed responses mitigate some bias); OS not yet mature; no venetoclax-based comparator arm; no head-to-head with acalabrutinib in CLL (ASPEN was in Waldenstrom); patients with prior BTKi exposure excluded; efficacy difference (HR 0.65) likely reflects both higher BTK occupancy with twice-daily dosing and better tolerability (fewer discontinuations); hypertension rates similar to ibrutinib, so cardiovascular monitoring still required; BTK C481 resistance mutations remain relevant for both covalent BTKi, with non-covalent BTKi (pirtobrutinib) representing the next-generation alternative.
Clinical Context
ALPINE led to FDA approval of zanubrutinib for CLL/SLL in January 2023, providing the first head-to-head BTKi comparison in CLL showing superiority over ibrutinib. ESMO and iwCLL guidance favor next-generation BTKi over ibrutinib for both 1L and R/R CLL. The significantly lower AF rate (5% vs 13%) is clinically meaningful in the older CLL population with high baseline cardiovascular comorbidity. In the BTKi-refractory setting, pirtobrutinib (BRUIN, Lancet 2023) and venetoclax-based salvage are key emerging strategies. The choice between continuous BTKi and fixed-duration venetoclax combinations (AMPLIFY) continues to shape optimal CLL sequencing in both frontline and relapsed settings.