HER2CLIMB-05

Background

Phase III randomized trial. N=654 (326 tucatinib, 328 placebo) with centrally confirmed HER2+ metastatic breast cancer without progression after first-line induction; no or asymptomatic brain metastases. Median age 54; 69.3% de novo MBC; 52.6% HR+.

Interventions and follow up

Arm A: Tucatinib 300mg twice daily + trastuzumab/pertuzumab
Arm B: Placebo + trastuzumab/pertuzumab
Primary endpoint: Progression-free survival (PFS)
mFollow up: 24.9mo (tucatinib) vs 16.3mo (placebo)

Results

PFS: 24.9 vs 16.3mo (8.6mo improvement), HR 0.641, 95% CI 0.514–0.799, P<.0001
Subgroups: benefit independent of brain metastasis status and hormone receptor status
OS: immature at this analysis

Adverse events

Gastrointestinal (tucatinib): diarrhea 72.7% (6.1% grade ≥3); nausea 33.1% (0.9% grade ≥3)
Hepatic (tucatinib): ALT elevation 28.2% (13.5% grade ≥3); AST elevation 25.8% (7.1% grade ≥3)
Discontinuation: 13.5% stopped tucatinib due to AEs

Conclusions

Adding tucatinib to dual HER2 blockade significantly improved PFS in first-line maintenance for HER2+ MBC (HR 0.641), with a manageable safety profile and no new safety signals. OS data remain immature.

Key Limitations

OS immature; relatively high toxicity discontinuation (13.5%); limited follow-up for long-term outcomes; excludes symptomatic brain metastases; clinical role evolving alongside competing first-line and maintenance regimens.

Clinical Context

Supports adding tucatinib to trastuzumab/pertuzumab as a potential first-line maintenance option in HER2+ MBC, expanding chemotherapy-free strategies. Complements other dual HER2 blockade approaches; positioning will be shaped by DESTINY-Breast09 and PATINA data. FDA review status pending.

References