Amplification of the epidermal growth factor receptor 2 (HER2) gene occurs in 15-20% of breast cancers and was historically associated with poor prognosis. The CLEOPATRA trial established pertuzumab added to trastuzumab and chemotherapy as standard of care for metastatic HER2-positive breast cancer, demonstrating a 15.7-month improvement in median overall survival (OS). Strict trial inclusion criteria may limit generalizability to clinical practice. Population-based data can assess whether these survival benefits translate to real-world outcomes.
Women diagnosed with HER2-positive metastatic breast cancer in 2012-2021 were identified through the Cancer Registry of Norway and linked to health and treatment databases. Patients were categorized by treatment regimen and year of treatment initiation: pre-CLEOPATRA (2012-2014; trastuzumab ± chemotherapy) and post-CLEOPATRA (2015-2021; trastuzumab + pertuzumab ± chemotherapy). OS was estimated using Kaplan-Meier and Cox regression adjusted for clinical, and socioeconomic factors. Outcomes were benchmarked against CLEOPATRA.
The cohort comprised 329 women, 23% were aged ≥65 years. Seventy-eight patients (24%) received pre-CLEOPATRA regimens and 251 (76%) post-CLEOPATRA regimens; 59% met minimum one CLEOPATRA exclusion criterion. First-line dual HER2 blockade increased from 0% in 2012 to 75% in 2021. Median OS improved from 69 months to 96 months post-CLEOPATRA.
Four-year OS increased from 59% to 65% (adjusted hazard ratio 0.77, 95% CI 0.53-1.12). Real-world OS was consistent with CLEOPATRA outcomes. Nationwide real-world data demonstrate favorable survival outcomes following adoption of dual anti-HER2 therapy. While these findings are broadly consistent with the CLEOPATRA trial, the observational design does not allow direct assessment of equivalence between studies. all abbreviations in the abstract are standard in this field of research.
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