Real-world Outcomes of Dual HER2 Blockade Therapy in Metastatic HER2-Positive Breast Cancer: from Induction to Maintenance.

Background and objective: Dual human epidermal growth factor receptor 2 (HER2) blockade with trastuzumab and pertuzumab combined with taxane-based chemotherapy (Cht) has been the standard first-line treatment for HER2-positive metastatic breast cancer (mBC) for years, due to the impressive results of the CLEOPATRA study. Real-world (RW) studies have become critical for assessing treatment effectiveness and safety in real-life circumstances. The aim of this study was to analyze the treatment outcomes of first-line therapy for HER2-positive mBC in RW clinical practice, specifically focusing on the use of maintenance endocrine therapy (ET) in hormone receptor positive (HR-positive) patients.

Methods: This retrospective analysis included 106 HER2-positive mBC patients treated with trastuzumab and pertuzumab combined with taxane-based Cht from October 2015 to December 2020 at the University Hospital Centre Zagreb.

Results: At a median follow-up of 30 months, median progression-free survival (PFS) was 25 months for the total population (95% confidence interval [CI] 16 - not analyzed). Patients with de novo mBC had longer median PFS than patients with recurrent disease (not reached vs. 18 months; hazard ratio 1.99; 95% CI 0.69-3.64, p<0.022). Age, hormone receptor positivity, visceral involvement, number of Cht cycles and previous adjuvant trastuzumab did not impact PFS. Most HR-positive patients (N=55, 88.7%) received maintenance ET after induction Cht.

Conclusion: This retrospective study provides additional data on patient characteristics, treatment and outcomes of RW HER2-positive mBC patients treated with pertuzumab and trastuzumab as first-line therapy. In our institution, maintenance ET after induction Cht has become standard clinical practice.