Comparative Effectiveness and Safety of Pertuzumab and Trastuzumab Plus Chemotherapy vs Trastuzumab Plus Chemotherapy for Treatment of Metastatic Breast Cancer.

IMPORTANCE: To date, limited studies have examined the comparative outcomes of pertuzumab treatment in the real-world setting. End-of-study analyses of the CLEOPATRA trial found median overall survival (OS) of 57.1 months in patients receiving pertuzumab compared with 40.8 months in control patients, a benefit of 16.3 months. However, studies examining the real-world use of pertuzumab have found conflicting results. OBJECTIVE: To assess the real-world comparative effectiveness and safety of pertuzumab, trastuzumab, and chemotherapy for patients with metastatic breast cancer in Ontario, Canada. DESIGN, SETTING, AND PARTICIPANTS: A population-based retrospective comparative effectiveness research study was conducted. Patients receiving first-line treatments for metastatic breast cancer from January 1, 2008, to March 31, 2018, in Ontario were identified. Data analysis was performed from November 13, 2019, to August 1, 2021. Thirteen patients had received treatment before diagnosis or were not Ontario residents and were excluded from the analysis. Of the remaining 1823 patients identified, 912 received pertuzumab and 911 were control patients. Using propensity-score methods, 579 pairs of patients receiving pertuzumab were matched to those in the control group, resulting in a total of 1158 patients in the final cohort. EXPOSURES: Patients in the case group received pertuzumab with trastuzumab and chemotherapy and those in the control group received trastuzumab and chemotherapy. MAIN OUTCOMES AND MEASURES: Overall survival (the primary outcome) and hazard ratios (HRs) were calculated using Kaplan-Meier and Cox proportional hazards regression methods. Secondary outcomes included cumulative incidence of safety end points including resource use and adverse events. Follow-up duration was up to 5 years from the start of therapy, with maximum follow-up to March 31, 2019. RESULTS: Of the 1158 matched patients (579 pairs) receiving pertuzumab and controls, 1151 (99%) were women (mean [SD] age, 58.2 [12.97] years). The median OS was higher in patients receiving pertuzumab (40.2; 95% CI, 35.6-47.8 months) than in the control patients (25.3; 95% CI, 22.8-27.6 months), a median OS improvement of 14.9 months. Pertuzumab was associated with reduced mortality (HR, 0.66; 95% CI, 0.57-0.79). The cumulative incidence of direct hospitalization at 1 year was lower among patients receiving pertuzumab (11.7%) compared with the control patients (19.0%) (P < .001). CONCLUSIONS AND RELEVANCE: Although the median OS in both the pertuzumab and control groups were shorter in this study than those observed in the CLEOPATRA trial, there appears to be a similar significant OS benefit with pertuzumab in the real-world setting.