Six-year survival outcomes for patients with HER2-positive early breast cancer treated with CT-P6 or reference trastuzumab: observational follow-up study of a phase 3 randomised controlled trial

Background: The Phase 3 CT-P6 3.2 study demonstrated equivalent efficacy and comparable safety between CT-P6 and reference trastuzumab in patients with human epidermal growth factor receptor-2 (HER2)-positive early breast cancer after up to 3 years’ follow-up. 

Objective: To investigate long-term survival with CT-P6 and reference trastuzumab. 

Methods: In the CT-P6 3.2 study, patients with HER2-positive early breast cancer were randomised to neoadjuvant chemotherapy with CT-P6 or reference trastuzumab, surgery, and adjuvant CT-P6 or reference trastuzumab before a 3-year post-treatment follow-up. Patients who completed the study could enter a 3-year extension (CT-P6 4.2 study). Data were collected every 6 months to assess overall survival (OS), disease-free survival (DFS), and progression-free survival (PFS). 

Results: Of 549 patients enrolled in the CT-P6 3.2 study, 216 (39.3%) patients continued in the CT-P6 4.2 study (CT-P6, 107; reference trastuzumab, 109) (intention-to-treat extension set). Median follow-up was 76.4 months for both groups. Medians were not reached for time-to-event parameters; estimated hazard ratios (95% confidence intervals) for CT-P6 versus reference trastuzumab were 0.59 (0.17–2.02) for OS, 1.07 (0.50–2.32) for DFS, and 1.08 (0.50–2.34) for PFS. Corresponding 6-year survival rates in the CT-P6 and reference trastuzumab groups, respectively, were 0.96 (0.90–0.99) and 0.94 (0.87–0.97), 0.87 (0.78–0.92) and 0.89 (0.81–0.94), and 0.87 (0.78–0.92) and 0.89 (0.82–0.94). 

Conclusions: Data from this extended follow-up of the CT-P6 3.2 study demonstrate the comparable long-term efficacy of CT-P6 and reference trastuzumab up to 6 years. 

EudraCT number: 2019-003518-15 (retrospectively registered 10 March 2020).