190P - 3-year follow-up of a phase III trial comparing the efficacy and safety of neoadjuvant and adjuvant trastuzumab and its biosimilar CT-P6 in HER2 positive early breast cancer (EBC)

Abstract

BackgroundCT-P6 was approved by both US FDA and European Commission as a biosimilar to reference trastuzumab (RTZ). Here we report updated long term efficacy and safety. Methods549 patients with HER2 positive EBC were randomized 1:1 to CT-P6 (n=271) or RTZ (n=278) with docetaxel (Cycles 1-4) and 5-fluorouracil, epirubicin and cyclophosphamide (Cycles 5-8). After surgery, patients received CT-P6 or RTZ monotherapy to complete a total of 1 year and were followed up to 3 years from enrollment of the last patient. Stratified Cox regression and Kaplan-Meier methods were used for time to event (TTE) analyses. Results528 patients (259 in CT-P6 and 269 in RTZ) were followed up. The median duration of follow-up was 39 months. Overall, the rates of disease-free survival (DFS) and overall survival (OS) were similar between CT-P6 and RTZ in both PPS and ITT set. The number of DFS events (42 [16.3%] in CT-P6 and 36 [13.8%] in RTZ) and OS events (18 [6.6%] in CT-P6 and 18 [6.5%] in RTZ) were comparable in ITT set. Median DFS and OS have not been reached due to an insufficient number of events. The mean LVEF was more than 60% in both groups, and no new cases of heart failure were reported during the follow-up period. Table. Summary of Long Term Efficacy Endpoints.Table190PTablePPSITT setCT-P6 n=248RTZ n=256CT-P6 n=258RTZ n=261DFS rate1 year (95% CI)0.95 (0.91 – 0.97)0.96 (0.93 – 0.98)0.95 (0.91 – 0.97)0.96 (0.93 – 0.98)2 years (95% CI)0.87 (0.81 – 0.90)0.89 (0.85 – 0.92)0.87 (0.82 – 0.90)0.89 (0.85 – 0.93)3 years (95% CI)0.82 (0.77 – 0.87)0.82 (0.75 – 0.88)0.83 (0.77 – 0.87)0.83 (0.76 – 0.88)Hazard ratio (95% CI)1.23 (0.78 – 1.94)1.23 (0.78 – 1.93)p-value0.38080.3807CT-P6 n=248RTZ n=256CT-P6 n=271RTZ n=278OS rate1 year (95% CI)1.00 (1.00 – 1.00)1.00 (0.97 – 1.00)0.99 (0.97 – 1.00)0.99 (0.97 – 1.00)2 years (95% CI)0.98 (0.95 – 0.99)0.98 (0.96 – 0.99)0.97 (0.93 – 0.98)0.98 (0.96 – 0.99)3 years (95% CI)0.95 (0.91 – 0.97)0.94 (0.90 – 0.96)0.93 (0.90 – 0.96)0.94 (0.90 – 0.96)Hazard ratio (95% CI)0.87 (0.42 – 1.82)1.10 (0.57 – 2.13)p-value0.71810.7710 ConclusionsDFS and OS rates and cardiotoxicity at a median follow-up of 39 months support the similarity of CT-P6 and reference trastuzumab in early-stage breast cancer. Clinical trial identificationNCT02162667. Legal entity responsible for the studyCelltrion. FundingCelltrion. DisclosureJ. Stebbing: Officer / Board of Directors, Editer-in-Chief: Oncogene; Advisory / Consultancy: Celltrion; Advisory / Consultancy: Vor Biopharma; Advisory / Consultancy: Benevolent AI; Officer / Board of Directors: BB Biotech Healthcare Trust; Officer / Board of Directors: Xerion Healthcare. Y. Baranau: Honoraria (self), Travel / Accommodation / Expenses: Roche; Honoraria (self), Travel / Accommodation / Expenses: Pfizer; Travel / Accommodation / Expenses: Novatis. V. Moiseyenko: Speaker Bureau / Expert testimony: AstraZeneca. J. Pikiel: Travel / Accommodation / Expenses: Roche. A. Eniu: Research grant / Funding (self): AstraZeneca; Research grant / Funding (self): Celltrion; Research grant / Funding (self): Pfizer. S.J. Lee: Leadership role, Shareholder / Stockholder / Stock options, Full / Part-time employment, Stock option: Celltrion. M.J. Kim: Full / Part-time employment: Celltrion. S. Kim: Full / Part-time employment: Celltrion. S. Park: Full / Part-time employment: Celltrion. J.H. Bae: Full / Part-time employment: Celltrion. F.J. Esteva: Advisory / Consultancy: Celltrion; Advisory / Consultancy: Roche; Advisory / Consultancy: Novartis; Advisory / Consultancy: Pfizer. All other authors have declared no conflicts of interest.