Abstract GS2-07: PHARE randomized trial final results comparing 6 to 12 months of trastuzumab in adjuvant early breast cancer

Since 2005, 12 months of trastuzumab added to chemotherapy alone is the standard of care in patients with HER2-positive breast cancer. PHARE (9Protocol for Herceptin® as Adjuvant therapy with Reduced Exposure9) is the first trial comparing a reduction of adjuvant trastuzumab versus the standard 12 months. In 2012, the first analysis failed to prove that 6-months was non-inferior to 12-months of adjuvant trastuzumab (NCT00381901). The current presentation reports the final analysis. Methods: The trial was sponsored by the French National Cancer Institute (INCa) (www.e-cancer.fr), and approved by central Ethical Committee on May 15 th 2006. Patients with HER2-positive early breast cancer were randomly assigned between 12 and 6 months of adjuvant trastuzumab duration. The randomization was stratified by concomitant or sequential trastuzumab administration with chemotherapy, estrogen receptor (ER) status and center. The primary objective was non-inferiority of 6- versus 12-months arms in the intent to treat population, in terms of disease-free survival (DFS) with a pre-specified hazard margin of 1.15. Overall Survival (OS) and metastasis free survival (MFS) were secondary endpoints. Results: A total of 3380 patients were randomized, their median age was 54 years (21-86). Patients and disease characteristics were well balanced between the two arms. No involved axillary node was observed in 54.5% of cases, 41.7% of tumors were ER negative. At a median follow-up of 7.5 years, 704 events counting for DFS were observed. Between the 12- and 6-months arms, the adjusted Hazard Ratio (HR) for DFS rates was 1.08 (95%CI: 0.93-1.25; p=0.39) favoring the longer exposure. The 1.15 margin of non-inferiority was included in the 95%CI. No heterogeneity in terms of treatment effect was observed, no significant difference for trastuzumab duration effects was found in any subgroups.For OS and MFS, the adjusted HR were 1.13 (95%CI 0.92-1.39) and 1.15 (95%CI 0.96-1.37), respectively. Conclusion: The choice of the non-inferiority margin will remain inherently a subject of controversy especially in the context of oncology trials where the primary outcome is survival and the least additional death could be considered unacceptable questioning the very feasibility of such trials. Nevertheless, PHARE failed to show that 6 months of adjuvant trastuzumab was non-inferior to 12 months. The standard of care should remain 12 months of adjuvant trastuzumab. Citation Format: Pivot X, Romieu G, Debled M, Pierga J-Y, Kerbrat P, Bachelot T, Espie M, Lortholary A, Fumoleau P, Serin D, Jacquin J-P, Jouannaud C, Rios M, Abadie-Lacourtoisie S, Venat-Bouvet L, Cany L, Catala S, Khayat D, Gambotti L, Pauporte I, Faure Mercier C, Paget-Bailly S, Henriques J, Grouin J-M. PHARE randomized trial final results comparing 6 to 12 months of trastuzumab in adjuvant early breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS2-07.