Double-Blind, Randomized, Parallel Group, Phase Iii Study To Demonstrate Equivalent Efficacy And Comparable Safety Of Ct-P6 And Trastuzumab, Both In Combination With Paclitaxel, In Patients With Metastatic Breast Cancer (Mbc) As First-Line Treatment

629 Background: CT-P6(C) is an anti-HER2 MoAb, a biosimilar to trastuzumab (T). This trial is a global phase III study to compare C with T, both in combination with paclitaxel (P) as first-line treatment in women with HER2+ MBC. Methods: 475 patients with centrally confirmed HER2+ MBC were randomized to receive either C+P (n=244) or T+P (n=231). Patients had to have a baseline LVEF ≥50% and no history of serious cardiac disease. Study medication was as follows: C or T 8 mg/kg i.v. (day 1), followed by 3-weekly C or T 6 mg/kg. P (175 mg/m23-weekly) was co-administered. The primary endpoint was overall response rate (ORR) as determined by independent review. Pooled analysis with data from phase I/IIb (NCT01084863) and III studies (NCT01084876) was predefined and endorsed by the EMA. Patient safety was monitored throughout the study by an independent data monitoring committee. Treatment was continued until disease progression, death or patient’s withdrawal. Results: In the pooled ITT population, ORR was 57% for C+P and 62% for T+P (difference: 5%; 95% CI: -0.14, 0.04) during the first 8 cycles of treatment. The limits of the 95% CIs for the difference in the proportions of responders were contained within the pre-defined range [-0.15, 0.15] required for equivalence. Median time to progression and median time to response were 11.07 vs. 12.52 months (P =0.10), and 1.38 vs. 1.38 months (P =0.37) for C+P and T+P, respectively. Frequency of treatment-related AEs is shown in the Table. Conclusions: Equivalence of C and T was observed for ORR in patients with HER2+ MBC in combination with P as first-line therapy. Secondary efficacy endpoints also supported the comparability between C and T. C was well tolerated with a safety profile comparable to that of T. Clinical trial information: NCT01084876. [Table: see text]