PurposeNeoadjuvant CT-P6, a trastuzumab biosimilar, demonstrated equivalent efficacy to reference trastuzumab in a phase 3 trial of HER2-positive early-stage breast cancer (EBC) (NCT02162667). We report post hoc analyses evaluating pathological complete response (pCR) and breast pCR alongside additional efficacy and safety measures.MethodsFollowing neoadjuvant treatment and surgery, patients received adjuvant CT-P6 or trastuzumab (6 mg/kg) every 3 weeks for ≤ 1 year.ResultsIn total, 271 and 278 patients received CT-P6 and trastuzumab, respectively. pCR and breast pCR rates were comparable between treatment groups regardless of age, region, or clinical stage. Overall, 47.6% (CT-P6) and 52.2% (trastuzumab) of patients experienced study drug-related treatment-emergent adverse events (TEAEs), including 17 patients reporting heart failure (CT-P6: 10; trastuzumab: 7). Two CT-P6 and three trastuzumab patients discontinued adjuvant treatment due to TEAEs.ConclusionAdjuvant CT-P6 demonstrated comparable efficacy and safety to trastuzumab at 1 year in patients with HER2-positive EBC, supporting CT-P6 and trastuzumab comparability.Electronic supplementary materialThe online version of this article (10.1007/s00280-019-03920-4) contains supplementary material, which is available to authorized users.

510 Background: CT-P6 (C) is a proposed biosimilar to trastuzumab. This trial (NCT02162667) evaluated the similarity of C and trastuzumab in efficacy and safety for HER2+ EBC. Methods: 549 patients with HER2+ EBC were randomized to receive C (n=271) or trastuzumab (n=278) in combination with docetaxel (Cycles 1-4) and 5-fluorouracil, epirubicin, and cyclophosphamide (Cycles 5-8). C or trastuzumab was administered at 8 mg/kg (Cycle 1 only) followed by 6 mg/kg every 3 weeks. The primary endpoint was pathological complete response (pCR) rate at surgery. Secondary endpoints were overall response rate (ORR), PK, PD and safety. After surgery, patients received adjuvant C or trastuzumab to complete a total of 1-year treatment. Results: The pCR rate was 46.8% for C and 50.4% for trastuzumab. The 95% CIs for the risk ratio estimate were within the equivalence margin (0.74, 1.35) in PPS and ITT analyses. Other efficacy endpoints were similar between C and trastuzumab. The proportion of patients with at least 1 treatment-emergent SAE was 6.6% for C and 7.6% for trastuzumab. Only 1 patient in each group withdrew treatment due to significant LVEF decrease. Infusion-related reaction was reported for 8.5% of patients in C and 9.0% of patients in trastuzumab. Conclusions: This study demonstrated the similarity of efficacy in terms of pCR between CT-P6 and trastuzumab in EBC patients. Secondary efficacy endpoints also supported the similarity between CT-P6 and trastuzumab. CT-P6 was well tolerated with a similar safety profile to that of trastuzumab during the neoadjuvant period. Clinical trial information: NCT02162667. [Table: see text]

Purpose Equivalent efficacy was demonstrated for the biosimilar CT-P6 and trastuzumab following neoadjuvant therapy for patients with human epidermal growth factor receptor-2 (HER2)-positive early breast cancer. Following adjuvant treatment, efficacy and safety were comparable between treatments. We report updated safety and efficacy data after up to 3 years’ follow-up. Methods Following neoadjuvant chemotherapy with CT-P6/trastuzumab, patients underwent surgery and continued receiving adjuvant CT-P6/trastuzumab. The primary endpoint (previously reported) was pathological complete response. Time-to-event analyses (disease-free survival [DFS], progression-free survival [PFS], and overall survival [OS]), study drug-related and cardiac adverse events, and immunogenicity were assessed during post-treatment follow-up. Results Most patients entered the follow-up period (CT-P6: 259 [95.6%]; trastuzumab: 269 [96.8%]). After a median follow-up of 38.7 (CT-P6) and 39.6 (trastuzumab) months, medians were not reached for time-to-event parameters; estimated hazard ratios (HRs) and 3-year survival rates were similar between groups. Estimated HRs (95% confidence intervals) for CT-P6 versus trastuzumab were 1.23 (0.78–1.93) for DFS, 1.31 (0.86–2.01) for PFS, and 1.10 (0.57–2.13) for OS (intention-to-treat population). Safety findings were comparable between groups for the overall study and follow-up period, including study drug-related cardiac disorders (CT-P6: 22 [8.1%] patients; trastuzumab: 24 [8.6%] patients [overall]) and decreases in left ventricular ejection fraction. Immunogenicity was similar between groups. Conclusion The similarity of the time-to-event analyses between CT-P6 and trastuzumab supports the equivalence in terms of efficacy established for the primary endpoint. CT-P6 was well tolerated, with comparable safety and immunogenicity to trastuzumab. ClinicalTrials.gov: NCT02162667 (registered June 13, 2014)

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