1 Introduction
As the most common cancer in women and the second most common cancer overall, more than 2 million new cases of breast cancer were reported worldwide in 2018 [
1]. Approximately 20% of patients with breast cancer have human epidermal growth factor receptor 2 (HER2) overexpression [
2‐
4], resulting in aggressive tumor cell growth, poor prognosis, unresponsiveness (to common therapies), and shorter survival [
5,
6].
Trastuzumab (Herceptin
®, Genentech/Roche, Inc.), a humanized monoclonal antibody targeting the extracellular domain of HER2, in combination with chemotherapy has greatly improved the treatment of metastatic HER2-positive breast cancer compared with chemotherapy alone (overall response rate [ORR] 50 vs. 32%) [
7‐
9]. It is currently approved for the treatment of early, advanced breast cancer and metastatic gastric and gastroesophageal junction adenocarcinoma with HER2 overexpression or
HER2 gene amplification [
10]. However, the high cost of trastuzumab limits treatment access for many eligible patients [
11].
Biosimilars are biologic medicines with no clinically meaningful differences in safety or efficacy compared with approved reference products and can potentially increase patient access [
12]. Several trastuzumab biosimilars have been approved by the European Medicines Agency (EMA), the U.S. Food and Drug Administration (FDA), and/or the China National Medical Products Administration (NMPA), including HLX02 (Zercepac
®, Henlius Biotech, Inc.), approved by both the EMA and the NMPA [
13‐
15].
A biosimilar must demonstrate similarity to the reference product stepwise, starting with analytical and nonclinical comparisons of quality characteristics and biological activity, including toxicity [
16,
17]. HLX02 is the first China-manufactured, globally evaluated trastuzumab biosimilar, and the amino acid sequence is identical to that of trastuzumab. Structural, functional, and preclinical similarities between HLX02 and trastuzumab have been demonstrated both in vitro and in vivo [
18]. A phase I study in healthy Chinese male volunteers demonstrated the equivalent safety, tolerability, and pharmacokinetics of HLX02 and China- and EU-sourced trastuzumab (NCT02581748) [
19,
20]. This study was designed to assess the clinical similarity of HLX02 and reference trastuzumab for the treatment of recurrent or metastatic HER2-positive breast cancer. The safety, tolerability, and immunogenicity of HLX02 and reference trastuzumab were monitored throughout the study.
2 Methods
2.1 Study Design and Participants
This randomized, multicenter, double-blind phase III equivalence study was designed to compare the efficacy and safety of HLX02 with reference trastuzumab in adult patients with HER2-positive recurrent or metastatic breast cancer. Patients were recruited from 89 centers in China, the Philippines, Poland, and Ukraine (Table 1 in the Electronic Supplementary Material [ESM]).
Eligible patients were aged ≥ 18 years, had histologically or cytologically confirmed breast adenocarcinoma, and an Eastern Cooperative Oncology Group (ECOG) performance status score of 0–1. Other key inclusion criteria were HER2 positivity (defined as fluorescence in situ hybridization amplification ratio ≥ 2 or immunohistochemistry score 3+), known estrogen-receptor (ER) and progesterone-receptor (PgR) status at study entry, measurable disease assessed by central imaging review (CIR), normal (within institutional range of normal) left ventricular ejection fraction (LVEF), and adequate hematologic, hepatic, and renal function. Key exclusion criteria were previously or on-treated (with systemic chemotherapy, biological, or targeted agent, or any other anticancer agent except hormonal therapy) metastatic breast cancer, symptomatic or untreated brain metastasis or any other central nervous system metastases, uncontrolled systemic disease that in the investigator’s opinion made the administration of study drug hazardous, prior exposure to doxorubicin (> 360 mg/m2 or equivalent), and residual nonhematologic grade 2 or higher toxicity from prior therapies. Full inclusion and exclusion criteria are listed in Table 2 in the ESM.
The study protocol was reviewed and approved by the relevant independent ethics review board at each study site. All patients provided written informed consent before inclusion. This trial was conducted in accordance with the principles outlined in the Declaration of Helsinki, good clinical practice guidelines, and all applicable local regulatory requirements. Study design details are illustrated in Fig. 1 in the ESM.
2.2 Randomization and Masking
After confirmation of eligibility, patients were randomized 1:1 to receive either HLX02 or EU-trastuzumab in combination with docetaxel. Randomization was conducted using a block randomization scheme and stratified by ER/PgR status, prior neo-/adjuvant therapy with trastuzumab, and ethnicity. An interactive web response system was used to assign patients to study groups as per a predefined randomization code. Randomization codes were not revealed to study participants, investigators, or study site personnel until all final clinical data had been entered into the database and the database had been locked and released for analysis. ORR and other outcomes were also assessed by blinded reviewers.
2.3 Treatments
The study consisted of a 28-day screening period and a treatment period. In the treatment period, patients received HLX02 or EU-trastuzumab at an initial dose of 8 mg/kg over 90-min intravenous infusion on day 1, cycle 1, followed by 6 mg/kg study drugs once every 3 weeks for a maximum of 12 months. Docetaxel 75 mg/m2 was administered over 60-min intravenous infusion on day 2 of cycle 1 and then 60 min after the infusion of HLX02 or EU-trastuzumab in the following cycles at the investigator’s discretion for a maximum of 12 months. Infusions were administered in line with site-specific protocols, local guidelines, and product information for reference trastuzumab.
2.4 Endpoints and Assessments
The primary efficacy endpoint of this study was ORR up to week 24 (ORR24), defined as the proportion of patients with a best response of complete response (CR) or partial response (PR) from the first assessment up to week 24. Secondary efficacy endpoints included ORR at weeks 6, 12, 18, and 24; disease control rate (DCR; the proportion of patients who achieved CR, PR, or stable disease [SD] for ≥ 12 weeks); clinical benefit rate (CBR; the proportion of patients who achieved CR, PR, or durable SD [SD sustained for ≥ 24 weeks]); duration of response (DoR); 12-month progression-free survival (PFS) rate; and 12-, 24-, and 36-month overall survival (OS) rate. Tumor response was evaluated based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 by blinded CIR until week 24, after which it was evaluated by the principal investigator. Tumor assessments were performed at screening, weeks 6, 12, 18, and 24, and then every 9 weeks with computed tomography (CT) scan or magnetic resonance imaging (MRI). The method used was consistent throughout the entire study. Bone scans or X-rays and brain CT scan/MRI were performed at screening and during the treatment period if clinically indicated.
The safety and tolerability of HLX02 or EU-trastuzumab were evaluated in this study by recording the incidence, severity, and causality of treatment-emergent adverse events (TEAEs), serious TEAEs, serious adverse events (SAEs) and adverse events (AEs) of special interest (AESIs). TEAEs were defined as AEs that began or worsened in severity during or following the first administration of study medication and ≤ 30 days (± 2) following the last dose of study medication. As the most common safety issue with trastuzumab, cardiac function was monitored by echocardiogram (ECG) or multigated acquisition scan at screening (within 42 days before randomization) and after every 3 cycles (or more frequently if clinically indicated). Patients who permanently discontinued the study drug because of a drop in LVEF (for a persistent [> 8 weeks] decline of LVEF or for suspension of HLX02/trastuzumab dosing on more than three occasions for cardiomyopathy [
21]) continued to undergo assessments until the LVEF values returned to ≥ 50%.
All AEs, physical examinations, vital signs, ECGs, and laboratory tests were graded according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.03 and classified according to the Medical Dictionary for Regulatory Activities (MedDRA) version 21.1. Cardiac AEs were collected up to 12 months after randomization, in line with LVEF calculations. Routine laboratory tests were performed by the local laboratory at screening, during treatment, at the end of the study, and 30 days after the end of the last administration.
Pharmacokinetic blood samples were collected from all patients at cycle 1 (within 7 days prior to infusion) and every 3 cycles starting at cycle 3 (cycles 3, 6, 9, 12, and 15). Extended pharmacokinetic collections were collected from all patients in cycle 1 (at the end of infusion) and cycles 4 (prior to infusion) and 8 (prior to and after infusion). Immunogenicity (as assessed by antidrug antibody [ADA] and neutralizing ADA [NADA]) was evaluated with ADA and NADA at screening, cycles 3, 6, 9, 12, 15, and at the safety follow-up visit. The samples were submitted to the central laboratory (WuXi AppTec bioanalytical services department, Shanghai, China) and measured using validated assays.
2.5 Statistical Analysis
Assuming a 5% dropout rate, a sample size of 608 was required to ensure that 578 patients (289 in each group) randomly received treatments to evaluate the equivalence between HLX02 and EU-trastuzumab with approximately 84% power. Equivalence was defined as the 95% confidence interval (CI) for the treatment difference being fully contained in the margins of ± 13.5%. These margins were derived by reviewing historical data from two randomized studies of trastuzumab in patients with HER2-positive metastatic breast cancer [
8,
10] and estimated with the Der Simonian–Laird [
22] random effect.
The intention-to-treat (ITT) set was defined as all patients randomly allocated to study drug, regardless of whether a dose of study drug was given. The per-protocol (PP) set comprised all patients who received ≥ 8 cycles of treatment and had one or more tumor assessment after treatment, or who discontinued treatment early because of disease progression or intolerable toxicity without major protocol deviations. The safety set included all patients who were randomly allocated and received at least one dose of study drug (HLX02 or EU-trastuzumab). The pharmacokinetic set comprised all patients who received study drug and had at least one measured concentration at a scheduled pharmacokinetic time point with no protocol deviations or other pharmacokinetics-affecting events.
The ITT and PP population sets were used for efficacy analyses. Per ITT set, patients with missing ORR assessments were regarded as nonresponders in the primary analysis. The difference (95% CI) in ORR24 between the treatment groups was assessed for statistical significance with a chi-squared test. Sensitivity analyses of ORR between the two treatment groups (HLX02 and EU-trastuzumab) were conducted using a stratified Cochran–Mantel–Haenszel (CMH) test (95% Wald CI). The stratification factors for CMH tests were ER/PgR status, prior neo-/adjuvant therapy with EU-trastuzumab, and ethnicity. The CMH test used for the primary efficacy analysis was repeated for the PP set.
For the secondary efficacy endpoints, ORR, CBR, and DCR were analyzed using the same method as for the primary efficacy endpoint. Other secondary efficacy endpoints, such as DoR; PFS up to 12 months; OS rate at 12, 24, and 36 months; and OS at the cut-off date in the two treatment groups were presented graphically using Kaplan–Meier curves along with a summary of associated statistics (i.e., the probability of being event free) and the corresponding two-sided 95% CIs. Furthermore, the treatment difference, which was characterized by the “HLX02/EU-trastuzumab” hazard ratio (HR), was calculated using a stratified Cox proportional hazards model with ER/PgR status, prior (neo)/adjuvant therapy with trastuzumab, and ethnicity as covariates.
All analyses, summaries, and listings were calculated using SAS® software (version 9.4 or later, SAS Institute Inc., Cary, NC, USA). This study and all data were monitored by an independent monitoring committee.
4 Discussion
This randomized, multicenter, double-blind phase III trial demonstrated the therapeutic equivalence between HLX02 and reference trastuzumab in patients with recurrent or metastatic breast cancer based on 95% CIs of the intergroup difference of ORR24 in relation to the prespecified equivalence margins (± 13.5%). There were no statistically significant differences in all efficacy endpoints, pharmacokinetics, safety, or immunogenicity between the treatment groups.
Trastuzumab was initially approved for the treatment of metastatic HER2-positive breast cancer [
7,
23]. Several established equivalence studies of trastuzumab biosimilars, including MYL-1401O [
24] (Biocon/Mylan), BCD-022 (BIOCAD) [
25], and PF-05280014 (Pfizer) [
26], were conducted in patients with metastatic breast cancer. Based on the recent findings of a systematic literature review presented at the 2018 European Society for Medical Oncology congress, both early-stage and metastatic breast cancer are appropriate for the equivalence evaluation of trastuzumab biosimilar drugs to trastuzumab [
27]. The efficacy and safety similarity evaluations of HLX02 to trastuzumab were conducted in patients with metastatic breast cancer in this study.
Even though trastuzumab in combination with pertuzumab and chemotherapy is the current standard treatment for HER2-positive breast cancer in many countries [
28], trastuzumab, as the first effective therapeutic monoclonal antibody, which revolutionized the treatment of HER2-positive breast cancer [
29], remains a fundamental treatment option. To assess the similarity between HLX02 and trastuzumab through between-group ORR comparisons, pertuzumab was not included in the treatment regimen in this study. Another reason for not including pertuzumab is its lack of accessibility worldwide.
The therapeutic equivalence of HLX02 to trastuzumab was statistically demonstrated by the primary efficacy results in both the ITT (
p = 0.983, risk difference in ORR − 0.1%) and the PP sets (
p = 0.727, risk difference in ORR 1%). Even through the secondary efficacy analyses results of DoR, PFS, and OS were in favor of HLX02 at some time points according to Fig.
2, no statistically significant differences were observed between the two treatment groups in the ITT and PP sets based on the 1-year results.
The ORR at week 24 (59.3%), median DoR (10.6 months), PFS (11.7 months), and OS (not reached) observed in the HLX02 treatment group in this study were comparable to those observed in patients with metastatic breast cancer treated with trastuzumab in the reference study: ORR at week 24 64%; median DoR 11.1 months; median PFS 11.1 months; median OS not estimable [
24]. Sensitivity analyses of primary and secondary efficacy endpoints were performed in the following subgroups: ER/PgR status, prior neo-/adjuvant therapy with trastuzumab, and ethnicity (Asian and non-Asian). Results were consistent with the primary efficacy analysis and supported the conclusion of therapeutic equivalence. Long-term follow-up is important to accurately assess the efficacy outcomes. Efficacy parameters, including DoR and PFS, were followed up to 12 months. OS was estimated up to 12, 24, and 36 months. Long-term OS results will be reported once available.
The primary endpoint ORR is a sensitive endpoint for identifying the differences between a biosimilar candidate and the reference drug through direct measurement of drug activity [
16,
17]. The equivalence margins of this study were derived by reviewing the historical ORR of chemotherapy plus trastuzumab and estimating with the Der Simonian–Laird estimate effect model [
8,
10]. The intergroup difference in ORR was estimated as 0.2493 (95% CI 0.1579 to 0.3407). To increase assay sensitivity, the margins were defined as ± 13.5%, which was tighter than the lower boundary of the estimated 95% CI. The margins selected for this study were consistent with other phase III equivalence studies of approved trastuzumab biosimilars, including the above-mentioned MYL-1401O [
24] and PF-05280014 [
26,
30], as well as CT-P6 (Celltrion) [
31,
32], ABP980 (Amgen/Allergan) [
33], and SB3 (Samsung Bioepis) [
34].
There were no notable differences between the two treatment groups regarding the type, incidence, or severity of TEAEs. This study also showed that the safety profiles were comparable with the known safety profiles of trastuzumab in patients with breast cancer [
21,
24]. Clinical laboratory evaluations, vital signs, physical examinations, immunogenicity, and other safety observation (ECG, ECOG) results were similar between the two treatment groups. ADAs were detected overall in two patients in each treatment group, indicating similar immunogenicity between HLX02 and reference trastuzumab. The low immunogenic potential was consistent with published data for trastuzumab and trastuzumab biosimilars [
24,
26].
Trastuzumab has been reported as related to increased risks of cardiac toxicity [
7]. Thus, cardiac disorders in the HLX02 and trastuzumab treatment groups were carefully assessed. The frequency of cardiac disorders was low and similar between the two groups (three vs. six patients). Two patients in the HLX02 group (one case each of left ventricular dysfunction and pericardial effusion) and three patients in the EU-trastuzumab group (one case each of congestive cardiac failure, coronary artery disease, and ventricular arrhythmia) experienced a cardiac disorder that resulted in drug interruption or withdrawal. Two patients in the HLX02 group and three patients in the EU-trastuzumab group had a serious cardiac disorder related to study medication. The cardiac disorders reported in this study were similar to those previously reported [
21,
26].
Overall, the safety findings in the current trial were consistent with those expected of trastuzumab and previous studies of trastuzumab biosimilars [
10,
24,
26]. A long-term extension study that further monitors the efficacy and safety of HLX02 is under consideration.
Acknowledgements
The authors thank all the participants and families who were involved in the HLX02 phase III study, the clinical study teams (Clinical Operation: Haoyu Yu, Yue Li; Medical R&D: Ying Li; Statistics: Jiancheng Cheng, Boyao Shan; Medical writing: Chen Hu), and Katherine Chai, Xin Zhang, Alvin Luk, Weidong Jiang, Scott Liu, Ling Li, and Wenjie Zhang of Shanghai Henlius Biotech, Inc., for providing support for the study.