Clinical confirmation to demonstrate similarity for a biosimilar pegfilgrastim: a 3-way randomized equivalence study for a proposed biosimilar pegfilgrastim versus US-licensed and EU-approved reference products in breast cancer patients receiving myelosuppressive chemotherapy

Female patients ≥ 18 years of age with Stage IIA, IIB or IIIA breast cancer, who were suitable and intended to undergo adjuvant treatment with TAC (docetaxel, doxorubicin, cyclophosphamide) chemotherapy were eligible for this study. Inclusion criteria included: patients within 60 days of complete surgical resection of the primary breast tumor, either lumpectomy or mastectomy, with sentinel lymph node biopsy or axillary dissection, with clear margins for both invasive and ductal carcinoma in situ (DCIS); Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2; ANC ≥ 1.5 × 10⁹/L; platelet count ≥ 100 × 10⁹/L; adequate renal function (serum creatinine < 1.5 × upper limit of normal [ULN]) and hepatic function (bilirubin < ULN, transaminases and alkaline phosphatase [AP] < 1.5 × ULN); normal cardiac function evidenced by a left ventricle ejection fraction (LVEF) ≥ 55%; no evidence of metastatic disease; and baseline bilateral mammography or other scan to exclude cancer on the contralateral breast. Patients were excluded if they had or received any of the following: (concomitant or prior) except in situ lesion, either ductal or lobular, of the contralateral breast; prior chemotherapy (either adjuvant or neoadjuvant) for this incidence of breast cancer; history of uncontrolled cardiac disease; immunotherapy, hormonal therapy (e.g., tamoxifen or aromatase inhibitors), or Herceptin^® (trastuzumab) concurrently or within 30 days of screening; concurrent radiation therapy; investigational therapy concurrently or within 30 days of screening; peripheral neuropathy > Grade 1; major organ allograft or condition requiring chronic immunosuppression; or history of other malignancy within the last 5 years (except cured basal cell carcinoma of skin, carcinoma in situ of uterine cervix, or DCIS).

This was a confirmatory, randomized, controlled, assessor-blinded, multicenter study comparing efficacy and safety of the proposed pegfilgrastim biosimilar to the US-licensed pegfilgrastim reference product and the EU-approved pegfilgrastim reference product conducted in 11 Central and Eastern European countries. The study consisted of three phases: a screening period ≤ 3 weeks; an 18-week active treatment period including 6, 3-week cycles of TAC chemotherapy (docetaxel 75 mg/m², doxorubicin 50 mg/m², and cyclophosphamide 500 mg/m²); and a safety follow-up period ≤ 30 weeks following the completion of the TAC regimen. Eligible patients were randomized to either the proposed pegfilgrastim biosimilar (APO-Peg), US-licensed pegfilgrastim reference product (US-Neulasta^®) or EU-approved pegfilgrastim reference product (EU-Neulasta^®) in a 2:1:1 ratio. Premedication with dexamethasone and ondansetron was initiated before administration of each chemotherapy cycle. Each patient received 6 doses of pegfilgrastim (6 mg/0.6 mL pre-filled syringe for each) for each chemotherapy cycle, administered as subcutaneous injection on Day 2 of each cycle (at least 24 h after chemotherapy).

In Cycle 1, blood samples were collected for complete blood counts with differentials on Day 0, 1, 3, 5, 6, 7, and every day until ANC recovery post-nadir to ≥ 2.0 × 10⁹/L, or up to Day 15 if recovery did not occur earlier. Blood samples for ANC measurements in Cycles 2–6 were collected mainly to assess safety. Blood samples were collected during the screening, treatment, and follow-up periods for immunogenicity testing.

The primary efficacy endpoint was the duration of severe neutropenia (DSN), defined as ANC below 0.5 × 10⁹/L. Secondary endpoints included: depth and peak of ANC nadir in Cycle 1; time to the ANC recovery post-nadir in Cycle 1; rates of FN (defined as a single temperature ≥ 38.3 °C or temperature ≥ 38.0 °C for over 1 h and ANC less than 0.5 × 10⁹/L or less than 1 × 10⁹/L and predicted decline to ≤ 0.5 × 10⁹/L over the next 48 h) by cycle and across all cycles. Safety assessment included: the incidence of adverse events (AEs) classified by system organ class, preferred term, severity, and relationship to study medication; injection site reactions; vital signs; presence of antibodies to pegfilgrastim; and abnormal clinical laboratory results.

The inference for equivalence was based on the two-sided 95% confidence interval (CI) for the difference in means between the proposed pegfilgrastim biosimilar and the US-licensed or EU-approved pegfilgrastim reference product for DSN in Cycle 1 (in days). Equivalence was defined as a CI range of [− 0.5 days, + 0.5 days]. The two-sided 95% CIs were derived from a one-way ANOVA model accounting for the treatment effect. For statistical analyses, treatment groups were defined as follows:

Full analysis set (FAS)-As Randomized included all enrolled subjects who were randomized, received at least one dose of active treatment, and who had any follow-up data for the primary endpoint variables. Treatment assignment for subjects was based on the treatment they were randomized to (As Randomized allocation). FAS-As Randomized represents the prespecified primary analysis set used for efficacy endpoints.

A total of 595 patients were randomized from 56 investigational centers in 11 countries. All subjects were suitable for neoadjuvant TAC treatment (all chemotherapy naïve subjects: 41.8% Stage IIa; 27.7% Stage 27.7%; and 30.6% Stage IIIa). Patient demographics and breast cancer history were consistent across the treatment arms (Table 1). Of those randomized, 589 patients were dosed, with 547 (92.9%) completing 6 cycles of treatment and 42 (7.1%) discontinuing the study (Fig. 1). Some subjects who withdrew from the treatment phase were followed in the safety follow-up phase.

As a sensitive measure of efficacy [10], the assessment of DSN in Cycle 1 (versus subsequent cycles) was chosen as the primary endpoint. Overall, the mean DSN in Cycle 1 is comparable across treatments and essentially the same between the FAS As Treated and As Randomized populations (Table 2). For the As Randomized population, the 95% CI of the difference in mean DSN in Cycle 1 between the proposed pegfilgrastim biosimilar and US-licensed pegfilgrastim reference product was slightly outside the equivalence margin, but for the proposed pegfilgrastim biosimilar and EU-approved pegfilgrastim reference product was contained within the pre-defined margin (Table 2). Given that sampling of ANC for determination of DSN in a clinical setting is conducted on a daily basis, as in this study, the breach of 0.01 days, which equates to approximately 14.4 min from the upper limit of the equivalence range (0.51 days), is not considered clinically significant. The results for the As Treated population showed a 95% CI within the equivalence range for the proposed pegfilgrastim biosimilar between both the US-licensed and EU-approved pegfilgrastim reference products, confirming similar efficacy (Table 2).

Similarity between the proposed pegfilgrastim biosimilar and the EU-approved and US-licensed reference products was also supported by comparative results between all treatment arms for all secondary efficacy endpoints (Table 3 and data not shown). The rate of FN (As Randomized) was similar between treatment arms with the highest incidence occurring in Cycle 1 (as expected) and decreasing in subsequent treatment cycles (Table 3). In addition, the mean ANC values showed similar results among the three treatment arms [overall mean peak ANC of 28.9 × 10⁹/L (day 3.1–3.4); overall mean ANC nadir of 0.5 × 10⁹/L (day 7.1–7.3), and recovery of ANC (≥ 2.0 × 10⁹/L; day 9.2–9.5)] (Table 4).

The number of AEs in the three treatment arms were similar, and the majority were considered to be mild to moderate in severity (Table 5). For this analysis, any subject receiving the proposed biosimilar in any cycle (regardless of randomization) was included in the APO-Peg arm. Out of 589 subjects across the treatment arms, 539 (91.5%) reported at least one AE in the treatment phase (89.7% in the APO-Peg arm; 94.8% in the US-Neulasta arm; 92.8% in the EU-Neulasta arm; Table 5).

Two of the most common AEs were neutropenia in (52.8% of subjects overall; 51.4% in the APO-Peg arm; 58.5% in the US-Neulasta arm; 50.4% in the EU-Neulasta arm) and nausea (47.0% of subjects overall; 44.1% in the APO-Peg arm; 49.6% in the US-Neulasta arm; 52.0% in the EU-Neulasta arm) (Table 5). In addition, bone pain, a common event associated with pegfilgrastim [12] thought to be directly related to treatment with filgrastim, occurred at a similar frequency in the three treatment groups (45.3% in the APO-Peg arm; 52.6% in the US-Neulasta arm; 56.0% in the EU-Neulasta arm; Table 5) and none of these events were reported as a serious adverse event (SAE), or led to subject withdrawal.

One subject randomized to US-licensed pegfilgrastim reference product but receiving the proposed pegfilgrastim biosimilar died due to disease progression. Five additional life-threatening events were reported in the APO-Peg treatment arm (3 FN, 1 pancytopenia, and 1 pulmonary embolism). None of these events were related to the study drug. The incidence of immunogenicity was low and similar across treatment arms, including no apparent clinically meaningful effects associated with anti-drug antibodies (ADAs) or neutralizing antibodies (data not shown).