Abstract P2-14-12: Eflapegrastim, a Novel Long-Acting Granulocyte-Colony Stimulating Factor: Integrated Safety Results in Patients with Early-Stage Breast Cancer Treated with TC Chemotherapy

Abstract Background: Eflapegrastim (E) represents the first myeloid growth factor innovation in more than 15 years. A novel, long-acting recombinant human granulocyte-colony stimulating factor (rhG-CSF), E consists of a rhG-CSF analog conjugated to a human IgG4 Fc fragment via a polyethylene glycol linker. Preclinical and Phase I and II pharmacodynamic and pharmacokinetic data showed increased potency for E versus pegfilgrastim (P). Two independent randomized Phase III trials comparing fixed dose E and P (E 3.6 mg G-CSF and P 6.0 mg G-CSF) for the management of chemotherapy-induced neutropenia (CIN) have recently been completed. Both trials met the primary endpoint of non-inferiority for E vs P in Cycle 1 duration of severe neutropenia (P Patients and Methods: Patients with early-stage breast cancer (ESBC) who were candidates for adjuvant or neoadjuvant chemotherapy were randomized 1:1 in two open-label Phase III trials to E 13.2 mg (3.6 mg G-CSF) or standard P (6 mg G-CSF) administered on Day 2 following TC (docetaxel/cyclophosphamide) chemotherapy on Day 1 of each of 4 cycles. Blood for CBC and serum chemistry was collected in every cycle. Safety assessments began with the first dose of TC and continued for one year after the last dose of study drug. AEs and laboratory values were graded according to NCI CTCAE version 4.03. Immunogenicity was assessed from blood samples collected on Day 1 of each cycle, at the end-of-treatment visit, and at 6- and 12-month follow-up visits. Results: A total of 660 patients who received at least one dose of eflapegrastim (n=334) or pegfilgrastim (n=326) were included in this integrated safety analysis. The two treatment groups were well balanced for demographics and baseline disease characteristics. The mean age was 59y, ~40% were aged >65y, ~54% weighed >75kg, and ~80% were treated in the adjuvant setting. Median relative dose intensity for T and C was >99% for both groups. A similar percentage of patients in both treatment groups discontinued treatment due to AEs (4% E vs 6% P), with 2% in each group discontinuing due to AEs related to E or P. Serious AEs were similar in both groups (15% each). Incidence of AEs irrespective of causality were also similar between groups (74% E vs. 72% P). No notable differences between groups were observed in the types of study-drug-related AEs. The majority of study-drug-related AEs occurred with an incidence ≤10% for both E and P. As expected with myeloid growth factors, study-drug-related AEs occurring in >10% in either group were bone pain (E vs P: 33% vs 34%), arthralgia (15% vs 10%), back pain (14% vs 9%), myalgia (14% vs 9%), and headache (11% vs 8%). Incidence of febrile neutropenia and neutropenic complications were similar and less than 5% in each treatment group. No leukocytosis, splenic rupture, or anaphylaxis was reported in any patient receiving E or P. The overall incidence of immunogenicity was similar in both groups and there was no demonstrable impact on clinical safety or efficacy. Conclusions: Two large, randomized Phase III trials (Total n=660) of E vs P administered once-per-cycle showed E at a lower G-CSF dose to be safe and effective for the prophylaxis of CIN in patients with ESBC receiving TC chemotherapy. E is a novel long-acting rhG-CSF with increased potency and similar toxicity to P and may provide an attractive alternative for growth factor support of patients at high risk for CIN-related complications. Citation Format: Lee S Schwartzberg, Gajanan Bhat, Julio Peguero, Richy Agajanian, Jayaram Bharadwaj, Alvaro Restrepo, Osama Hlalah, Inderjit Mehmi, Shanta Chawla, Francois Lebel, Patrick W Cobb. Eflapegrastim, a novel long-acting granulocyte-colony stimulating factor: Integrated safety results in patients with early-stage breast cancer treated with TC chemotherapy [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-14-12.