e20593 Background: Pegfilgrastim (conjugate of filgrastim and 20 kDa polyethylene glycol (PEG) is approved for treatment of chemotherapy-associated neutropenia. BCD-017 (empegfilgrastim) is a covalent conjugate of filgrastim with 30 kDa PEG. Increased molecular weight of PEG molecule may provide additional benefits compared to pegfilgrastim. Methods: To compare efficacy and safety of filgrastim and BCD-017 at 3 mg and 6 mg doses an open-label, randomized, active-comparator, non-inferiority trial was conducted. 60 patients with histologically or cytologically confirmed breast cancer were randomly assigned to receive either subcutaneous (s.c.) injection of 3 mg BCD-017 (n=21), 6 mg BCD-017 (n = 20), or 5 mg/kg s.c. injections of filgrastim (n=19) administered daily until ANC ≥ 10x109 cells/L (maximum of 14 days) after chemotherapy (doxorubicin 60 mg/m2 and docetaxel 75 mg/m2) with stratification for weight and prior chemotherapy exposure. The primary efficacy endpoint was the incidence of severe neutropenia (ANC < 1.0x109 cells/L) during the first cycle of chemotherapy. Results: Incidence of severe neutropenia during the first chemotherapy cycle was 85,7%, 65,0% and 61,1% in BCD-017 3 mg, BCD-017 6 mg and filgrastim groups, respectively. Differences between BCD-017 groups and filgrastim group were not significant. Mean duration of grade 4 neutropenia in cycle 1 was 0,43, 0,40 and 0,33 days, accordingly (95% CI for difference between BCD-017 3 mg and filgrastim groups -0.22 to 0.41; 95% CI for difference between BCD-017 6 mg and filgrastim groups -0.25 to 0.38). Febrile neutropenia was observed only in BCD-017 3 mg and BCD-017 6 mg groups (one case in each group). A single administration of BCD-017 at the doses of 3 mg and 6 mg was as safe and well tolerated as standard daily filgrastim administration. There were no unexpected adverse events in all groups. Conclusions: The results of this study support comparable efficacy of single s.c. injection of 6 mg BCD-017 versus daily 5 mg/kg s.c. injections of filgrastim. Further phase III study of BCD-017 for treatment and prophylaxis of neutropenia in patients receiving chemotherapy is necessary. Clinical trial information: NCT01569087.