Background: Peg-Neutropine, GEMA BIOTECH SAU biosimilar Peg-Filgrastim, is the first Peg-Filgrastim approved in LATAM for prevention of febrile neutropenia in patients treated with myelosuppressive chemotherapy. Methods: Study population: women with stage 2, 3 or 4 of breast cancer scheduled to receive 4 or 6 cycles of chemotherapy (with Taxane) at 3 weeks interval. Stratification was based on breast cancer stage. Study drug was administered subcutaneously in a 6 mg dose. The study was blind to the assessors. The primary endpoint was Duration of Severe Neutropenia (DSN, Absolute Neutrophil Count-ANC < 500/mm3) in the first cycle of chemotherapy. Secondary endpoints were incidence of severe neutropenia (SN), other efficacy measures, and incidence of ADRs. The non-inferiority margin for DSN was estimated in less than 1 day. Results: A total of 120 subjects were randomized 1:1, 58 were treated with Peg-Neutropine and 62 with Peg-Filgrastim (Roche). Efficacy: SN was developed in 52/283 (18,4%) cycles with Peg-Neutropine in 27 patients and 48/297 (16,2%) cycles with Peg-Filgrastim (Roche) in 20 patients (p=0,4836). In the first cycle, 16 patients with Peg-Neutropine and 11 patients with Peg-Filgrastim (Roche) developed SN. In per protocol analysis mean DNS in the first cycle was 0,78 ± 1,53 days for Peg-Neutropine group and 0,53±1,25 for Peg-Filgrastim (Roche) group (95% IC for the difference -0,26; 0,76). Per ITT analysis the mean DSN was 0,90±1,79 for Peg- Neutropine group and 0,50±1,21 for Peg-Filgrastim (Roche) group, (95% IC for the difference -0,15; 0,95). For all the efficacy secondary endpoints the differences were not statistically significant. Safety: 7 ADRs were developed by 3 subjects with Peg-Neutropine and 31 ADRs were developed by 10 subjects with Peg-Filgrastim (Roche). The most common reaction was myalgia, and other ADRs were arthralgia, asthenia, bone pain and acid sensitive syndrome. Conclusions: Based on the non-inferiority margin established we conclude that Peg-Neutropine is biosimilar to Peg-Filgrastim (Roche). Clinical trial information: NCT03404752