AIM: This randomized, double-blind trial compared proposed biosimilar LA-EP2006 with reference pegfilgrastim in women receiving chemotherapy for breast cancer (PROTECT-1). PATIENTS & METHODS: Women (≥18 years) were randomized to receive LA-EP2006 (n = 159) or reference (n = 157) pegfilgrastim (Neulasta(®), Amgen) for ≤6 cycles of (neo)-adjuvant TAC chemotherapy. Primary end point was duration of severe neutropenia (DSN) during cycle 1 (number of consecutive days with absolute neutrophil count <0.5 × 10(9)/l) with equivalence confirmed if 90% and 95% CIs were within a ±1 day margin. RESULTS: For DSN, LA-EP2006 was equivalent to reference (difference: 0.07 days; 90% CI: -0.09-0.23; 95% CI: -0.12-0.26). CONCLUSION: LA-EP2006 and reference pegfilgrastim showed no clinically meaningful differences regarding efficacy and safety in breast cancer patients receiving chemotherapy.