Background: Neoadjuvant chemotherapy with dual HER2 blockade boosts pathologic complete response (pCR) rates in HER2+ breast cancer. The optimal chemotherapy backbone in this setting is unknown. We conducted a multicenter phase III trial to study whether anthracyclines would improve outcome compared to a carboplatin-taxane regimen (NCT01996267). Methods: We randomly assigned (1:1) patients with stage II-III HER2+ breast cancer to receive 9 cycles paclitaxel (80mg/m² day 1 and 8) and carboplatin (AUC = 6mg/ml·min) (arm A) or 3 cycles 5-fluoruoracil (500mg/m²), epirubicin (90mg/m²), and cyclophosphamide (500mg/m²) followed by 6 cycles paclitaxel and carboplatin (arm B). Both arms received trastuzumab (6mg/kg, loading dose 8mg/kg) and pertuzumab (420mg, loading dose 840mg) concurrent with all chemotherapy cycles, and cycles were repeated every 3 weeks. The primary endpoint was pCR in breast and axilla (ypT0/is,ypN0). Results: 438 patients were included and 418 (arm A 206 vs arm B 212) were evaluable for the primary endpoint. The pCR rate did not differ between arms (arm A 68% [95% CI 61-74] vs arm B 67% [95% CI 60-73], p = 0.75). Hormone receptor (HR) negative tumors had significantly higher pCR rates (87% vs 54%, p < 0.0001), but we found no evidence for treatment-by-HR interaction (p = 0.23). Common adverse events grade ≥3 were neutropenia (arm A 53% vs arm B 57%, p = 0.34), febrile neutropenia (arm A 2% vs arm B 11%, p = 0.0001), and diarrhea (arm A 17% vs arm B 12%, p = 0.14). Neuropathy grade ≥2 was common in both arms (arm A 31% vs arm B 29%, p = 0.83), while left ventricular ejection fraction (LVEF) decline grade ≥2 (defined as ≥10% decline from baseline or LVEF < 50%) was more common in arm B (arm A 18% vs arm B 29%, p = 0.007). Symptomatic left ventricular systolic dysfunction was rare ( < 1%) in both arms. Conclusions: Anthracyclines increase the incidence of febrile neutropenia and grade ≥2 LVEF decline, but do not improve pCR rate in the contemporary neoadjuvant treatment of HER2+ breast cancer with dual HER2 blockade. Therefore, we currently favor a carboplatin-taxane based regimen. Follow-up is required to confirm these results with regard to long-term outcome. Clinical trial information: NCT01996267