Impact of Pegfilgrastim on Trastuzumab Anti-tumor Effect and ADCC in Operable HER2+ Breast Cancer Breast Cancer

Inclusion Criteria: * Female patients aged ≥ 18 years at time of inform consent signature. * Histologically proven HER2 positive breast cancer defined as 3+ staining intensity by immunohistochemistry (IHC) or a 2+ IHC staining intensity and HER2 gene amplification by FISH.Note: HER2 status will be determined as per institutional practice. * Operable breast tumor with tumor size and staging: \> 20 mm, cN0 or cN1, M0 before any AC or FEC chemotherapy, and at least one measurable lesion ≥10 mm in longest diameter at inclusion according to RECIST 1.1. * No radiological sign of disease progression at time of randomisation. * Patient previously treated by 4 cycles of AC or 3 to 4 cycles of FEC without febrile neutropenia and without prior pegfilgrastim treatment. * Availability of a representative formalin-fixed paraffin-embedded (FFPE) tumor specimen from initial diagnosis (i.e. an archival paraffin block is preferred; or at least 20 unstained slides) with its histological report. * Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 * Adequate organ function as defined by the following lab tests (to be carried out within 7 days prior C1D1):Bone marrow (Absolute neutrophil count ≥ 1.5 x 109/L, Platelet count \> 100 x 109/L, (without transfusion within 21 days prior to C1D1), Hemoglobin value ≥ 9 g/dL), Renal function (Calculated creatinine clearance by MDRD or CKD-EPI \>50 mL/min/1.73m2 or serum creatinine \< 1.5ULN), Liver function (Alanine aminotransferase (ALT) an…