Open-Label, Phase 1 Study to Evaluate Duration of Severe Neutropenia After Same-Day Dosing of Eflapegrastim in Patients With Breast-Cancer

Inclusion Criteria: * Willing and capable of giving written Informed Consent and able to adhere to study drug dosing time and blood draw schedules * New diagnosis of histologically confirmed early-stage breast cancer (ESBC), defined as operable Stage I to Stage IIIA breast cancer * Candidate to receive adjuvant or neoadjuvant TC chemotherapy * Age must be at least 18 years for the Early Phase, and between 18 to ≤55 years for the Expansion Phase * ANC ≥1.5×10\^9/liter (L). * Platelet count ≥100×10\^9/liter (L). * Hemoglobin \>10 grams per deciliter (g/dL). * Calculated creatinine clearance \>50 milliliter per minute (mL/min). * Total bilirubin ≤1.5 milligrams per deciliter (mg/dL). * Aspartate aminotransferase (AST)/serum glutamic oxaloacetic transaminase (SGOT) and alanine aminotransferase (ALT)/serum glutamic pyruvic transaminase (SGPT) ≤2.5×upper limit of normal (ULN). * Alkaline phosphatase ≤2.0×ULN. * Eastern Cooperative Oncology Group (ECOG) ≤2 * Willing to practice 2 forms of contraceptives (1 must be a barrier method), from study entry through 30 days after last dose of study drug/ early discontinuation * Negative urine pregnancy test within 30 days before randomization Exclusion Criteria: * Active concurrent malignancy (except non melanoma skin cancer or carcinoma in situ of the cervix) or life-threatening disease * Known sensitivity to Escherichia coli (E. coli) derived products * Concurrent adjuvant cancer therapy other than the trial-specified therapies * Locally recurrent/metastatic breast cancer * Previous exposure to filgrastim, pegfilgrastim, or other G-CSF products in clinical development within 3 months prior to the administration of study drug * Receiving anti-infectives, has an underlying medical condition or other serious illness that would impair the ability to receive protocol-specified treatment * Used any investigational drugs, biologics, or devices within 30 days prior to study treatment or plans to use any of these during the course of the study * Prior bone marrow or stem cell transplant * Prior radiation therapy within 30 days prior to enrollment * Major surgery within 30 days prior to enrollment * Pregnant or breastfeeding