This is a prospective, open-label, randomized, phase III trial. Patients will be stratified after breast surgery, as per investigational site; menopausal status; node negative diagnosis, as per sentinel-node technique versus lymphadenectomy; hormone receptor status (positive versus negative).

Patients will be randomized to:

• Fluorouracil, doxorubicin, and cyclophosphamide (FAC) x 6 (cycles): 5-fluorouracil 500 mg/m2 + doxorubicin 50 mg/m2 + cyclophosphamide 500 mg/m2 day 1, every 3 weeks, for 6 cycles.
• FAC x 4 (cycles) → Paclitaxel x 8 (cycles): 5-fluorouracil 500 mg/m2 + doxorubicin 50 mg/m2 + cyclophosphamide 500 mg/m2 day 1, every 3 weeks, for 4 cycles, followed by 8 administrations of weekly paclitaxel 100 mg/m2

Premenopausal women with hormone receptor positive tumors must receive tamoxifen 20 mg daily for 5 years, after the end of chemotherapy.

Postmenopausal women with hormone receptor positive tumors are allowed to receive aromatase inhibitors as initial adjuvant hormone therapy or after tamoxifen.

All patients with breast conservative surgery must receive radiotherapy.

Estimated 5-year disease-free survival in the control arm (FAC x 6) is expected to be 80%. It is expected that disease-free survival will increase by 5% in the experimental arm (FAC-paclitaxel). 906 patients per arm must be recruited, to detect this difference with an alpha error of 0.05 and 80% power. Assuming a 6% post-randomization drop-out rate, 960 patients per arm are needed, 1920 in total.

Inclusion Criteria:

• Written informed consent.

• Histological diagnoses of operable invasive adenocarcinoma of the breast (T1-T3). Tumors must be Human Epidermal Growth Factor Receptor 2 (HER2) negative. Patients must be free of disease in the axilla (node negative). If lymphadenectomy is done, at least 10 nodes must be examined. If sentinel node technique is used, sentinel node must be free of disease. Patients must present at least one high risk criterion (St. Gallen, 1998) as follows:

  • Tumor size > 2 cm; and/or
  • ER and Progesterone Receptor (PgR) negative; and/or
  • Histological grade 2-3; and/or
  • Age < 35 years old.

• Time window between surgery and study randomization must be less than 60 days.

• Surgery must consist of mastectomy or conservative surgery. Margins free of disease and ductal carcinoma in situ (DCIS) are required. Lobular carcinoma is not considered a positive margin.

• Patients must not present evidence of metastatic disease.

• Status of hormone receptors in primary tumor. Results must be available before the end of adjuvant chemotherapy.

• Status of HER2 in primary tumor, known before randomization. Patients with Immunohistochemistry (IHC) 0 or +1 are eligible. For patients with IHC 2+, fluorescent in situ hybridization (FISH) is mandatory and result must be negative.

• Age >= 18 and <= 70 years old.

• Performance status (Karnofsky index) >= 80.

• Normal electrocardiogram (EKG) in the 12 weeks prior to randomization. If needed, normal cardiac function must be confirmed by left ventricular ejection fraction (LVEF).

• Laboratory results (within 14 days prior to randomization):

  • Hematology: neutrophils >= 1.5 x 10^9/l; platelets >= 100x 10^9/l; hemoglobin >= 10 mg/dl;
  • Hepatic function: total bilirubin <= 1 upper normal limit (UNL); Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) <= 2.5 UNL; alkaline phosphatase <= 2.5 UNL. If values of AST and ALT > 1.5 UNL are associated with alkaline phosphatase > 2.5 UNL, patient is not eligible.
  • Renal function: creatinine <= 175 mmol/l (2 mg/dl); creatinine clearance >= 60 ml/min.

• Complete stage workup during the 12 weeks prior to randomization (mammograms are allowed within a 20 week time window). All patients must have a bilateral mammogram, thorax x-ray, abdominal echography and/or computed tomography (CT)-scan. If bone pain, and/or alkaline phosphatase elevation, a bone scintigraphy is mandatory. This test is recommended for all patients. Other tests, as clinically indicated.

• Patients able to comply with treatment and study follow-up.

• Negative pregnancy test done in the 14 previous days to randomization.

Exclusion Criteria:

• Prior systemic therapy for breast cancer.
• Prior therapy with anthracyclines or taxanes (paclitaxel or docetaxel) for any malignancy.
• Prior radiotherapy for breast cancer.
• Bilateral invasive breast cancer.
• Pregnant or lactating women. Adequate contraceptive methods must be used during chemotherapy and hormone therapy treatments. Negative pregnancy test in the 14 previous days to randomization.
• Any T4 or N1-3 or M1 tumor.
• HER2 positive breast cancer (IHC 3+ or positive FISH result).
• Pre-existing grade >=2 motor or sensorial neurotoxicity by the National Cancer Institute Common Toxicity Criteria (NCICTC) v-2.0.
• Any other serious medical pathology, such as congestive heart failure, unstable angina, history of myocardial infarction during the previous year, uncontrolled hypertension or high risk arrhythmias.
• History of neurological or psychiatric disorders, which could preclude the patients to free informed consent.
• Active uncontrolled infection.
• Active peptic ulcer; unstable diabetes mellitus.
• Previous or current history of neoplasms different from breast cancer, except for skin carcinoma, cervical in situ carcinoma, or any other tumor curatively treated and without recurrence in the last 10 years; ductal in situ carcinoma in the same breast; lobular in situ carcinoma.
• Concomitant treatment with other investigational products. Participation in other clinical trials with a non-marketed drug in the 20 previous days before randomization.
• Concomitant treatment with other therapy for cancer.
• Males.