Background. Using a 2 × 2 factorial design, we compared the efficacy of two different schedules of chemotherapy (CT), dose-dense (DD) every 2 weeks versus standard duration every 3 weeks and the role of Fluorouracil (F) in addition to EC, in the adjuvant treatment of node positive BC pts. Patients and Methods. Node positive early BC pts younger than 70 years were eligible and randomly assigned to one of the following treatment arms: ARM A (4 courses of EC [90/600 mg/m2, on day 1, q 21] followed by 4 courses of T [175 mg/m2 on day 1, q 21]); ARM B (4 courses of FEC [600/90/600 mg/m2, on day 1, q 21] followed by 4 courses of T [175 mg/m2 on day 1, q 21]); ARM C (4 courses of EC [90/600 mg/m2, on day 1, q 14] followed by 4 courses of T [175 mg/m2 on day 1, q 14]); ARM D (4 courses of FEC [600/90/600 mg/m2, on day 1, q 14] followed by 4 courses of T [175 mg/m2 on day 1, q 14]). Pts enrolled in the DD arms (ARM C and D) received subcutaneous pegfilgrastim (6 mg) 24 hours after CT. HER2-positive pts enrolled after April 2006 received trastuzumab for 1 year at the end of CT. The primary study endpoint was disease free survival (DFS). Secondary endpoints included overall survival (OS) and toxicity. All analyses were conducted according to the intention-to-treat principle. Results. From April 2003 to July 2006, 2091 pts were enrolled (545 in ARM A, 544 in ARM B, 502 in ARM C, 500 in ARM D). The planned number of CT cycles was completed in 89% of pts in the DD group and in 88.1% of pts in the standard duration group. Pts treated with DD CT (ARM C + ARM D) experienced more frequently anemia (all grades: 67.2% vs 49.5%, p < .0001; G3-G4: 0.2% vs 1.4%, p = .004) and bone pain (53.5% vs 39.2%, p < .0001). Neutropenia occurred more frequently in standard duration arms (ARM A + ARM B): 66.7% vs 28.0%, p = < .0001. At a median follow up of 7.0 years, multivariate analysis, showed that DD treatments (ARM C + ARM D vs ARM A + ARM B) improved the primary endpoint, DFS (hazard ratio [HR] = 0.78; 95% CI 0.66-0.94; p = .007), and OS (HR = 0.68; 95% CI 0.52-0.87; p = .002). Conversely, the addition of F to EC did not improve clinical outcomes: the HR for DFS and OS (ARM A + ARM C vs ARM B + ARM D) were respectively 0.98 (95% CI 0.83-1.17; p = .85) and 0.93 (95% CI 0.73-1.19; p = .578). Subgroup analyses revealed that the benefits associated with DD CT were independent of hormone receptor status: in hormone receptor positive the HRs for DFS and OS were 0.80 (0.65-0.98) and 0.69 (0.51-0.93) respectively; in hormone receptor negative the HRs for DFS and OS were 0.67 (0.47-0.95) and 0.57 (0.36-0.92) respectively (p for interaction for DFS: 0.339; p for interaction for OS: 0.495). Pathological tumor size, nodal status (1-3 vs ≥ 4 positive nodes), histological grade and hormone receptor status were independently associate with DFS and OS. Conclusions. DD CT as adjuvant treatment in node positive BC pts, improves DFS and OS significantly. Conversely, the addition of F to EC does not improve clinical outcomes. (ClinicalTrials.gov number, NCT00433420). Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S5-06.