SWOG S0221: a phase III trial comparing chemotherapy schedules in high-risk early-stage breast cancer

Abstract

Purpose: To determine the optimal dose and schedule of anthracycline and taxane administration as adjuvant therapy for early-stage breast cancer.

Patients and methods: A 2 × 2 factorial design was used to test two hypotheses: (1) that a novel continuous schedule of doxorubicin-cyclophosphamide was superior to six cycles of doxorubicin-cyclophosphamide once every 2 weeks and (2) that paclitaxel once per week was superior to six cycles of paclitaxel once every 2 weeks in patients with node-positive or high-risk node-negative early-stage breast cancer. With 3,250 patients, a disease-free survival (DFS) hazard ratio of 0.82 for each randomization could be detected with 90% power with two-sided α = .05. Overall survival (OS) was a secondary outcome.

Results: Interim analyses crossed the futility boundaries for demonstrating superiority of both once-per-week regimens and once-every-2-weeks regimens. After a median follow-up of 6 years, a significant interaction developed between the two randomization factors (DFS P = .024; OS P = .010) in the 2,716 patients randomly assigned in the original design, which precluded interpretation of the two factors separately. Comparing all four arms showed a significant difference in OS (P = .040) but not in DFS (P = .11), with all treatments given once every 2 weeks associated with the highest OS. This difference in OS seemed confined to patients with hormone receptor-negative/human epidermal growth factor receptor 2 (HER2) -negative tumors (P = .067), with no differences seen with hormone receptor-positive/HER2-negative (P = .90) or HER2-positive tumors (P = .40).

Conclusion: Patients achieved a similar DFS with any of these regimens. Subset analysis suggests the hypothesis that once-every-2-weeks dosing may be best for patients with hormone receptor-negative/HER2-negative tumors.

Fig 1.

CONSORT diagram for the original protocol of Southwest Oncology Group S0221 trial. AC, doxorubicin-cyclophosphamide; Q2 week, once every 2 weeks.

Fig 2.

(A) Kaplan-Meier disease-free survival plot for all randomly assigned patients by randomization arm. Number at risk at the beginning of each 12-month period is shown in the table. Three patients with no follow-up were excluded. (B) Kaplan-Meier overall survival plot of all randomly assigned patients by randomization arm. Three patients with no follow-up were excluded. (C) Kaplan-Meier disease-free survival plot by randomization arm for patients with triple-negative tumors (estrogen receptor negative, progesterone receptor negative, and human epidermal growth factor receptor 2 [HER2] negative). (D) Kaplan-Meier disease-free survival plot by randomization arm for patients with hormone receptor–positive (estrogen receptor–positive and progesterone receptor–positive) and HER2–negative tumors. 2wAC, doxorubicin-cyclophosphamide once every 2 weeks; AC + G, doxorubicin-cyclophosphamide with filgrastim; q 2 weeks, once every 2 weeks.