The SWOG S0221 randomized phase III trial is evaluating two distinct doxorubicin/cyclophosphamide (AC) dosing schedules—continuous versus dose-dense biweekly—each followed by paclitaxel administered either every two weeks or weekly for 12 weeks, as post-operative adjuvant chemotherapy in node-positive or high-risk node-negative breast cancer. The trial is currently active but no longer enrolling.
The SWOG Cancer Research Network's S0221 trial is a randomized phase III investigation comparing the efficacy of two AC-based adjuvant chemotherapy regimens in patients who have undergone surgical resection for stage I, II, or III breast cancer with node-positive or high-risk node-negative disease. The central question is whether a continuous AC schedule or a biweekly dose-dense AC schedule, each followed by paclitaxel, yields superior oncologic outcomes in this population.
Following the AC induction component, participants receive paclitaxel via one of two delivery schedules: every two weeks or weekly for 12 weeks. This factorial design allows assessment of both the AC dosing interval and the paclitaxel administration frequency as independent variables. Pegfilgrastim is incorporated as granulocyte colony-stimulating factor support, reflecting standard practice for dose-dense regimens to mitigate febrile neutropenia risk.
The trial encompasses a broad receptor-defined population, including HER2-positive, estrogen receptor-positive, estrogen receptor-negative, progesterone receptor-positive, and progesterone receptor-negative subtypes, as well as male breast cancer cases. This heterogeneity may complicate subgroup interpretation but also enhances the generalizability of findings across the adjuvant breast cancer landscape. The study is currently active but closed to new enrollment, with results anticipated to inform optimal sequencing and scheduling of anthracycline-taxane adjuvant regimens.
Key points
- Randomized phase III design comparing continuous versus biweekly dose-dense AC followed by paclitaxel (biweekly or weekly ×12) as adjuvant therapy after breast cancer resection
- Eligible population includes node-positive and high-risk node-negative stage I–III breast cancer across all major receptor subtypes
- Pegfilgrastim is used as prophylactic G-CSF support within dose-dense arms
- Trial is active but no longer recruiting; conducted under the SWOG Cancer Research Network
- Findings are expected to clarify whether AC dosing schedule or paclitaxel frequency differentially impacts outcomes in resected breast cancer
Why it matters
Optimizing the scheduling of anthracycline-taxane adjuvant regimens remains a clinically relevant question, as dosing intensity and interval directly affect both efficacy and tolerability in the post-operative breast cancer setting. S0221 results could refine standard-of-care sequencing decisions for oncologists managing high-risk early-stage disease.