What question did this study set out to answer?

To determine if adding adjuvant chemotherapy to ovarian function suppression and endocrine therapy improves breast cancer outcomes.

May 30, 2026

A phase III trial evaluating addition of adjuvant chemotherapy to ovarian function suppression + endocrine therapy in premenopausal women with pN0-1, HR+/HER2– breast cancer and Oncotype recurrence score ≤ 25 (OFSET): NRG-BR009.

Key Points

To determine if adding adjuvant chemotherapy to ovarian function suppression and endocrine therapy improves breast cancer outcomes.
Phase III randomized trial comparing OFS+ET to ACT+OFS+ET, enrolling premenopausal women with early-stage HR+/HER2– tumors.
Patients are stratified by nodal and recurrence score status, with a total expected enrollment of 3,960.
Primary endpoint is invasive breast cancer-free survival, analyzed for 380 events post-surgery.
Estimated 5-year invasive breast cancer-free survival of 92.3% for pN1 patients on ACT+OFS+ET.
Estimated 5-year invasive breast cancer-free survival of ~95% for pN0 patients on ACT arm.
Power analysis suggests a minimum effect size with a hazard ratio of 0.75 is possible with sufficient event accrual.

Abstract

TPS650 Background: The TAILORx and RxPONDER trials showed that recurrence score (RS) identifies many postmenopausal pts who do not benefit from addition of ACT to endocrine therapy (ET); however, RS also identifies subsets who do benefit (node-neg/high clinical risk/RS 16-20, node-neg/RS 21-25, and node-pos/RS ≤25). Most premenopausal pts in these trials did not receive ovarian function suppression (OFS) as part of their ET regimen. Given the observed benefit from OFS in high-risk premenopausal pts with HR+/HER2– BC in SOFT/TEXT, we question whether the ACT benefit in TAILORx/RxPONDER was due to chemotherapy-induced OFS. To address this, we developed OFSET, a phase III clinical trial comparing OFS+ET to ACT+OFS+ET. Methods: We hypothesize that addition of ACT to OFS+ET is superior to OFS+ET in improving invasive breast cancer-free survival (IBCFS) among premenopausal pts with early-stage HR+/HER2– tumors, and a 21-gene RS between 16-25 (for pN0 pts) and 0-25 (for pN1 pts). Secondary objectives include invasive disease-free survival, overall survival, distant recurrence-free interval, breast cancer-free interval, and health-related quality of life (HRQOL). Pts must be node-neg with RS 16-20 (plus high clinical risk), RS 21-25, or have 1-3 positive nodes with RS ≤25. Stratification is by nodal status/RS status (pN0 RS 16-25; pN1 RS 0-15; pN1 RS 16-25), intent to receive CDK4/6 inhibitor (yes; no), and age (18-39; ≥40). Pts are randomized after surgery to either OFS+ET or ACT+OFS+ET. ET is an aromatase inhibitor (AI) per physician discretion; or tamoxifen if AI is not tolerated or if OFS is incomplete. Radiotherapy will be administered per protocol guidelines. An HRQOL sub-study will assess severe menopausal symptoms (measured by FACT ESS-19) and pain severity (PROMIS) between arms. Blood and tumor specimens will be collected for future research. We anticipate accrual of 3,960 pts in 7 yrs, 7 mos. Per NSABP B-28/RxPONDER data, 5-yr IBCFS of pN1 pts on the ACT+OFS+ET arm is estimated at 92.3%. Per TAILORx data, 5-yr IBCFS of pN0 pts on the ACT arm is ~95%. Assuming 56% of pts to be pN0 and 44% pN1, and a 0.5% annual loss-to-follow-up rate, the definitive analyses to detect a hazard ratio: 0.75 with ACT+OFS+ET v OFS+ET, with 1-sided α of 0.025 and 80% power, will require 380 IBCFS events, expected to occur ~11 yrs after study initiation. Accrual is 496/3,960 (from 8/2023 to 1/2026). NCT #: NCT05879926. Clinical trial information: NCT05879926 .

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