Wolmark, N.

Abstract PURPOSE: CDK4/6 inhibitors (CDK4/6i), used in combination with endocrine therapy (ET), are standard of care for advanced and higher risk early stage hormone receptor-positive (HR+), HER2 negative (HER2-) breast cancer. PALLAS investigated the addition of 2 years (y) of palbociclib to adjuvant ET (ET/P) compared to ET alone in patients (pts) with stage II-III HR+/HER2- breast cancer. We now present overall survival (OS) with 7-y outcomes and impact of post-recurrence therapy. PATIENTS AND METHODS: This global phase III trial randomized pts to ET for at least 5 y with or without 2 y of P. Primary endpoint was iDFS; distant recurrence-free survival (DRFS) and OS were preplanned endpoints. Kaplan Meier estimates and hazard ratios (HR) from Cox and Fine & Gray models were performed. Post-recurrence OS was analyzed as time from first distant recurrence (DR) until death. The post-recurrence OS model adjusted for both clin/path factors (including DR-free y, DR site) and time-dependent post-DR therapy (chemo, CDK4/6i). Results: 5,796 pts enrolled at 406 centers in 21 countries worldwide over 3 y. In the intent-to-treat (ITT) population, with a median follow-up of 82.7 months (mo), 7-y outcomes for iDFS, DRFS and OS are shown in the table. DR occurred in 781 pts (377 ET/P, 404 ET alone) with balanced pt/disease characteristics between arms. ET/P had more visceral (46% vs. 36%) and fewer non-visceral (61% vs. 68%) DR compared to ET alone (p=0.03). Unadjusted post-recurrence OS was significantly worse for ET/P vs. ET (median 22.6 vs. 27.9 mo, HR 1.21 (95% CI 1.01-1.46, p=0.04). However, receipt of any post-recurrence CDK4/6i was significantly higher on ET vs. ET/P arms (41% vs. 66%) and time to post-progression CDK4/6i initiation was significantly shorter for those in the ET vs. ET/P arms (HR 0.50, 95% CI 0.41-0.61, p<0.001) adjusting for region, bone/visceral DR type, DR-free time and age. Conversely, time to post-progression chemotherapy initiation was significantly longer for ET alone vs. ET/P arms (HR 1.31, 95% CI 1.07-1.61, p=0.01). However, after adjustment for clinical factors and post-DR treatment, the OS difference was no longer seen (HR 1.05, 95% CI 0.85-1.28, p=0.65). 3-mo landmark analysis showed similar effect on OS after adjusting for CDK4/6i initiation within 3 mo from DR (unadjusted HR 1.24, p=0.03 vs. adjusted HR 1.15, p=0.22). CONCLUSION: The PALLAS trial revealed significant differences in treatment post-DR that impact OS. Reduced/delayed use of metastatic CDK4/6i after adjuvant P was associated with significantly poorer OS, suggesting that patients who relapse after adjuvant CDK4/6i may still benefit from metastatic CDK4/6i. This has implications for optimal treatment in those who relapse after adjuvant CDK4/6i and warrants further study to determine if this is therapy-specific or an overarching biological effect. SUPPORT: AFT, ABCSG, NRG, PrECOG; Pfizer Citation Format: A. DeMichele, A. Dueck, M. Gnant, D. Hlauschek, M. Martin, A. Wolff, G. Rubovsky, F. Henao, O. Hahn, A. Chan, A. Brusky, P. Morris, H. Burstein, G. Huber, D. Anderson, L. Garcia-Estevez, G. Pfeiler, H. Rugo, N. Zdenkowski, S. Gampenrieder, N. Wolmark, D. Sabanathan, K. Miller, D. Cameron, E. Winer, C. Brunner, E. Gauthier, P. O’Brien, C. Fesl, E. Mayer. Adjuvant Palbociclib for ER+ Breast Cancer in the PALLAS Trial (ABCSG-42/AFT-05/PrE0109/BIG-14-13): Post-Recurrence Treatment and Overall Survival [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr RF7-07.

Abstract As shown by the TAILORx and RxPONDER trials, recurrence score (RS) identifies many postmenopausal pts who do not benefit from addition of ACT to endocrine therapy (ET); however, it also identifies certain subsets of premenopausal pts 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 the SOFT/TEXT trials, we question whether the noted ACT benefit in TAILORx/RxPONDER may have been the result of chemotherapy-induced OFS. To address this, we developed OFSET, a phase III clinical trial comparing OFS+ET v ACT+OFS+ET. We hypothesize that addition of ACT to OFS+ET is superior to OFS+ET in improving invasive breast cancer-free survival (IBCFS) among premenopausal, early-stage BC pts with 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), or RS 21-25, or have 1-3 positive nodes with RS ≤25. Stratification is by nodal status/RS status (pN0 RS 16-25 v pN1 RS 0-15 and pN1 RS 16-25), intent to receive CDK4/6 inhibitor (yes; no), and age (18-39 v ≥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. The HRQOL substudy will assess differences between arms in severe menopausal symptoms (measured by FACT ESS-19) and pain severity (PROMIS). 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%. Based on 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 292/3,960 (from 8/2023 to 5/2025). Among 148 pts with OFS data available, 79 (53.4%) were prescribed goserelin and 69 (46.6%) leuprolide. A monthly dosing schedule was prescribed for 86.1% of pts receiving goserelin and 73.5% of those receiving leuprolide; the remaining received a 3-monthly schedule. NCT05879926 Support: U10 CA180868, -80822, UG1 CA189867, U24 CA196067 Citation Format: S. Swain, G. Tang, S. L. Puhalla, P. A. Ganz, N. L. Henry, R. S. Cecchini, S. A. Reid, P. Rastogi, C. E. Geyer, Jr., J. R. White, A. S. Clark, T. C. Haddad, G. A. Vidal, N. Wolmark, E. P. Mamounas. NRG-BR009: 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 recurrence score ≤25 (OFSET) [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-07-04.

Abstract Background: Approximately 50% of newly diagnosed invasive breast cancers are stage 1, with the majority being ER/PR-positive, HER2-negative. Genomic assays such as the Oncotype DX® have identified patients (pts) with reduced risk of distant metastasis and without benefit from chemotherapy added to endocrine therapy (ET), freeing them from excess toxicity. Genomic assays are also recognized as prognostic for in-breast recurrence (IBR) after breast-conserving surgery (BCS) and could similarly allow de-escalation of adjuvant radiotherapy (RT). Reducing overtreatment is of interest to pts, providers, and payers. Methods: We hypothesize that BCS alone is non-inferior to BCS plus RT for IBR and breast preservation in women intending ET for stage 1 invasive breast cancer (ER and/or PR-positive, HER2-negative with an Oncotype DX Recurrence Score [RS] of ≤18). Stratification is by age (<60; ≥60), tumor size (≤1 cm; >1-2cm), and RS (≤11, >11-18/MammaPrint Low). Pts are randomized post-BCS to Arm 1 with breast RT using standard methods (moderate or ultra hypo- or conventional-fractionated whole breast RT with/without boost, or APBI) with ≥5 yrs of ET (tamoxifen or AI) or Arm 2 with ≥5 yrs of ET (tamoxifen or AI) alone. The specific regimen of ET in both arms is at the treating physician’s discretion. Eligible pts are stage 1: pT1 (≤2 cm), pN0, age ≥50 to <70 yrs, s/p BCS with negative margins (no ink on tumor), s/p axillary nodal staging (SNB or ALND), ER and/or PR-positive (ASCO/CAP), HER2-negative (ASCO/CAP), and Oncotype DX RS ≤18 (diagnostic core biopsy or resected specimen). A “low risk” MammaPrint is permissible if completed as part of usual care prior to screening. Primary endpoint is IBR (invasive breast cancer or DCIS). Secondary endpoints are breast conservation rate, invasive in-breast recurrence, relapse-free interval, distant disease-free survival, overall survival, patient-reported breast pain, patient-reported worry about recurrence, and adherence to ET. We assume a clinically acceptable difference in IBR of 4% at 10 yrs to judge omission of RT as non-inferior (10-yr event-free survival for RT group is 95.6% v 91.6% for the omission-of-RT group). BR007 is powered to detect non-inferiority with 80% power and a one-sided α=0.025, assuming that there would be a ramp-up in accrual in the first two years (leveling off in Yrs 3-5); 1,670 pts (835 per arm) are required for randomization. Conservative loss to follow-up is 1%/yr. Some T1a pts screened may have Oncotype DX scores >18, making them ineligible for the study. In the accrual process, 1,714 pts will be required to register to ensure that our final randomized cohort is 1,670 pts. As of July 9, 2025, 1,490 pts have been screened and 1,349 randomly assigned. NCT #: NCT04852887 Support: U10 CA180868, -180822, U24 CA196067, UG1 CA189867 Citation Format: J. R. White, R. S. Cecchini, E. E. Harris, E. P. Mamounas, J. G. Bazan, D. G. Stover, P. A. Ganz, R. Jagsi, S. J. Anderson, C. Bergom, V. Théberge, M. B. El-Tamer, R. C. Zellars, D. A. Shumway, G. Chen, T. B. Julian, N. Wolmark. A phase III trial evaluating De-escalation of Breast Radiation (DEBRA) following breast-conserving surgery of stage 1, HR+, HER2-, RS ≤18 breast cancer: NRG-BR007 [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-08-20.