Abstract GS2-07: Effect of Preoperative Breast MRI Staging on Local Regional Recurrence (LRR) in Early Stage Breast cancer: Alliance A011104/ACRIN 6694

Abstract Background: Despite its widespread adoption, there is a lack of data as to whether breast MRI for local staging and surgical planning of newly diagnosed breast cancer patients improves oncologic outcomes. The Alliance A011104 phase III trial was designed to test the hypothesis that MRI detection of mammographically occult disease helps to tailor surgical intervention thereby reducing local recurrence and improving local regional control. Here we report on the primary outcome of 5-year local regional recurrence. Methods: Patients with newly diagnosed clinical stage I-II, ER/PR- and HER2- negative (triple- negative) or ER/PR-negative and HER2-positive breast cancer, deemed eligible for breast- conserving surgery (BCS) based on clinical exam, mammography +/- ultrasound were randomized to undergo staging breast MRI or no further local staging. Patients with multifocal tumors that could be encompassed in a single operative resection were eligible. Patients who were carriers of gBRCA 1/2, or who had bilateral breast cancer, or a prior history of breast cancer were excluded. Initial eligibility was limited to patients not scheduled to receive neoadjuvant chemotherapy; however, a subsequent amendment allowed for enrollment after completion of neoadjuvant chemotherapy. Categorical variables were compared between arms with a chi-square or Fisher’s exact test. LRR, distant recurrence and overall survival (OS) were estimated with Kaplan-Meier point estimates and 95% confidence intervals (CIs). Hazard ratios (HRs) and 95% CIs were obtained from Cox proportional hazards models. Results: Of 319 patients enrolled from 2/2014-12/2019,161 were randomized to undergo breast MRI and 158 to no breast MRI evaluation. The mean age at enrollment was 58.9 years (range 29-85). Most patients (72.1%) had T1 tumors, 93.4% were cN0 and 19.7% were HER2 positive. Systemic chemotherapy was utilized in 85% with 17.6% receiving treatment neoadjuvantly; receipt of systemic therapy was unknown for 15 patients (4.7%). Two hundred and ninety-eight patients (93.4%) underwent surgical intervention; 91.9% underwent BCS as initial surgical procedure with no significant differences noted between groups (92.7% in the no MRI group and 91.9% in the MRI group p=0.62). Of patients who underwent breast surgery, 293 underwent axillary evaluation with the majority (270 patients, 92%) undergoing sentinel lymph node biopsy as the only axillary intervention. Among patients who received neoadjuvant chemotherapy, the overall pathologic complete response rate was 39.3%, 29.0%in the MRI arm vs. 52.0% no MRI arm (p=0.10). Receipt of adjuvant radiation was comparable between arms, 85.4% and 85.0% receiving radiation in the no MRI and MRI arms, respectively. Among 298 patients evaluable for the primary endpoint, with median follow-up of 61.1 months (0.2, 68.1), there were no differences in rates of LRR; 5-year local regional control was 93.2% (89.0-97.6%) in the MRI group and 95.7% (92.3-99.1%) in the no MRI group (HR: 1.1, 95% CI: 0.3, 3.9). For the entire cohort, 5-year distant recurrence-free rate and OS were 94.3% (91.7, 97.1) and 92.2% (89.1, 95.4), respectively, with no differences between groups. Conclusions: With multimodality therapy, rates of 5-year LRR in patients with early stage triple- negative and HER2-positive breast cancer are very low. Breast MRI for local staging and surgical planning in this setting does not result in improved local regional control. Support: U10CA180821, U10CA180882; UG1CA189823; U10CA180868 (NRG Oncology); ClinicalTrials.gov Identifier: NCT01805076; https://acknowledgments.alliancefound.org Citation Format: I. Bedrosian, K. Ballman, L. M. McCall, C. E. Comstock, G. W. Unzeitig, T. Yen, A. Weiss, B. G. Haffty, J. M. Bensenhaver, S. M. DeSnyder, J. J. Liu, A. H. Partridge, L. A. Carey, K. K. Hunt.Effect of Preoperative Breast MRI Staging on Local Regional Recurrence (LRR) in Early Stage Breast cancer: Alliance A011104/ACRIN 6694 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 GS2-07.