Abstract PO1-01-01: ECOG-ACRIN EA1211: Interim FDG-PET/CT for predicting response of HER2-positive breast cancer to neoadjuvant therapy (DIRECT Trial)

Abstract Background: Strategies to optimize treatment decision-making in early stage HER2-positive breast cancer are a current priority for the oncology and patient advocacy community. Recent studies suggest that early metabolic changes on FDG-PET/CT (imaging biomarker) predict response to HER2-directed therapy. The TBCRC026 trial showed that participants not obtaining a 40% reduction in SULmax by cycle 1 day 15 (C1D15) following neoadjuvant trastuzumab/pertuzumab (HP) were unlikely to obtain pCR [negative predictive value (NPV) 91%]. The ECOG-ACRIN EA1211/DIRECT trial aims to validate FDG-PET/CT as a neoadjuvant interim (niFDG-PET/CT) imaging integral biomarker in patients treated with standard HER2-directed regimens (NCT05710328). Design: EA1211/DIRECT is a multicenter, single-arm, primary imaging phase 2 study enrolling patients with stage II/III HER2-positive breast cancer. Patients undergo standard skull base-thigh FDG-PET/CT at baseline and C1D15 and receive standard of care pertuzumab-based neoadjuvant therapy followed by surgery. Eligibility: Age ≥18 years, ECOG performance status 0-2, stage IIa-IIIc, untreated HER2-positive breast cancer with known hormone receptor status, suitable to undergo FDG-PET/CT imaging and neoadjuvant therapy. Methods: ΔSULmaxD15 will be computed as: (D15 SULmax – baseline SULmax)/baseline SULmax. The primary objective is to estimate the NPV of niFDG-PET/CT for pCR using ΔSULmaxD15 of the primary breast cancer at a threshold of 40%, in patients treated with neoadjuvant HER2-directed therapy. NPV is defined as the probability that pCR will not be achieved by participants with ΔSULmaxD15 < 40%. Secondary endpoints include evaluating the sensitivity, specificity, and positive predictive value of ΔSULmaxD15 of the primary breast cancer at a threshold of 40% and the ability of the niFDG-PET/CT biomarker to predict 3-year event free survival (EFS). Sample Size: We expect that 50% of patients will not reach the ΔSULmax threshold of 40% and a pCR rate of 40-60%. The proposed sample size is 210 participants, adjusted to 235 to account for missing data in 10% of cases. Computation of exact, two-sided 95% confidence intervals (CI) for NPV determined the lower limit of the CI is at least 80% when the true NPV is at least 88%. The lower limit is 84% when the true NPV has the value of 91%, which was estimated in the TBCRC026 study. Current Status: EA1211/DIRECT was activated in May 2023 across the NCI National Clinical Trials Network (NCTN), and accrual is anticipated to complete in March 2025. Those interested in the clinical trial can email ea1211team@ecog-acrin.org. Conclusion: The EA1211/DIRECT trial is the first step in implementing a Response-Guided Treatment Strategy by validating the ΔSULmax threshold of 40% as the optimum cut point across standard of care HER2-directed neoadjuvant regimens. If EA1211/DIRECT meets its objectives, the results will be used to design clinical utility studies, and thus hoping to change practice. Citation Format: Heather Jacene, Constantine Gatsonis, Roisin Connolly, Brian Burnette, Erica Stringer-Reasor, Maeve Hennessy, Justin Romanoff, Alexander Taurone, Ciara O'Sullivan, H. T. Carisa Le-Petross, Courtney Lawhn Heath, Vered Stearns, Amy Fowler, Shou-Ching Tang, Karla A Sepulveda, Angela DeMichele, David Mankoff, Antonio Wolff. ECOG-ACRIN EA1211: Interim FDG-PET/CT for predicting response of HER2-positive breast cancer to neoadjuvant therapy (DIRECT Trial) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-01.