Abstract Background: While survival for patients with early breast cancer (eBC) has greatly improved with earlier detection and modern treatments, the risk of recurrence and long-term/late treatment-related adverse events (AEs) remain concerns for many patients. Contemporary real-world data are needed to understand current diagnostic pathways, treatment patterns and toxicities, quality of life, and patient experience to better characterize eBC care and knowledge gaps and establish important hypotheses to test in prospective trials, with the ultimate goal to improve both treatment and outcomes for patients with eBC. Study design: PicnicHealth and AstraZeneca are collaborating to build a real-world observational eBC cohort composed of de-identified medical records data supplemented with patient-reported outcomes (PROs), including patient-reported social determinants of health (SDoH). Patients recruited from multiple channels, such as digital marketing and community partnerships, will consent to participate and sign HIPAA authorization for PicnicHealth to collect their medical records from all providers and sites of care in the United States. All available retrospective medical records in any format will be retrieved, and records will continue to be collected for patients prospectively following enrollment. Disease-specific information will be abstracted using PicnicHealth’s human-in-the-loop machine learning abstraction platform. Patients will have access to their records in the form of a searchable and shareable digital timeline. Additional data, including but not limited to symptoms, quality of life and treatment experience will be collected through surveys. The first patient was enrolled in May 2023. Patients will be followed for ≥8 years or until withdrawal or death, whichever occurs first. Eligibility criteria: Patients with stage I-III breast cancer diagnosed ≤3 years before enrollment, who onboard to the PicnicHealth platform, consent to participate, sign HIPAA authorization for medical record collection, and provide ≥1 provider/care site for record retrieval will be included in the cohort. Specific aims: The cohort aims to generate contemporary real-world data relevant to understanding demographic and clinical characteristics, SDoH, diagnostic/testing pathways, treatment patterns, and clinical outcomes, including AEs and AE management. Specifically, demographic and SDoH differences in management, outcomes, and the patient experience during and following eBC diagnosis and treatment will be evaluated. The cohort design and the data collected will evolve as the eBC landscape evolves to continuously address new research questions around diagnosis, management, outcomes, and patient experience. Statistical methods: The demographics, SDoH, clinical characteristics, treatments, healthcare resource utilization, eBC outcomes, such as recurrence and progression, and patient experience will be summarized for the cohort overall and by pre-determined subgroups using descriptive statistics. Additional analyses include, but are not limited to, evaluating the impact of key exposures, such as SDoH, on treatment and diagnostic pathways, treatment compliance, clinical outcomes, and PROs. All analyses will be prespecified in study-specific statistical analysis plans. Present accrual and target accrual: At least 3,000 patients will be enrolled in the PicnicHealth eBC Cohort. As of July 2023, 843 patients have onboarded to the PicnicHealth platform and will be screened for eligibility into the eBC registry cohort. Contact information for people with a specific interest in the study: For additional information, please contact breastcancer@picnichealth.com. Citation Format: Haley Friedler, Meghan Tierney, Melinda Baker, Gillian Hanson, Josefa Briceno, Karen Smith, Michele Baber, Kara Glover, Xiaoqing Xu, Kellie Ryan, Zulikhat Segunmaru, Clara Lam, Maryam Lustberg, N. Lynn Henry, Rachel Greenup, Marianna Chavez, Joseph Unger, Alice Ho, Deborah Collyar. EVOLVE: An Ambispective, Patient-Centered, Real-World Early-Stage Breast Cancer Study in the United States [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 PO5-19-04.