Abstract Breast cancer is the leading cause of cancer-related mortality for Latinx women in the US. Compounding this challenge is low representation of Latinx patients (pts) in cancer research studies. Neglecting Latinx participation limits scientific understanding and the development of effective therapies for all pts. To address this disparity and increase research accessibility, we collaborated with Latinx community (comm) members and translated all aspects of an existing patient-partnered research project, The Metastatic Breast Cancer Project (MBCproject), into Spanish. The MBCproject (MBCproject.org) is a research study that directly engages pts through social media and advocacy groups, empowering pts to share their samples, clinical information, and experiences. Despite having 3,300 consented participants, only 3.7% (123) identify as Hispanic, Latinx, or Spanish. With the Latinx population increasing in the US and cancer’s impact on the comm, it is imperative that Latinx individuals participate in cancer research. Native Spanish speaking members on the MBCproject team leveraged the existing MBCproject model of direct collaboration with pt communities to translate pt-facing materials. Pts and pt advocates provided feedback on site content, project name, surveys, and biospecimen kit instructions through video calls with team staff. Over 17 months, 6 focus groups were held with 9 members of the comm, assessing 6 different material items. Iterations of the materials discussed were shared via email to complete the process. Proposed Spanish language dialect, pronoun formality, and transparency in project content were also reviewed to ensure messaging resonated with the broader Latinx comm. Following comm review, modifications were integrated into materials. A Mexican- Spanish dialect and formal pronouns were chosen to be used across all materials. The project name remained to maintain continuity across languages. Distinct feedback included simplified terminology and materials that could be shared with their health care provider. Clarity in tissue acquisition, privacy of data collected, and participation requirements was also requested. Attendance of study staff at Latinx cancer disparities research conferences revealed interest amongst investigators for more comprehensive demographic data collection of Latinx pts in studies, leading to the development of more detailed race and ethnicity questions in our intake survey. Finalized project materials have been submitted for IRB approval and expected to be launched at mbcprojectenespanol.org in Fall 2020. This partnered approach has led to an inclusive set of materials embraced by the Latinx pts and pt advocates who have helped us develop the MBCproject in Spanish. This is a foundational pilot that will allow Spanish speaking participants to engage in cancer research without a language barrier and contribute to the acceleration of scientific discoveries that impacts their community. Citation Format: Tania G. Hernandez, Sara Balch, Jorge Buendia- Buendia, Jorge Gomez Tejeda Zanudo, Mary McGillicuddy, Colleen M. Nguyen, Foxy Robinson, Corrie Painter, Elana Anastasio, Michael Dunphy, Nikhil Wagle. The Metastatic Breast Cancer Project in Spanish: Developing a Spanish language patient-partnered research project with the Latinx community through culturally appropriate materials [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-015.