Abstract Background/Purpose: Language concordance is critical for effective communication between patient and provider. Compared to the percentage of primary Spanish speakers in California, there is a lack of Spanish-speaking providers in healthcare, especially in oncology. In-house hospital interpreters help overcome basic language barriers; however, even with the adoption of these services, there remain gaps in comprehension. Such gaps in communication can compromise the informed decision-making process, necessitating novel approaches to multilingual health communication. This study aimed to (a) explore language barriers Hispanic/Latino patients and their caregivers face when navigating rectal cancer care services and (b) propose a culturally-tailored solution that could address these barriers. Methods/Study Population: We designed a community-based participatory study using qualitative methods. Specifically, we formed a Community Advisory Board and partnered with local promotoras – health navigators with strong ties to the Hispanic/Latino community. Together, we developed a semi-structured interview guide to shape our conversations with individuals residing in the Bay Area or the San Joaquin Valley who identify as Hispanic/Latino, and who reported having either a past or current rectal cancer diagnosis. We also invited their caregiver(s) to attend the interview. Interviews lasted 45-60 minutes in English or Spanish. Over a 6-month period, twenty interviews were conducted with patients alone (n= 14), a caregiver alone (n=2), and patient-caregiver pairs (n=4). Data analysis utilized grounded theory and reflexive thematic analysis to identify core themes. Results: Themes that arose include (1) ineffective and non-satisfactory communication through electronic interpreter services, (2) bilingual caregiver burden in reinforcing interpreter translations due to dialect differences, (3) patients not actively seeking out translation services for concern of causing inconvenience to the healthcare team, (4) patients’ preferred language not accurately captured in the electronic medical record. Conclusion: Interpreter services have helped bridge the language gap in healthcare, but inevitable gaps remain as language involves more than just the spoken word; it includes the culturally influenced non-verbal cues and the management of emotional responses to the information provided, components of communication which interpreters may miss. A solution to address the cultural complexities of language among this population in this setting, could be the adoption of promotoras; these health navigators share multiple aspects of their cultural identities with the patient population, making them uniquely positioned to bridge the gap between the medical system and the Hispanic/Latino community. Citation Format: Eleanor Brown, Julian P Howland, Min Y. Kim, Lucas K. Carpenter, Patricia Castañeda, Maria Gonzalez, Miriam T. Hernandez, Zaria N. Cosby, Kristen M. Davis-Lopez, Ysabel Duron, Gladys M. Rodriguez, Sandra S. Zaky, Arden M. Morris, Aaron J. Dawes. La lengua materna: Understanding language challenges experienced by Latino patients and caregivers in rectal cancer care [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr B077.