PROJECT SUMMARY/ABSTRACT More than 80% of breast cancer survivors and nearly all family caregivers experience unmet supportive care needs during cancer treatment and throughout survivorship. These unmet supportive care needs are key factors that contribute to poor quality of life for cancer survivors and their caregivers. Emotional, informational, and relational needs are among the most reported unmet needs by cancer survivors and their caregivers, and result from gaps in cancer care services. Interventions to support the unmet needs of cancer survivors have provided no evidence of an underlying mechanism for reducing unmet needs for the survivors, and many caregiver interventions have yielded small effects. Given the known interdependence between cancer survivors and family caregivers’ well-being and the promising effects of mindful resilience-based interventions in other populations such as transplant patients, a systems-level resilience-based approach may be key in addressing these unmet needs. Family resilience, or the ability of family to rebound and grow from adversity, is associated with greater quality of life in cancer survivors and their caregivers. While the relationship between family resilience and unmet needs is unknown, there is evidence that more individual or intrapersonal resilience is associated with fewer unmet supportive care needs. Furthermore, as unmet needs change over the course of the illness trajectory and throughout survivorship, identifying a mechanism that adapts over time and leverages the strengths of the family to cope and manage needs is crucial. This observational cross- sectional study aims to determine the relationship between unmet supportive care needs, family resilience, and quality of life in breast cancer dyads (survivors and caregivers) during two phases of cancer care (active treatment and reentry phase). Using latent variable structural equation modeling, specifically the Actor-Partner Interdependence Model, we will exami