Breast cancer patients experience treatment-related pain from surgery, radiation, chemotherapy, and long-term hormonal treatment, which can lead to poorer outcomes. Patient and family caregivers’ psychosocial distress exacerbates patient pain interference, but this has not been directly examined among breast cancer patients in dyadic models longitudinally. Guided by a biopsychosocial framework, the Biobehavioral Family Model, we explore how multiple reports of patient pain interference across the first year of treatment are linked to patient (N = 55) and caregiver (N = 55) pre-treatment psychosocial distress (e.g., depression, anxiety, marital satisfaction, family relationship quality). Specifically, we find that breast cancer patients’ pain interference increases and then decreases over the first year of treatment. Additionally, caregivers’ pre-treatment anxiety was associated with increased patient pain interference over time (B =.19, SE =.07, p =.008), while patients’ pre-treatment psychosocial distress was not associated with a change in their pain interference. Yet, looking at clinically specific times during the first year of treatment, we find that caregiver-reported higher marital satisfaction is associated with lower patient-reported pain interference later in treatment (6-months: B = -.58, SE =.24, p =.017; 12-months: B = -.82, SE =.23, p <.001). We conclude that, per the Biobehavioral Family Model, pre-treatment patient and caregiver psychosocial distress is linked to patient pain interference during the first year of breast cancer treatment. Thus, caregivers' psychosocial distress (i.e., anxiety and marital satisfaction) may be a particularly important target in future dyadic behavioral intervention strategies to reduce breast cancer patient pain. PERSPECTIVE: This article presents the link between breast cancer patients and family caregiver pre-treatment psychosocial distress (anxiety, depression, marital satisfaction, and family quality) on patient pain interference during one year of breast cancer treatment. Findings suggest that caregiver anxiety and marital satisfaction may be important targets for future dyadic behavioral pain interventions.Copyright © 2024. Published by Elsevier Inc.