Background: In research, how people act in close relationships is described as “attachment styles” which are composed of multiple attachment style dimensions (ASDs). Attachment avoidance is characterized by the need to isolate from the relationship (i.e. withdrawing and increased independence) while attachment anxiety is defined as needing reassurance and higher dependence. These two insecure ASDs are correlated with reduced quality of life for cancer patients (PT) and the family caregivers (CG). In ovarian cancer, PT and CG ASDs were correlated to dyadic coping, however 27% of PTs were disease-free. Attachment insecurity may be exacerbated by active treatment and uncertain prognosis. Therefore, we investigated the relationship between ASDs, and CG and PT reported dyadic coping and illness-specific communication. Methods: Metastatic sarcoma PTs and their CGs were recruited prospectively for a longitudinal, survey study investigating dyadic coping at Fred Hutchinson Cancer Center from Feb. 2022 – Dec. 2022. Participation rate for eligible PTs was 42% and 68% for CGs. Results are of participants who identified as intimate partners (individuals and dyads were allowed to participate). Attachment avoidance and attachment anxiety were measured via Relationship Structures Questionnaire. Dyadic coping and communication were measured via Dyadic Coping Inventory and Illness-Specific Relationship Talk (ISRT), respectively. Results: Sixty-nine participants enrolled: 43 PTs and 26 CGs (25 dyads). Participants were primarily non-Hispanic and white (91% PTs; 85% CG) with mean age 64 years (SD= 13.1; range = 26-89). 61% of PTs identified as men; 60% of CGs identified as women. CGs with attachment anxiety were more likely to report worse coping and less ISRT, while PTs with attachment anxiety were more likely to report only worse coping (See Table 1). However, PTs with attachment avoidance were more likely to report both worse coping and ISRT. Conclusions: Advance cancer PTs and their CGs with insecure ASDs report worse coping and communication. Screening for insecure ASDs may identify PTs and CGs who would benefit from supportive care, including psychotherapy. Future research should investigate this in a larger, more heterogenous population at earlier in the rare cancer trajectory and the effect of ASDs on PT, CG, and clinician communication.