12049 Background: Prior studies suggest that social support plays a role in disease understanding of older patients with advanced cancer. In this study, we examined the association of quantity and quality of social support with belief in curability among older patients with advanced incurable cancer. Methods: We performed a secondary analysis of a cluster-randomized geriatric assessment trial (URCC 13070: PI Mohile) that recruited older adults (≥70) with advanced incurable cancer and caregivers. At enrollment, patients completed the Older Americans Resources and Services (OARS) Medical Social Support form to measure both quantity (number of close friends and relatives) and quality of social support. Quality of social support was measured using twelve questions, each ranged from 1 (none of the time) to 5 (all of the time). Higher cumulative scores indicated greater quality of support. For beliefs in curability, patients were asked, “What do you believe are the chances that your cancer will go away and never come back with treatment?” Responses were 0%, <50%, 50/50, >50%, and 100%. Ordinal logistic regression was used to investigate the association of social support with beliefs in curability, adjusting for adjusting for age, gender, education, race, number of Geriatric Assessment (GA) impairments, cancer type, and locality (rural versus urban). Results: We included 347 patients; mean age was 76.4 years, 91% were white, 52% were male, 46% had household income <$50,000, and 55% had high school degree or higher. For every unit increase in OARS Medical Social Support score, the odds of believing in curability decreases by 36.4% [Adjusted Odds Ratio (AOR) 0.733, 95% Confidence Interval (CI): (0.555, 0.969)], after controlling for covariates. Quantity of social support was not associated with belief in curability [AOR 1.033 95% CI: (0.921, 1.156)]. Conclusions: Our study revealed that older patients with advanced cancer who felt more supported by their social network were more likely to report that their cancer was not curable. Interventions that improve quality of social support may also affect disease understanding. Funding: Patient-Centered Outcomes Research Institute (PCORI) 4634 and NIH K24 AG056589 to SGM, NCI UG1CA189961, T32CA102618, NCI K99CA237744 to Loh.