Background: Older patients with advanced cancer often have comorbidities that increase the risk of toxicity from neoplastic therapy but are not always considered in treatment planning. We assessed the utility of a geriatric assessment (GA) intervention to increase the number and quality of discussions about comorbidities among oncologists, older patients, and caregivers. Methods: This multi-site trial enrolled patients who were ≥70 years, had advanced solid tumors or lymphoma, had ≥1 GA impairment, and who were considering or receiving cancer treatment. All patients received the GA and completed an Older Americans Resources and Services Comorbidity survey, which evaluated 15 conditions and interference with activities (clinical impairment = ≥3 comorbidities or ≥1 highly interfering). Oncology practices were randomized to intervention (GA with a summary with management recommendations provided to oncologists) or usual care (GA only). The clinic visit after GA was audio-recorded, transcribed, and coded for GA topics including comorbidity. Generalized linear mixed models adjusting for site (random effect) were used to assess the effect of the intervention. Results: Patients (n=527 evaluable, 76.6±5.2 years, 49% female) and oncologists (n=131, 63 in intervention) were enrolled from 31 sites. In total, 94.5% of patients had ≥1 comorbidity with an average of 3.2±1.9; 64% were clinically impaired by comorbidity (p=0.76 between arms). The intervention arm had twice the number of conversations about comorbidities (1.02 vs. 0.52 conversations per patient, difference 0.50, 95% CI 0.18-0.81, p=0.004) and conversations were more likely to be initiated by the oncologist (p<0.001, Table). Moreover, among patients who had conversations about comorbidities, more patients in the intervention arm had discussions specifically addressing comorbidities (e.g., cancer treatment modification, communication with the primary care physician; 24.3% vs. 7.5%, p=0.003). Conclusions: Providing oncologists with a GA summary and recommendations encouraged them to engage in more discussions about their patients’ comorbidities with the goal of addressing interactions between comorbidities, cancer, and its treatments. Funds: PCORI CD4634, NCI UG1CA189961 Clinical trial information: NCT02107443.