IMPORTANCE: The functional status and physical performance of older adults with cancer are underassessed and undertreated despite the high prevalence of impaired functional status and physical performance in this population and their associations with chemotherapy-induced toxic effects and mortality. OBJECTIVE: To examine the association between providing oncologists with a geriatric assessment (GA) summary with recommendations and having oncologist-patient conversations about functional and physical performance. DESIGN, SETTING, AND PARTICIPANTS: Data for this secondary analysis were collected from October 29, 2014, to April 28, 2017, for a national cluster randomized clinical trial conducted by the University of Rochester Cancer Center National Cancer Institute Community Oncology Research Program evaluating the effect of a GA intervention on patient satisfaction with communication about aging-related concerns. There were 17 practice clusters in the intervention group and 14 in the usual care group. All 541 participants underwent a GA including standardized functional and physical performance measures and had 1 clinical encounter audio-recorded, transcribed, and blindly coded to categorize conversations by GA domain. Participants were aged 70 years or older, with a stage III or IV solid tumor or lymphoma with palliative treatment intent, and impairment in 1 or more GA domain. Statistical analysis was performed from August 18, 2020, to January 10, 2022. INTERVENTIONS: Oncologist practices randomized to the intervention received a GA summary and validated recommendations for each patient prior to the audio-recorded clinical encounter. MAIN OUTCOMES AND MEASURES: The primary analysis of this clinical trial assessed the effect of the intervention on patient satisfaction with oncologist communication about aging-related concerns. This secondary analysis assessed the post hoc hypothesis that the intervention would be associated with an increase in the proportion of patients having conversations with their oncologists and receiving oncologist recommendations specific to functional and physical performance concerns. RESULTS: A total of 541 patients (276 men [51%]; mean [SD] age, 77.5 [5.2] years [range, 70-96 years]) were analyzed at baseline. Excluding 13 patients without audio recordings, 86% of patients (95% CI, 78%-91%) in the intervention group vs 59% of patients (95% CI, 47%-69%; P < .001) receiving usual care had conversations about functional or physical performance. Conversations were more frequently initiated by oncologists in the intervention group (84%; 95% CI, 77%-90%) than oncologists in the usual care group (58%; 95% CI, 45%-70%; P < .001). Oncologists in the intervention group were more likely to address patients' concerns (43%; 95% CI, 33%-53%) than oncologists in the usual care group (17%; 95% CI, 10%-26%; P < .001). CONCLUSIONS AND RELEVANCE: In this secondary analysis of a cluster randomized clinical trial, providing oncologists with a GA summary was associated with an increase in the number of oncologist-patient conversations about functional and physical performance-related concerns with recommendations to address these concerns. These findings support the use of the GA summary and recommendations as important tools in caring for older adults with advanced cancer and functional or physical impairments. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02107443.