Background: Frailty is common in older adults undergoing major cancer surgery. Mounting evidence indicates multimodal interventions to optimize patient functional status by addressing vulnerabilities associated with frailty before surgery result in decreased complications and enhanced functional recovery. This study tested the effectiveness of OPTI-Surg, a surgical prehabilitation toolkit for improving surgical care and outcomes in older patients undergoing major cancer surgery. Here, we report results from the planned futility interim analysis (IA). Methods: Thoracic (T), gastrointestinal (GI), and urologic (GU) oncological surgery practices affiliated with NCI’s Community Oncology Research Program were randomized 1:1:1, stratified by practice type, to usual care (control), OPTI-Surg toolkit, or OPTI-Surg with an implementation coach. The toolkit was implemented at the practice level. It consisted of the 12-item Edmonton Frail Scale and guided recommendations for interventions directed at identified vulnerabilities. Eligible patients were adults ≥70 years old undergoing curative intent surgery for lung, gastrointestinal, or urologic cancers. Primary outcome was 8-week post-operative function (weekly caloric expenditure) derived from the validated Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire. A linear mixed model was used to compare usual care to the 2 OPTI-Surg arms combined, controlling for baseline function. Results: From July 2019 to October 2021, 225 patients, 50% of the total accrual goal, were enrolled from 29 practices, triggering the IA. Study was suspended to new patient accrual March to June 2020 due to the COVID-19 pandemic. There were no differences in demographics by arm (mean age 76.2 years; 46.4% women; 79.6% white; 20.4% lung resection, 69.8% major GI surgery, 9.8% total cystectomy). Of the 225 patients, 140 (47 Usual Care, 93 OPTI-Surg) were evaluable for the IA. There was no significant difference in post-operative function between OPTI-Surg and usual care (mean decrease of 0.59 kCal/week for OPTI-Surg patients and 0.19 kCal/week for usual care patients, p = 0.762, intraclass correlation = 0.033). Based on the futility analysis, the DSMB recommended closure of recruitment on September 16, 2022. Conclusions: Implementation of the OPTI-Surg toolkit did not significantly improve functional outcomes 8 weeks after surgery for patients aged 70 and older undergoing major cancer surgery compared to usual care. Future analysis of implementation and ethnographic data may identify reasons why significant differences between the intervention and usual care arms were not observed, potentially including disruptions due to the COVID-19 pandemic. Clinical trial information: NCT03857620.