TPS1132 Background: Current evidence from both randomized trials and real-world evidence studies suggests that older patients with advanced hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer derive clinical benefit from the addition of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors to endocrine therapy. However, a higher risk for adverse events due to CDK4/6 inhibitors among older patients is evident, leading to a trend of initiating CDK4/6 inhibitors at a lower dose in clinical practice, though without evidence. The aim of the present randomized trial is to investigate whether lower initial dose of CDK4/6 inhibitors combined with endocrine therapy is comparable to full dose in older patients with advanced HR+/HER2-breast cancer that are assessed as vulnerable/frail based on comprehensive geriatric assessment (CGA). Methods: We designed a multi-national, open-label, pragmatic randomized controlled trial with non-inferiority approach. Patients ≥70 years old with advanced HR+/HER2- breast cancer with no curative intention, no prior treatment in an advanced setting, and suitable to receive a combination of CDK4/6 inhibitors plus endocrine therapy according to treating physician, are eligible for study inclusion. After informed consent, included patients fill out a self-administered CGA tool and categorized accordingly to fit, vulnerable, or frail, depending on the number of impaired CGA domains. Fit patients receive full dose of CDK4/6 inhibitors and endocrine therapy whereas vulnerable/frail patients are randomized to either -1 level lower CDK4/6 inhibitor dose or full dose and endocrine therapy. The randomization is stratified by type of CDK 4/6 inhibitor, type of endocrine therapy, and level of vulnerability. The treating physician decides on the choice of CDK4/6 inhibitor (abemaciclib, ribociclib, palbociclib) and endocrine therapy (aromatase inhibitors, fulvestrant). The primary endpoint is time to treatment failure whereas secondary endpoints include overall treatment utility, progression-free survival, overall survival, time to chemotherapy initiation, toxicity, quality-of-life, time to quality-of-life deterioration and cost-effectiveness. The evaluation of disease progression, toxicity assessment, and the follow-up strategy resembles clinical practice to enhance the pragmatic design approach of IMPORTANT trial. The trial also enables a hybrid decentralized approach where the initial patient visit is in-person whereas the visits for efficacy and toxicity evaluation can be performed digitally according to local practices. In total, 495 patients are planned to be included to allow 346 vulnerable/frail patients to be randomized. Enrollment: The trial is open for recruitment since February 2024 with a recruitment period of 30 months. Clinical trial information: NCT06044623 .
