235P Advancing treatment choices: CDK4/6 inhibitor switching in HR+/HER2- metastatic breast cancer

CDK4/6 inhibitors (CDK4/6i) use has revolutionized the treatment of hormone receptor-positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer. The choice of a specific CDK4/6i may be influenced by adverse events (AEs). Recently, the Italian Medicines Agency (AIFA) approved the possibility of switching between CDK4/6i for unacceptable toxicity. With the support of the Italian Association of Medical Oncology (AIOM), we conducted a survey among 92 oncologists to assess the impact of AIFA's approval on patient management. The survey addressed treatment discontinuation for toxicity, exploring oncologists' experiences and future perspectives on CDK4/6i switch. The survey showed that 48% of participants were not surprised regarding AIFA's decision, with 76% of respondents believing that this opportunity would significantly influence their treatment choices, enhancing AEs management for patients. Yet, 49% of respondents emphasized the need for more real world evidence on the safety and efficacy of CDK4/6i switch. 96% of respondents reported discontinuation rates between 0%-25% of patients, with constipation and hematological toxicity being the most frequent reasons for treatment discontinuation. The oncologists prescribing CDK4/6i switch reported that most of these patients were in first-line treatment (85%) and the most common switch to the second CDK4/6i that was most frequently initiated was palbociclib (69%), then abemaciclib (17%) and ribociclib (14%). Among those who started the second CDK4/6i at full dosage, 66% of patients did not require a dose reduction. Our survey highlights the importance of allowing CDK4/6i switching, thus likely prompting oncologists to adapt their treatment choices, leading to better management of AEs for improving patients' outcome.