4CPS-032 Palbociclib and ribociclib: dose adjustment by toxicity and its impact in health outcomes

<h3>Background and Importance</h3> Most patients treated CDK4/6 inhibitors require dose adjustments due to toxicity. <h3>Aim and Objectives</h3> To analyse the toxicity associated with palbociclib and ribociclib leading to dose reduction and its weighting in health outcomes, measured in overall survival (OS). <h3>Material and Methods</h3> Descriptive, retrospective, single-centre study that included patients with hormone receptor-positive and HER2-negative advanced or metastatic luminal breast cancer treated with palbociclib or ribociclib between 1 January 2018, and 1 April 2022. Data analysis was completed on 31 January 2023. Demographic and clinical variables were obtained from the electronic medical record programme and treatment-related from the outpatient dispensing programme. Position measures (median and interquartile range) were used for quantitative variables and frequencies for qualitative, segmented by drug. Differences between drugs were assessed with statistical tests such as Kolmogorov-Smirnov, Shapiro-Wilk, Student’s t-test and Chi-squared. For OS, the Kaplan-Meier method and the Log-Rank test were applied, considering p values &lt;0.05 as significant (SPSSv28). <h3>Results</h3> Forty-five patients were included, all women. 51% were treated with palbociclib, the median age at treatment initiation was 61 years (IQR 51–67) for palbociclib and 53 years (IQR 46–62) for ribociclib. It was first-line treatment for 52% in palbociclib and 68% in ribociclib. 91% of the palbociclib group started full dose and 86% for ribociclib. 96% of the palbociclib group and 100% of the ribociclib group presented some toxicity, requiring dose adjustment in 43% and 50% of patients with palbociclib and ribociclib respectively. Among the toxicities that led to dose adjustment, neutropenia stands out (90% palbociclib and 55% ribociclib). Other toxicities that required adjustment for palbociclib group were asthenia and anaemia. And for ribociclib, dermal toxicity (27%), hypertransaminasemia and diarrhoea (9% in both). Without significant differences dose adjustment in both groups. The OS was 39.5 months (95% CI 31 to 48) for palbociclib and 29.1 months (95% CI 24 to 34) for ribociclib. No significant differences between both curves. p=0.47. <h3>Conclusion and Relevance</h3> Although no significant differences in toxicity management are observed between palbociclib and ribociclib in clinical practice, there are statistically proven differences in toxicities that motivate dose adjustment. The OS data obtained in both groups are comparable, which is expected since there are no differences in the management of dose adjustment. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest