2145P Thromboembolic disease associated with cyclin-dependent kinase inhibitors in patients with breast cancer

The risk of venous and arterial thromboembolic events (VTE/AT) secondary to cyclin-dependent kinase inhibitors (CDKI) is not clearly defined. The objective is to characterize VTE/AT in patients with breast cancer (BC) treated with CDKI. Retrospective, multicenter study promoted by the Thrombosis and Cancer Section of the Spanish Society of Medical Oncology (SEOM). Individuals with BC who initiated CDKI between 2015 and 2021 were recruited. We performed a descriptive analysis, analyzed the impact of VTE/AT on survival using Kaplan-Meier models and determined predictor variables using multivariate logistic regression. 849 patients were enrolled, with a median follow-up of 24 months. The incidence of VTE/AT during follow-up was 5.5% (n=47), with 34% pulmonary embolism (PE), 27.7% deep vein thrombosis (DVT), 14.9% simultaneous PE and DVT, 12.8% other forms of venous thrombosis, 8.5% arterial thrombosis and 2.1% mixed event (venous and arterial). Median time to VTE/AT was 6.9 months (interquartile range: 2.7-15.8). 31.9% of the events were diagnosed incidentally and 85.1% in an outpatient setting. One patient (2.1%) had recurrence and two (4.7%) had major bleeding. A higher proportion of thrombotic events was observed with abemaciclib (9%) compared to palbociclib (4.6%) and ribociclib (5.4%), but the differences were not significant (p=0.119). We found an association (p=0,036) between the type of CDKI and the form of VTE/AT: the most frequent with palbociclib was DVT (40.9%), with ribociclib arterial thrombosis (33.3%) and with abemaciclib PE (46.2%). Median overall survival was 49 months (95% CI 43-55.5) in the subgroup without VTE/AT, while in patients with VTE/AT it was not possible to calculate due to the low number of events. There were no significant differences (log-rank test = 0.427). Multivariate analysis revealed that the presence of metastases in the central nervous system (CNS) was associated with an increased risk of VTE/AT (OR 3.289, 95% CI 1.06-10.2). CDKI-associated VTE/AT in patients with BC does not impact on survival. The type of CDKI is related to the form of presentation of VTE/AT. The presence of CNS metastases may predict these events.