243P Concomitant administration of palbociclib and proton pump inhibitors affects clinical outcomes in metastatic breast cancer patients

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are usually combined with fulvestrant or aromatase for the treatment of patients metastatic breast cancer (mBC). Drug-drug interactions may affect absorption by different mechanims, instance, modification digestive pH. Proton pump (PPIs) known to reduce oral bioavailability some anticancer drugs. Palbociclib is a weak base pH-dependent solubility, therefore variations in gastric pH could its absorption. The objective this study was evaluate interaction between PPIs palbociclib analizing progression-free survival (PFS) mBC. This retrospective approved local Ethics Committee. Patients had received January 2016 December 2021. following variables were collected: age, menopausal status, performance hormonal (fulvestrant inhibitors), visceral non-visceral disease, first-line vs second-line treatment, ki67, concomitant use PPIs. PFS defined as time from starting progression disease. Survival estimated Kaplan-Meier method, whereas Cox Regression models used estimate hazard ratios chi-square test categorical variables. A total 169 enrolled study: 80 PPI 86 did not, without significant differences clinical characteristics both groups. median 17.3 months (95% CI: 13.83-20.76), 36 13 second subsequent lines. taking shorter (14.30 versus 42.6 months, p<0.001; HR 4.18: 95% CI 2.57-6.80; p<0.0001). Median 44 vs. 14 ans 17 9 line (first beyond) ki67 influence on DFS, remaining not. mBC treated therapy plus poor when receving PPI. Although further studies needed field, caution recommended long-term population.