Drug-drug interactions (DDIs) in elderly patients with metastatic renal cell carcinoma (mRCC) treated with cabozantinib within the multicenter prospective trial ZEBRA/MeetURO 9.

648 Background: The oral tyrosine kinase inhibitor Cabozantinib (CABO) is frequently used to treat patients with metastatic RCC. Polypharmacy is common in elderly pts, thus several drug-drug interactions (DDIs) with cabozantinib may ensue. Methods: ZEBRA /MEET-URO 9 was a prospective, real world trial enrolling pts ≥ 70 years with mRRC treated with CABO at 13 Italian Oncology Centers. All concomitants drugs administered to pts were collected and categorized according to active principles and indication. DDIs were identified through a dedicated software (Lexicomp), scientific databases (Sider4.1) and published articles. Results: we enrolled 104 pts, median age 75.8 years (range 70.2-87.4 yrs). Overall, 91.4% of the cohort was treated at a reduced dose either upfront or due to side effects. Pts took a median of 6 concomitant drugs (IQR: 4-9), for a total of 131 active principles. Software analysis identified 4 DDIs (warfarin, apixaban, diltiazem and furosemide); whereas scientific reports allowed us to identify 15 additional DDIs involving metoprolol, nebivolol, olmesartan, amiloride, simvastatin, rosuvastatin, polyenoic omega-3 fatty acids, loperamide, metoclopramide, metformin, dutasteride, dexamethasone, prednisone, cetirizine and doxazosin. Seventy pts with potential DDIs experienced a trend for higher rate of grade 3-4 adverse events compared to other pts, although difference was not statistically significant (48.7% v 23.5 %, p=0.485). The table summarizes the main DDIs and suggestions to avoid or mitigate their effects Conclusions: the risk of DDIs was not negligible in our cohort of elderly mRCC pts treated with CABO, although the frequent dose reductions of CABO probably confounded their impact on toxicities. Unremitting attention to concomitant medications in the elderly is thus warranted. [Table: see text]