Background: The full dose of cabo is 60 mg, but some pts are treated with a reduced dose with the clinical anticipation of adverse events (AEs). We compared AEs and CO in mRCC pts treated with full versus reduced dose cabo. Methods: We performed a retrospective analysis of 65 mRCC pts treated with cabo at Winship Cancer Institute from 2016-2018. CO were measured by overall survival (OS), progression-free survival (PFS), and objective response (OR). OS and PFS were measured from first dose of cabo to date of death and clinical or radiographic progression, respectively. OR was defined as partial response (PR) or complete response (CR) per RECISTv1.1. AEs were collected from clinic notes. Univariate analysis (UVA) of association between AEs and CO was performed using logistic regression model. Results: Most pts were males (68%) and the median age was 63 years. Most (79%) had clear cell RCC (ccRCC) and the majority were IMDC intermediate (59%) or poor (39%) risk. Most pts (68%) received 60 mg and 48% of these pts underwent a dose reduction for AEs. Nearly all pts (95%) who started on a reduced dose experienced AEs, compared to 66% for pts treated with 60 mg. OR rate was similar for pts on 60 mg (18%) and pts on a reduced dose (19%). The median survival was comparable in pts treated with 60 mg and pts treated with a reduced dose (10.9 vs. 8.8 months, p=0.92 for OS and 5.6 vs. 5.1 months, p=0.23 for PFS) per Kaplan Meier estimation. AEs, particularly gastrointestinal (GI) AEs, were associated with significantly lower chance of OR (Table). Conclusions: CO may be comparable in mRCC pts treated with full versus reduced dose of cabo, but a reduced dose of cabo may not be associated with decreased AEs. GI side effects may be a poor prognostic factor in mRCC pts treated with cabo. Larger studies are warranted to validate these findings.

*Objective response **odds ratio ***statistical significance at alpha < 0.05