- Studies suggested the existence of a 'trial effect', in which for a given treatment, participation in a clinical trial is associated with a better outcome. Sunitinib is a standard treatment for metastatic renal cell carcinoma (mRCC). We aimed to study the effect of clinical trial participation on the outcome of mRCC patients treated with sunitinib, which at present, is poorly defined. The records of mRCC patients treated with sunitinib between 2004-2013 in 7 centers across 2 countries were reviewed. We compared the response rate (RR), progression free survival (PFS), and overall survival (OS), between clinical trial participants (n=49) and a matched cohort of non-participants (n=49) who received standard therapy. Each clinical trial participant was individually matched with a non participant by clinicopathologic factors. PFS and OS were determined by Cox regression. The groups were matched by age (median 64), gender (male 67%), Heng risk (favorable 25%, intermediate 59%, poor 16%), prior nephrectomy (92%), RCC histology (clear cell 86%), pre-treatment NLR (>3 in 55%, n=27), sunitinib induced hypertension (45%), and sunitinib dose reduction/treatment interruption (41%). In clinical trial participants versus non-participants, RR was partial response/stable disease 80% (n=39) versus 74% (n=36), and progressive disease 20% (n=10) versus 26% (n=13) (p=0.63, OR 1.2). The median PFS was 10 versus 11 months (HR=0.96, p=0.84), and the median OS 23 versus 24 months (HR=0.97, p=0.89). s In mRCC patients treated with sunitinib, the outcome of clinical trial participants was similar to that of non-participants who received standard therapy.