Background: SURTIME compared immediate CN followed by sunitinib 50mg/day (4/2 weeks on-off) 4 weeks after surgery (n=50) versus 3 cycles sunitinib followed by CN in the absence of progression and continued sunitinib 4 weeks after surgery (n=49). In the intention to treat analysis, the hazard ratio of the secondary endpoint overall survival (OS) favored deferred CN [0.57 (CI: 0.34–0.95, p=0.032)] with a median OS of 32.4 (CI: 14.5-65.3) versus only 15.0 months (CI: 9.3–29.5), following immediate CN. We investigated differences in exposure to systemic therapy between the two arms. Methods: Post-hoc exploratory analysis of number of patients receiving sunitinib, overall response rate (ORR) by RECIST 1.1, length of drug exposure and dose intensity in the immediate and deferred arm. Descriptive methods and 95% confidence intervals (CI) were used. Results: In the deferred arm, 97.7% (CI: 89.3-99.6; n=48) received sunitinib versus only 80% (CI: 66.9-88.7, n=40) in the immediate arm. Following immediate CN, 19.6% had confirmed progression at an interval CT scan 4 weeks after CN compared to baseline and 25% started with sunitinib > 4 weeks after surgery. At week 16, 46.0% had progressed at metastatic sites in the immediate CN arm versus 32.7% in the deferred arm, who had a per-protocol recommendation against nephrectomy. In the deferred arm, 83% completed 3 cycles sunitinib with 77.1% at >90%-120% relative dose intensity and an ORR of 29%, reducing the median sum of target lesions from 162 to 127 mm prior to planned CN.Of the patients who started with sunitinib in the immediate (n=40) or continued in the deferred arm after CN (n=29) median duration of treatment was 140 versus 351 days. Conclusions: With immediate CN fewer patients receive systemic therapy, which is administered later and shorter compared to the deferred approach. Starting systemic therapy with sunitinib leads to early and more profound control of the disease and identification of progression prior to planned CN which may translate into the observed survival benefit. Clinical trial information: NCT01099423