Background: SWITCH, a prospective, randomized sequential trial to evaluate SU/SO versus SO/SU, revealed no difference in first-line or total PFS or OS, but no direct comparison was obtained between 1st line sunitinib (SU) and sorafenib (SO) for clear cell (CC) metastatic renal cell carcinoma (mRCC). Methods: Treatment-naïve patients with CC mRCC, ECOG PS 0/1 and MSKCC favorable or intermediate risk were randomized to receive open-label SU/SO or SO/SU at the standard dosage and schedule. The primary endpoint was 1st line PFS, and secondary endpoints were total PFS and OS. The calculated sample size was 59 per group, with α = 0.05, β = 0.10, and a censoring rate of 15%. Results: Of 124 patients enrolled in this study from February 2010 to July 2012 from 39 institutions, 120 could be evaluated (SU/SO, 57 and SO/SU, 63). Baseline patients' characteristics in the SU/SO and SO/SU groups were as follows: favorable risk, 21% and 22%; and presence ofnephrectomy, 88% and 89%, respectively. First-line mPFS was 8.7 and 7.0 months in the SU/SO and SO/SU groups, respectively (HR, 0.67; 95% CI, 0.42–1.08; p= 0.095). There was no statistically significant difference in total (T)-PFS, 27.8 M, and 22.6 m (HR 0.73, CI 0.428-1.246; p=0.247), or OS 38.4 m and 30.9 m (HR 0.934, CI 0.588-1.485; p=0.773). Subgroup analyses showed that T-PFS was NR and 27.8 m (p=0.021) in the favorable risk, and 38.4 m and 16.1 m (p=0.009) in with less than 5 metastatic sites, 6.5 m and 13.6 m (p=0.025) without nephrectomy in the SU/SO and SO/SU groups, respectively. The most common adverse events (AEs) in case of first-line SU or SO (all grade, all cause) were hand–foot syndrome (71% vs. 86%), hypothyroidism (70% vs. 33%), fatigue (57% vs. 40%), hypertension (55% vs. 44%), and diarrhea (23% vs. 38%). AEs were generally lower during second-line therapy. Conclusions: There was no significant difference in first-line PFS, T-PFS, and OS between the two sequential treatments. Although fewer patients received second-line treatment in the SU/SO group, OS in this group was numerically longer than that in the SO/SU group. Clinical trial information: 01481870.