Background: Inhibitors of vascular endothelial growth factor (VEGF) and VEGF receptor are standard therapy for RCC, and the MET signaling pathway is implicated in tumor angiogenesis. Tivantinib is an oral, selective MET inhibitor. In several tumor models, tivantinib plus sorafenib exhibited synergistic antitumor activity vs single-agent activity. This phase I dose-escalation study assessed the safety of tivantinib plus sorafenib in pts with advanced solid tumors. Methods: Endpoints were safety, the recommended phase II dose (RP2D) of tivantinib plus sorafenib, and antitumor activity. Previously, dose escalation established the RP2D as tivantinib 360 mg twice daily (BID) plus sorafenib 400 mg BID. Extension cohorts enrolled ≤ 20 pts each with RCC or other tumors. Patients were treated until disease progression or unacceptable toxicity. Results: 20 pts (mean age, 60 yr) including 16 clear cell, 3 papillary, and 1 clear cell/chromophobe RCC pts received treatment at the RP2D (n = 19) or tivantinib 360 mg BID plus sorafenib 200 mg BID (n = 1). 4 pts are still on study. 16 pts (13 with clear cell RCC) received ≥ 1 previous systemic therapy (median, 2; range, 0-4) including VEGF (14 pts) and/or mTOR (5 pts) inhibitors. The most common (≥ 25%) adverse events were rash (65%), diarrhea (45%), alopecia (40%), hypophosphatemia (35%), and fatigue, stomatitis, palmar-plantar erythrodysesthesia syndrome, and pruritus (25% each). Best response was partial response (PR) in 3 pts (all clear cell RCC pts) and stable disease (SD) in 15 pts (11 clear cell, 3 papillary, and 1 clear cell/chromophobe RCC pts). 7 pts with SD had ≥ 10% tumor size reduction. The overall response rate (ORR) and disease control rate (DCR; PR + SD) were 15% and 90%, respectively. Median progression-free survival (mPFS) was 12.7 mo (95% CI, 7.1-14.5 mo). In 14 pts previously treated with a VEGF inhibitor, best response was 2 PR and 10 SD, the ORR and DCR were 14% and 86%, respectively, and mPFS was 12.7 mo (95% CI, 5.3-NR mo). Conclusions: Oral combination therapy with tivantinib plus sorafenib was well tolerated and exhibited preliminary anticancer activity in pts with RCC, including pts pretreated with VEGF inhibitors.