Background: The MET receptor tyrosine kinase is implicated in tumor cell proliferation, invasion, and metastasis, and is activated in NRAS mutant melanoma. Tivantinib is an oral, selective MET inhibitor currently in phase II/III clinical trials. Tivantinib plus sorafenib exhibited synergistic antitumor activity vs single-agent activity in several tumor models. 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. Dose escalation previously established the RP2D as tivantinib 360 mg twice daily (BID) plus sorafenib 400 mg BID. Extension cohorts enrolled ≤ 20 pts each with melanoma or other tumors. Pts were treated until disease progression or unacceptable toxicity. Results: 16 pts with melanoma (median age, 66 yr) received treatment at the RP2D, and 3 pts are still on study. 12 pts received ≥ 1 previous systemic anticancer treatment (median, 1.2; range, 0-5) including ipilimumab (2 pts) or MEK inhibitor (1 pt). Common adverse events (≥ 25%) were rash (50%), diarrhea and fatigue (44% each), anorexia (38%), stomatitis and nausea (31% each), and anemia, weight decrease, and hypophosphatemia (25% each). Best responses were complete response (CR) in 1 pt, partial response (PR) in 3 pts, and stable disease (SD) in 3 pts. 4 pts had progressive disease and 5 pts were not evaluable (3 pts had not reached first assessment time, 1 pt withdrew consent, and 1 pt had unacceptable toxicity). The overall response rate and disease control rate were 25% and 44%, respectively. Median progression-free survival (mPFS) was 5.3 mo (95% CI, 1.6-12.9 mo). Among 8 pts with NRAS mutations, mPFS was 9.2 mo (95% CI, 5.3-12.9 mo) and responses were 1 CR, 1 PR, and 2 SD. Conclusions: Tivantinib plus sorafenib combination therapy was well tolerated and exhibited preliminary anticancer activity in pts with melanoma. Dual inhibition of MET and angiogenesis may be an effective treatment strategy in NRAS-mutant melanoma.