Background: The multi-kinase inhibitor regorafenib (REGO) and oral fluoropyrimidine TAS-102 (TAS) show efficacies as single agents in treatment of refractory metastatic CRC patients (pts). We conducted a conventional 3+3 dose finding to determine a recommended phase II dose (RP2D) of its combination REGOTAS and efficacy in 3-4.-line. Methods: Eligible patients with ECOG 0-1, measurable mCRC, not amenable to surgery had at least 3rd-line treatments. Prior fluoropyrimidine-based and anti-VEGF (R) combinations were mandatory, and anti-EGFR for RAS WT tumors. TAS was given on days 1-5 and 8-12 (28-days cycle); REGO on days 2-22 (dose levels see table below). The following major AE categories were used to define DLTs if they occurred during the first 2 treatment cycles: any grade ≥3 non-hematologic toxicity (except vomiting, nausea, non-significant lab abnormalities), grade ≥3 hematological toxicities, grade ≥3 bleeding. Tumor response was assessed Q8W as per RECIST1.1. EudraCT 2016-001968-11; NCT03305913. Results: All observed toxicities were consistent with safety profile of individual IMPs. 6 pts were enrolled into each DL1 and DL2 (n=12 in total). One DLT was observed in 1/6 pts in DL1; 2 DLTs in 2/6 pts in DL2. All DLTs were only grade 3 hypertension was well manageable, causality was attributed to REGO. No DLT resulted in treatment discontinuation. Results indicate a RP2D of 25mg/m² TAS-102 BID + 120mg REGO daily. No remissions were observed. Overall disease control rate (DCR) after 8 weeks was promising with 58.3% (DCR of 33.3% for DL1 and 83.3% in DL2) and remarkably better as historical data with 41/44% for REGO/TAS102 alone, respectively (Lancet 2013/NEJM 2015). Conclusions: Toxicities of REGOTAS were consistent with safety profiles of REGO and TAS alone. No additional DLTs were attributed to REGOTAS. Thus, the risk-benefit assessment of REGOTAS was positive. DCR was clinically quite meaningful. Mature PFS and OS will be presented at the meeting. Clinical trial information: NCT03305913