Background: KBP-5209 is a novel potent and irreversible inhibitor of tyrosine kinases of the human epidermal growth factor receptor (EGFR) family that preclinically has demonstrated potent antitumor activities in esophageal and gastric cancers and NSCLC. Methods: This first-in-human study (NCT02442414) was conducted to determine tolerability, safety, pharmacokinetics and antitumor activity of KBP-5209 administered QD or BID in patients (pts) with advanced solid tumors. Dose escalation (DE) initially was based on a modified accelerated titration plan and then shifted to a standard 3+3 design. The starting dose was 20 mg QD. Eligible patients were adults with advanced, refractory solid tumors with ECOG PS < 1. A cycle was 28 days. DLTs were evaluated for during the first cycle. DE enriched for patients with tumors having molecular alterations in EGFR or HER2/3. Dose escalation continues so dose expansion has not initiated. Results: As of 26 Nov, 2016, 23 pts (15 females, 8 males) are a part of the evaluable population with a median age 57 (37-79) treated at doses of 20mg (1), 40mg (3), 60mg (7), 70mg (4), 80mg (6) QD and 20mg BID (2).Tumor types included breast (6), CRC (4), ovarian (3), H&N (2), sarcoma (2), and NSCLC, sinus, gastric, gallbladder, pancreas, CUP tumor (1 each). Tumor genetic profiles were available for 20 pts. DLTs were G3 diarrhea, nausea, and vomiting, which occurred in 1 pt at 80mg QD and G3 Diarrhea, occurring in 1pt at 80mg QD. The most common adverse events related to study drug were diarrhea (60.9%), nausea (47.8%), vomiting (43.5%), fatigue (21.7%), decreased appetite (17.4%) and lipase increased (17.4%). Serious adverse events (SAEs) related to study drug were reported in 4pts: diarrhea (1 pt, 70mg QD; 1pt, 80mg QD), nausea and vomiting (1pt, 70mg QD), and diarrhea, nausea and vomiting (1 pt, 80mg QD). Stable disease has been observed in 7pts up to 24 weeks, in which 2/28 pts (7%) achieved tumor shrinkage. Conclusions: Based on the present data, KBP-5209 has been well tolerated with a safety profile similar to other pan-HER inhibitors. For QD dosing, maximum tolerated dose has been identified as 70mg QD. The BID dose escalation continues. Clinical trial information: NCT02442414