Background: Surufatinib (S) is a targeted inhibitor of tyrosine kinases VEGFR1, 2, and 3; FGFR1; and CSF-1R. A manageable safety profile and statistically significant efficacy of S have previously been demonstrated in patients (pts) with advanced NETs of extrapancreatic (epNET) and pancreatic (pNET) origin in 2 phase 3 randomized trials conducted in China (SANET-ep, NCT02588170; SANET-p, NCT02589821). Pts with epNETs achieved a median progression free survival (PFS) of 9.2 v 3.8 months (mo) (hazard ratio [HR] 0.334; p < 0.0001), and pts with pNETs achieved a median PFS of 10.9 v 3.7 mo (HR 0.491; p = 0.0011), with S v placebo, respectively. S has recently been approved for the treatment (tx) of pts with epNETs in China. Methods: A phase 1, dose escalation (ESC)/expansion (EXP) trial was conducted to evaluate and confirm the efficacy and safety of S in US pts. ESC was completed, and the maximum tolerated dose and recommend phase 2 dose were determined to be 300 mg, same as previous trials. The EXP completed enrollment of the epNET and pNET cohorts, and the primary endpoint was investigator-assessed PFS rate at 11 mo. Secondary objectives included assessment of safety and PK. Results: 32 pts with heavily pretreated progressive NETs (16 epNET and pNET each) were enrolled in the dose EXP. The median age was 62.2 years (44-75) and 64.4 years (39-72) for epNET and pNET pts, respectively. 65.6% of pts received ≥3 prior lines of tx (median lines of therapy: epNET: 2 [2-5]; pNET: 4 [1-8]), and all pts previously received everolimus and/or sunitinib. As of the data cutoff of 30-Jun-20, 7 pts remained on tx (4 epNET; 3 pNET). The median number of tx cycles was 8.0 (2, 15) for epNET and 8.5 (2, 23) for pNET pts. The PFS rate at 11 mo was 51.1% (95% confidence interval [CI]: 12.8, 80.3) for pts with epNETs and 57.4% (95% CI: 28.7, 78.2) for pts with pNETs. The observed mPFS was 11.50 mo (95% CI: 6.47, 11.50) and 15.18 mo (95% CI: 5.19, NR) for pts with epNETs and pNETs, respectively. An objective response rate (ORR) of 6.3% was observed for pts with epNETs and 18.8% for pts with pNETs. A disease control rate of 90.6% (95% CI: 75.0, 98.0) was observed for all NET pts (93.8% epNET; 87.5% pNET). The safety profile of S remains consistent with previously completed trials. All pts (n = 32) had reported at least 1 adverse event (AE), and 24 pts (75%) reported AEs ≥grade 3. The most common AEs of any grade reported were fatigue (46.9%), hypertension (43.8%), proteinuria (37.5%), diarrhea (34.4%), vomiting (28.1%), and nausea (25.0%). The most commonly reported AEs ≥grade 3 ( > 5%) were hypertension (37.5%); diarrhea (9.4%); and proteinuria, dysphagia, and anemia (6.3% each). AEs leading to tx discontinuation occurred in 21.9% of pts. Conclusions: S has demonstrated antitumor activity in heavily pretreated US pts with progressive NETs with a manageable safety profile that is consistent with 2 completed phase 3 studies. S continues to be studied in other ongoing clinical trials globally. Clinical trial information: NCT02549937