Background Pexidartinib, a novel, orally administered small-molecule tyrosine 
kinase inhibitor, has strong selectivity against colony-stimulating factor 1 
receptor. This phase I, nonrandomized, open-label multiple-dose study evaluated 
pexidartinib safety and efficacy in Asian patients with symptomatic, advanced 
solid tumors. Materials and Methods Patients received pexidartinib: cohort 1, 
600 mg/d; cohort 2, 1000 mg/d for 2 weeks, then 800 mg/d. Primary objectives 
assessed pexidartinib safety and tolerability, and determined the recommended 
phase 2 dose; secondary objectives evaluated efficacy and pharmacokinetic 
profile. Results All 11 patients (6 males, 5 females; median age 64, range 
23-82; cohort 1 n = 3; cohort 2 n = 8) experienced at least one 
treatment-emergent adverse event; 5 experienced at least one grade ≥ 3 adverse 
event, most commonly (18%) for each of the following: increased aspartate 
aminotransferase, blood alkaline phosphatase, gamma-glutamyl transferase, and 
anemia. Recommended phase 2 dose was 1000 mg/d for 2 weeks and 800 mg/d 
thereafter. Pexidartinib exposure, area under the plasma concentration-time 
curve from zero to 8 h (AUC0-8h), and maximum observed plasma concentration 
(Cmax) increased on days 1 and 15 with increasing pexidartinib doses, and time 
at Cmax (Tmax) was consistent throughout all doses. Pexidartinib exposure and 
plasma levels of adiponectin and colony-stimulating factor 1 increased following 
multiple daily pexidartinib administrations. One patient (13%) with tenosynovial 
giant cell tumor showed objective tumor response. Conclusions This was the first 
study to evaluate pexidartinib in Asian patients with advanced solid tumors. 
Pexidartinib was safe and tolerable in this population at the recommended phase 
2 dose previously determined for Western patients (funded by Daiichi Sankyo; 
clinicaltrials.gov number, NCT02734433).