The study is designed as a 2-part, multicenter, open-label, Phase 1, dose-escalation, cohort-expansion study of KHK2455 as a monotherapy run-in (Cycle 0) followed by combination therapy with the anti-CCR4 antibody mogamulizumab (Cycle 1 and beyond).~Part 1 will identify the MTD or the highest protocol-defined dose, in the absence of exceeding the MTD, for the KHK2455 monotherapy run-in and for the combination regimen (KHK2455 monotherapy [Cycle 0] followed by KHK2455 + mogamulizumab combination [Cycle 1]). The dose escalation phase (Part 1) will enroll up to approximately 36 subjects.~Part 2, the cohort-expansion phase, will further explore the safety, tolerability, PK, PD, pharmacogenomics (PGx), and preliminary anti-tumor activity of KHK2455 administered as monotherapy and in combination with mogamulizumab in subjects with one cohort-specific tumor type. In Part 2, approximately 15 subjects with a selected tumor type will be enrolled and treated with the recommended KHK2455 dose established in Part 1 in combination with mogamulizumab.
The purpose of this study is to characterize the safety, tolerability, and determine the maximum tolerated dose (MTD) or the highest protocol-defined dose, in the absence of exceeding the MTD, of KHK2455 administered orally in combination with mogamulizumab to subjects with locally advanced or metastatic solid tumors.