A Study of Pimitespib in Combination With Imatinib in Patients With GIST (CHAPTER-GIST-101)

A Phase 1 Study of TAS-116 (Pimitespib) in Combination With Imatinib in Patients With Advanced Gastrointestinal Stromal Tumor

This study consists of Dose escalation part and Expansion part. In Dose Escalation Part, the maximum tolerated dose of combination of pimitespib and imatinib in patients with gastrointestinal stromal tumors (GIST) who are judged to be refractory to imatinib, estimate the recommended dose, evaluate safety and pharmacokinetics, and observe the antitumor effect. Expansion part consists of 3 arms. In Arm A, the efficacy and safety will be evaluated, which of the combination of pimitespib and imatinib in patients with GIST who have failed imatinib at doses below the MTD determined in Dose Escalation Part. In Arm B, the efficacy and safety of pimitespib monotherapy will be evaluated and the therapeutic effect of imatinib administration after pimitespib will be evaluated in an exploratory manner. In Arm C, the efficacy and safety of sunitinib monotherapy will be evaluated as reference data.

Pimitespib will be administered orally in 5 consecutive days followed by 2 days off treatment (QD 5) on an empty stomach at least 1 hour before or 2 hours after a meal. The doses in the Dose Escalation Part will be 80, 120 (starting dose), and 160 mg. The doses used in Arm A will be MTD or recommended dose (RD) based on the information, including the safety and the pharmacokinetics (PK) data in the Dose Escalation Part. In Expansion Part-B, pimitespib will be administered with the starting dose of 160 mg daily.

Imatinib will be administered orally, after a meal and large glass of water QD. The doses in Dose Escalation Part will be 400 mg or 300 mg (De-escalation). The doses used in Expansion Part-A will be MTD or RD based on information, including the safety and PK data in the Dose Escalation Part. In Expansion Part-B, imatinib will be administered post after pimitespib discontinuation with the starting dose of 400 mg daily.

Sunitinib will be administered orally QD with a starting dose of 50 mg, on a schedule of 4 weeks on treatment followed by 2 weeks off, and will be taken with or without a meal in Expansion Part-C.

Inclusion Criteria: Provided written informed consent Histologically confirmed GIST Progressed on the basis of imaging during or within 6 months of the last imatinib administration at enrollment Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 Exclusion Criteria: Received treatment with any other line of therapy besides imatinib for advanced GIST; including local surgery and radiotherapy A serious illness or medical condition Previous or concurrent cancer that is distinct in primary disease or histology from cancer that is being evaluated in this study Pregnancy or lactation (including lactation interruption)

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