MOUNTAINEER-02 : A Randomized, Double-blind, Placebo-controlled, Active Comparator Phase 2/3 Study of Tucatinib in Combination With Trastuzumab, Ramucirumab, and Paclitaxel in Subjects With Previously Treated, Locally-advanced Unresectable or Metastatic HER2+ Gastric or Gastroesophageal Junction Adenocarcinoma (GEC)

Trial Identifiers

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• NCT04499924

Scientific Title

A Randomized, Double-blind, Placebo-controlled, Active Comparator Phase 2/3 Study of Tucatinib in Combination With Trastuzumab, Ramucirumab, and Paclitaxel in Subjects With Previously Treated, Locally-advanced Unresectable or Metastatic HER2+ Gastric or Gastroesophageal Junction Adenocarcinoma (GEC)

Commercial Sponsor

Seagen Inc.

Summary

In the Phase 2 part of the trial, participants and their doctors will know what drugs are being given (open-label). In the Phase 3 part, the study is "blinded." This means that participants, their doctor, and the study sponsor will not know which drugs are being given. Participants will be randomised into one of four arms. In the Phase 2 Arm (experimental), participants will receive tucatinib + trastuzumab + ramucirumab + paclitaxel. Tucatinib will be administered orally, twice daily at a dose of 300mg. Trastuzumab will be administered intravenously (via IV) at a dose of 6mg/kg on Cycle 1 Day 1, followed by 4mg/kg on Cycle 1 Day 15 and then Days 1 and 15 of each cycle thereafter. Ramucirumab will be administered via IV at a dose of 8mg/kg on Days 1 and 15 of each cycle. Paclitaxel will be administered via IV at a dose of 60 or 80mg/m^2 on Days 1, 8 and 15 of each cycle. In Phase 3 Arm A (experimental), participants will also receive tucatinib + trastuzumab + ramucirumab + paclitaxel, all administered the same as the Phase 2 Arm. In Phase 3 Arm B (active comparator), participants will receive Ramucirumab + paclitaxel + tucatinib placebo + trastuzumab placebo. Ramucirumab will be administered via IV at a dose of 8mg/kg on Days 1 and 15 of each cycle. Paclitaxel will be administered at a dose of 60 or 80mg/m^2 via IV on days 1, 8 and 15 of each cycle. The tucatinib placebo will be given twice daily, orally, and the trastuzumab placebo will be given via IV on Days 1 and 15 of each cycle. In Phase 3 Arm C (experimental), participants will receive Tucatinib + ramucirumab + paclitaxel + trastuzumab placebo. Tucatinib will be given twice daily, orally, at a dose of 300mg. Ramucirumab will be administered via IV at a dose of 8mg/kg on Days 1 and 15 of each cycle. Paclitaxel will be administered via IV at a dose of 60 or 80 on Days 1, 8 and 15 of each cycle. The Trastuzumab placebo will be given via IV on Days 1 and 15 of each cycle.