Design and Goals of the Phase 3 MOUNTAINEER-03 Study in mCRC

Tanios S. Bekaii-Saab, MD, FACP, medical oncologist, medical director, Cancer Clinical Research Office, vice chair and section chief, medical oncology, Department of Internal Medicine, Mayo Clinic, Phoenix, Arizona, discusses the patient population, methods, and design utilized in the phase 3 MOUNTAINEER-03 study (NCT05253651).

In the global, open label, randomized, study, investigators seeks to evaluate tucatinib (Tukysa), trastuzumab (Herceptin), and 5-fluorouracil, leucovorin, and oxaliplatin (mFOLFOX6) compared with the standard-of-care treatment for patients with frontline HER2-positive metastatic colorectal cancer.

The primary end point assessed in the trial is progression-free survival per RECIST v1.1 with secondary end points of overall survival and confirmed objective response.

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0:08 | At a high level, MOUNTAINEER-03 is a global, randomized, open-label, phase 3 trial. It is the largest ever phase 3 trial or trial in HER2-positive metastatic colorectal cancer. This will take first-line patients with metastatic colorectal cancer and they will be assessed for HER2-positivity centrally. They have to be RAS wild-type since we know the RAS-mutated tumors don’t respond as well. Patients will be randomized to tucatinib, trastuzumab, and chemotherapy vs FOLFOX6 plus/minus the biologic of choice.

1:00 | The primary end point of the study is progression-free survival and the reason for this is that we expect tucatinib and trastuzumab, or other targeted therapies, to be available, so patients who may not have received them in the earlier cycle can cross over to them. It will make it very difficult to assess survival as the primary end point, although we still hope that survival is superior with moving those agents sooner rather than using them later. [Overall survival will] be essentially a secondary end point.

1:33 | This study will need to accrue about 400 patients. It’s a major lift for a rare patient population, but that is what we’re excited about. MOUNTAINEER-03 is a global, randomized, phase 3 study that will hopefully move HER2 targeted therapies into the first-line.