Next Steps for the MOUNTAINEER-03 Study in HER2+ Metastatic Colorectal Cancer

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, discusses what to expect if data from the MOUNTAINEER-03 study (NCT05253651) are positive.

The global, open label, randomized, phase 3 MOUNTAINEER-03 study is evaluating the combination of tucatinib (Tukysa), trastuzumab (Herceptin), and 5-Fluorouracil, leucovorin, and oxaliplatin (mFOLFOX6) as a first-line treatment for patients with HER2-positive metastatic colorectal cancer (CRC).

Investigators are assessing the primary end point is progression-free survival per RECIST v1.1, assessed by blinded independent central review, and the secondary end points of overall survival and confirmed objective response. If data from the trial end up being positive, this could lead to a new approval for the combination in the CRC space.

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0:08 | If MOUNTAINEER-03 is positive, it will essentially open the doors for global approval for tucatinib and trastuzumab added to FOLFOX6 in HER2-positive colorectal cancer. That's the first element that would come from this study. Following this, we need to start understanding, not from the study but if this ends up being positive and approved, then we [have to] start looking at those patients with lower expression of HER2. Those have not been included in most studies.

0:46 | We do have a study led by John Strickler, MD, that's going on through our research consortium that is looking at trastuzumab and tucatinib and added to TAS-102 in refractory patients [NCT05356897]. Those patients are who we expect to be of lower expression or have resistance mutations. [This study is to] hopefully understand more fully the role of adding those 2 agents to chemotherapy in patients who are less likely to respond just to the 2 agents.

1:22 | This could, if it shows signals, move into a larger study. Then, 1 of the points of interest is if we find the MOUNTAINEER-03 study to be positive, which we're hoping it ends up being positive and leads to a new standard in the metastatic setting, how can we then move this into the earlier stages?