Activity of tucatinib plus trastuzumab in metastatic colorectal cancer

In patients with chemotherapy-refractory, HER2-positive, RAS wild-type unresectable or metastatic colorectal cancer, the combination of tucatinib plus trastuzumab has a promising activity, as shown by the latest results of the MOUNTAINEER trial recently published in The Lancet Oncology.

The MOUNTAINEER trial is a global, open-label, phase 2 study that enrolled adult patients with chemotherapy-refractory, HER2-positive, RAS wild-type unresectable or metastatic colorectal cancer at 34 sites in five countries. The trial was designed as a single-cohort study with an expansion and 117 patients were given tucatinib (300 mg orally twice daily) plus intravenous trastuzumab (8 mg/kg as an initial loading dose, then 6 mg/kg every 21 days, cohort A) for the duration of treatment until progression; after expansion, patients were randomly assigned to either tucatinib plus trastuzumab (cohort B) or tucatinib monotherapy (cohort C). The overall response rate, which was the primary outcome for the evaluated population, was 38% in the later lines. The duration of response was over a year and the progression-free survival was around 8 months; the most common adverse event was diarrhea for all the cohorts, with discontinuation rates of 6%; all deaths in treated patients were due to disease progression. «Tucatinib plus trastuzumab had clinically meaningful anti-tumor activity and favorable tolerability. This treatment is the first US Food and Drug Administration-approved anti-HER2 regimen for metastatic colorectal cancer and is an important new treatment option for chemotherapy-refractory HER2-positive metastatic colorectal cancer», authors conclude.