Seagen has reported full data from the pivotal Phase II MOUNTAINEER clinical trial, where Tukysa (tucatinib) plus trastuzumab was found to be well-tolerated with lasting responses in previously treated HER2-positive metastatic colorectal cancer (mCRC) patients.

An oral therapy, Tukysa is a tyrosine kinase inhibitor of the HER2 protein.

The US and European open-label, multicentre, randomised trial analysed tucatinib plus trastuzumab or as a monotherapy.

It enrolled 117 HER2-positive metastatic or unresectable colorectal cancer patients who had received standard-of-care treatments earlier.

According to the findings, HER2-positive patients who received tucatinib plus trastuzumab had a confirmed objective response rate (cORR) of 38.1% as per blinded independent central review (BICR) at a median follow-up duration of 20.7 months.

The median duration of response (DoR) per BICR was reported to be 12.4 months in these subjects.

Furthermore, median progression-free survival per BICR and median overall survival were observed to be 8.2 and 24.1 months, respectively.

The ORR per BICR by 12 weeks in cohort of subjects who were treated with tucatinib monotherapy was reported to be 3.3% while the disease control rate was 80%.

Diarrhea, fatigue, nausea and infusion-linked reaction were reported to be the most common treatment-emergent adverse events (AEs) in subjects who received tucatinib and trastuzumab.

Based on the trial results, the company plans to file a supplemental New Drug Application with the US Food and Drug Administration under the Accelerated Approval Program.

Seagen interim CEO and chief medical officer Roger Dansey said: “This study has shown the benefits of dual-HER2 inhibition with tucatinib and trastuzumab in patients with HER2-positive metastatic colorectal cancer, including many whose cancer had spread to the liver or lungs before joining the trial.

“We believe this chemotherapy-free combination may play an important role in addressing the unmet needs of patients with this disease.”