Seagen has reported positive topline data from the Phase III HER2CLIMB-02 clinical trial investigating Tukysa (tucatinib) in combination with the antibody-drug conjugate Kadcyla (ado-trastuzumab emtansine) in patients with previously treated HER2-positive metastatic breast cancer. 

In August 2023, Seagen announced that the primary endpoint of the trial of progression-free survival (PFS) has been met, however, the company did not release any data.  

Patients who received Tukysa and Kadcyla achieved a PFS of 9.5 months compared to 7.4 months in the placebo and Kadcyla alone cohorts. Patients with brain metastasis had a PFS of 7.8 months compared to 5.7 months in patients in the placebo arm. 

Overall survival data, which is the secondary endpoint, has not yet matured, as per a 6 December press release.  

The multicentre, randomised, double-blind trial enrolled 565 patients who had had prior treatment with taxane and trastuzumab. 

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By GlobalData

In the announcement accompanying the data, lead study author Sara Hurvitz said: “Combining HER2-directed therapies can improve outcomes for people with locally advanced or metastatic HER2-positive breast cancer. Notably, the HER2CLIMB-02 trial is the second randomised study including patients with brain metastasis demonstrating that Tukysa delays disease progression in this population.” 

Tukysa is a tyrosine kinase inhibitor of HER2 and first gained approval by the US Food and Drug Administration (FDA) in April 2020 to treat adult patients with advanced unresectable or metastatic HER2-positive breast cancer, including patients with brain metastases, who have received one or more prior anti-HER2-based regimens in the metastatic setting. Merck (MSD) has exclusive rights to commercialise Tukysa in regions outside of the US, Canada, and Europe. 

Last year, Tukysa generated $353m in sales, as per Seagen’s 2022 financial results. According to GlobalData’s Pharma Intelligence Center, Tukysa is forecasted to generate $1.6bn in sales in 2029. 

GlobalData is the parent company of Clinical Trials Arena. 

Seagen is also investigating Tukysa as a treatment for colorectal cancer in the Phase III MOUNTAINEER-03 trial (NCT05253651). The trial plans to enrol 400 patients and has a primary completion date of July 2025. The open-label, randomised study evaluates Tukysa with trastuzumab and MFOLFOX6 versus standard-of-care treatment in first-line HER2+ metastatic colorectal cancer. The primary endpoint of the study is PFS.