Daiichi Sankyo and AstraZeneca have dosed the first subject in a Phase III DESTINY‑Breast09 trial of Enhertu (trastuzumab deruxtecan) with or without pertuzumab.

The trial will evaluate the treatment as a potential first-line therapy for human epidermal growth factor receptor 2 (HER2) positive metastatic breast cancer patients.

Designed with Daiichi Sankyo’s DXd ADC technology, Enhertu is a HER2-directed antibody-drug conjugate.

The global head-to-head Phase III DESTINY-Breast09 trial is assessing the safety and efficacy of Enhertu 5.4mg/kg with or without pertuzumab versus standard of care.

It will enrol a total of 1,134 subjects at various centres across Africa, Asia, Europe, North America, Oceania, and South America.

Subjects will be randomised in a 1:1:1 ratio to be treated with either Enhertu monotherapy with a pertuzumab‑matching placebo or Enhertu plus pertuzumab, or the current standard of care treatment with docetaxel or paclitaxel, trastuzumab and pertuzumab.

Progression-free survival (PFS) will be the trial’s primary goal. Investigator-assessed PFS, overall survival, objective response rate, duration of response, immunogenicity, pharmacokinetics, and safety will be analysed as some of the secondary goals.

Daiichi Sankyo noted that DESTINY-Breast09 is the first study of Enhertu in the first-line metastatic setting in HER2 positive breast cancer patients.

Daiichi Sankyo Oncology R&D oncology development senior vice-president and global head Gilles Gallant said: “Based on the encouraging results we are seeing in patients who have received prior treatment for HER2 positive metastatic breast cancer, we have initiated DESTINY-Breast09 to evaluate whether earlier use of Enhertu alone or as part of a novel combination regimen may help improve outcomes for patients in the first-line metastatic setting as compared to the current standard of care.”

In March 2019, Daiichi Sankyo and AstraZeneca signed a global partnership deal worth up to $6.9bn to co-develop and co-market Enhertu.

Meanwhile, Daiichi Sankyo announced that the company will discontinue the development of nafamostat inhalation formulation, DS-2319, for Covid-19 treatment in Japan.

DS-2319, which contains nafamostat mesylate, entered a Phase I Covid-19 trial in March.

The company decided to discontinue DS-2319’s development in this indication based on findings from non-clinical studies and the Phase I trial.