So in the presentation at ASCO this year, we present data on patritumab deruxtecan, or also known as HER3-DxD, which is a HER3 antibody drug conjugate, specifically being studied in patients with EGFR mutant lung cancer who have develop resistance to EGFR inhibitors. And the rationale for the study comes from the fact that the vast majority of EGFR mutant cancers also tend to express HER3, which is another ErbB family member. But HER3 is not a known resistance mechanism to EGFR inhibitors. And as such, is a potential novel therapeutic target for this subset of lung cancer.
So in the study, we evaluated HER3-DxD in this phase I study in an expansive cohort, in patients that had failed prior EGFR inhibitors. And observed a response rate, a confirmed response rate of 39% and a median progression free survival of 8.2 months. This was a fairly heavily pretreated group of individuals. And as such, we're encouraged by the clinical data.
On the correlative science front, we also looked at the patients with different resistance mechanisms to EGFR inhibitors. And as predicted from the mechanism, we did we saw a broad range of activity regardless of the specific resistance mechanism. Whether it was an EGFR mutation, a bypass signaling pathway, or whether it was somebody who did not have an identifiable resistance mechanism, we still saw activity. So I think it opens up the possibility of using HER3-DxD as a mechanism agnostic strategy to treat patients that have developed resistance to prior EGFR inhibitors.
The next steps in this study are to perform additional studies. There's an additional cohort that has completed enrollment. And we await data on that, as well
There is an ongoing phase II trial evaluating single agent HER3-DxD in patients that have failed prior osimertinib and the systemic chemotherapy. And there's also a phase I clinical trial that has also started, combining osimertinib and HER3-DxD, specifically being evaluated in patients who have just been treated with first line osimertinib. So we hope that this will be a new and novel approach to treat patients' cancers that have developed resistance to EGFR inhibitors.