The response was seen in the highest dose group in the continuing Phase1/2a dose-escalation trial, said Harpoon.
In addition, three of seven patients enrolled in the currently highest fixed-dose cohort had serum PSA reductions, including one with a reduction of 50%.
Gerald McMahon, Harpoon Therapeutics’ chief executive, said: “We are excited to report our first confirmed partial response in the continuing dose-escalation trial for HPN424, especially in a heavily pretreated patient population with advanced metastatic disease.”
In other ongoing trials, Harpoon said dose escalation is continuing in the HPN536 Phase 1/2a clinical trial for the treatment of ovarian cancer and and in the HPN217 Phase 1/2 clinical trial for multiple myeloma.
Harpoon expects to report initial data readouts from both of these trials in 2021.
In addition, Harpoon expects that dosing of the first patient in the Phase 1/2 trial for HPN328, in small cell lung cancer and other DLL3- associated tumours, will occur by the end of the year.
“We are also excited by the potential for multiple data releases in 2021 on all four of our programs, which we believe represent meaningful milestones for our company,” McMahon added.