Biopharmaceutical company Zymeworks Inc (NYSE:ZYME) revealed on Saturday an agreement with Pfizer for the planned launch of a Phase 2 trial evaluating ZW25 combination therapy for treating people with advanced HER2-positive, HR-positive breast cancer.

Breast cancer occurs when cells of the breast grow uncontrollably. About 15 to 20% of all breast cancers are positive for human epidermal growth factor receptor 2, or HER2.

Under the terms of the agreement, Zymeworks will sponsor the study and Pfizer will provide palbociclib.

As part of the agreement, Zymeworks' HER2-targeted bispecific antibody ZW25 is being evaluated in combination with Pfizer's Ibrance (palbociclib), an oral CDK4/6 inhibitor, and the hormone therapy fulvestrant in patients with previously-treated locally advanced and/or metastatic HER2-positive, HR-positive breast cancer.

ZW25 is a bispecific antibody based on Zymeworks' Azymetric platform that can simultaneously bind two non-overlapping epitopes of HER2, known as biparatopic binding. This design results in multiple mechanisms of action including dual HER2 signal blockade, increased binding and removal of HER2 protein from the cell surface and potent effector function leading to encouraging anti-tumor activity.

This Phase 2 clinical trial is a multicenter, open-label, two-part study conducted by the partnership. Part one of the study will evaluate the safety and tolerability of ZW25 in combination with palbociclib and fulvestrant and identify the recommended doses (RD) of ZW25 and palbociclib. Part two of the study will evaluate anti-tumor activity at the RD level. The trial will enroll up to 76 patients at sites in the US and Canada and expand into Spain.