New Clinical Data for Zanidatamab in HER2+ /HR+ Metastatic Breast Cancer Presented Today at 2022 SABCS

Zymeworks Inc. (NYSE: ZYME), a clinical-stage biopharmaceutical company developing multifunctional biotherapeutics, today presented new clinical data for zanidatamab, the company’s investigational HER2-targeted bispecific antibody, in combination with palbociclib, a CDK4/6 inhibitor, and fulvestrant, a selective estrogen receptor degrader, in patients with heavily pretreated HER2-positive hormone-receptor positive metastatic breast cancer. The data were presented today in a spotlight poster session entitled Treatment of HER2-positive (HER2+) hormone-receptor positive (HR+) metastatic breast cancer (mBC) with the novel combination of zanidatamab, palbociclib, and fulvestrant during the San Antonio Breast Cancer Symposium (SABCS) taking place in San Antonio, Texas and virtually.

Clinical Data Highlights

The data presented at SABCS are from a clinical study of 45 patients with heavily pretreated HER2-positive HR-positive metastatic breast cancer who received zanidatamab in combination with palbociclib and fulvestrant. Patients had received prior regimens containing HER2-targeted agents including trastuzumab (100%), pertuzumab (80%), T-DM1 (98%), and other available options.

In 36 efficacy-evaluable patients, treatment with zanidatamab in combination with palbociclib and fulvestrant resulted in a cORR of 33% and DCR of 92%, and the majority of patients experienced a decrease in tumor size. The mPFS was 9.6 months with seven patients still on study at the time of data cutoff (August 31, 2022). The regimen was generally well-tolerated, with the majority of treatment-related adverse events considered mild to moderate in severity (Grade 1 or 2).

“Zanidatamab together with palbociclib and fulvestrant shows encouraging antitumor activity and a manageable tolerability profile in patients with HER2‑positive hormone-receptor positive breast cancer that has progressed after treatment with multiple HER2-targeted agents,” said Neil Josephson, M.D., Chief Medical Officer at Zymeworks. “We are encouraged by the durability of disease control and median progression-free survival in this heavily pretreated patient population indicating that this regimen has the potential to be developed as a chemotherapy-free treatment option for these patients.”