Shares of Ambrx Biopharma (NYSE: AMAM) rocketed higher by more than 500% with more than 70 million shares traded during Friday's trading session.

The company reported preliminary safety and efficacy data from its Phase 2 ACE-Breast-03 study, which was presented at the San Antonio Breast Cancer Symposium.

Ambrx's Phase 2, multicenter study of ARX788 was conducted in the US, Korea and Australia and enrolled seven patients who had previously received T-DM1 and a median of five lines of prior anticancer therapies. The patients had a median age of 59 and the confirmed objective response rate (ORR) was 57.1%, with a disease control rate of 100% for those treated with ARX788. All adverse events were well-tolerated and there were no serious adverse events or treatment discontinuations due to adverse events.

The study demonstrated a 51.7% overall response rate and 100% disease control rate after treatment with ARX788 in HER2-positive metastatic breast cancer patients who are resistant or refractory to T-DM1. The study was conducted in the US, Korea, and Australia. Four of seven patients were previously treated with HER2 tyrosine kinase inhibitors. No drug-related serious adverse events were reported.

“This preliminary safety and efficacy data in a heavily pretreated population further reinforces our view of the stability and precision underlying Ambrx’s proprietary drug-linker and site-specific conjugation technology for ADC design,” said Daniel O’Connor, Chief Executive Officer of Ambrx. “Our unique approach offers highly differentiated biologic design so that we can work towards providing better outcomes for patients with difficult-to-treat cancers.”

Ambrx's partner, NovoCodex Biopharmaceuticals, is conducting two Phase 3 studies and one Phase 2 study with ARX788 in China, with results expected in 2023.

Sara Hurvitz, M.D., Professor at David Geffen School of Medicine at UCLA, stated, “We are encouraged by the response rates and safety results, particularly given the significant need for new therapies among patients whose disease continues to progress after receiving multiple lines of therapy. We thank the San Antonio Breast Cancer Symposium for accepting our abstract as a Spotlight Poster Discussion presentation and the opportunity to show early results from the ACE-Breast-03 Phase 2 clinical trial.”

Shares of Ambrx Biopharma trade on the NYSE under the symbol AMAM. For more information visit www.ambrx.com.