Phase 1b study of zilovertamab plus paclitaxel for locally advanced/unresectable or metastatic HER2-negative breast cancer

Zilovertamab is a humanized monoclonal antibody targeting ROR1, an onco-embryonic antigen expressed by malignant cells of a variety of solid tumors, including breast cancer. A phase 1b study at University of California San Diego (La Jolla) evaluated the combination of zilovertamab and paclitaxel in patients with locally advanced/unresectable or metastatic HER2-negative breast cancer. Study patients had received a median of 4 prior therapies. No patients discontinued therapy due to toxicity ascribed to zilovertamab. Adverse events were consistent with the known safety profile of paclitaxel. Among 16 patients, Partial response and stable disease as best tumor response were seen in 6 (38%) and 6 (38%), respectively. The authors conclude that the combination of zilovertamab and paclitaxel was safe and well tolerated in heavily pretreated advanced breast cancer patients. Further evaluation of ROR1 targeting with zilovertamab in breast cancer patients is warranted.