HER2/neu (often shortened to HER2) is a growth-promoting protein on the outside of all breast cells. Breast cancer cells with higher than normal levels of HER2 are called HER2-positive. These cancers tend to grow and spread faster than other breast cancers. Breast cancer is the most commonly diagnosed cancer in women, with over 40,000 women in the United States expected to die from advanced metastatic disease in 2018. Approximately 20% to 25% of breast cancers overexpress HER2, which is an established therapeutic target of both monoclonal antibodies (mAbs) and receptor tyrosine kinase inhibitors. With the advent of effective mAbs directed against HER2, the median overall survival of patients with metastatic HER2+ breast cancer has improved. However, management of metastatic disease in the central nervous system (CNS), observed in up to 50% of HER2+ breast cancer patients, continues to be a clinical challenge in large part due to the inability of mAbs to sufficiently cross the blood–brain barrier. Although small-molecule inhibitors of HER2 exist and have been clinically approved, their single-agent efficacy in the context of metastatic disease to the brain has been limited. While HER2-targeted therapy in combination with conventional agents has shown some promise for the treatment of patients with metastatic breast cancer, control of brain metastases remains a significant unmet clinical need, as most patients survive less than two years following CNS involvement. Recent advances in cellular immunotherapy approaches have underscored the potential for potent antitumor immune responses and clinical benefit against solid cancers, and these approaches may be effective in the treatment of HER2+ breast cancer that has metastasized to the brain. Likewise, HER2 has been suggested as a suitable target for glioblastoma (GBM), wherein elevated HER2 protein levels have been correlated with impaired survival.

CAR-based T-cell immunotherapy is being actively investigated for the treatment of solid tumors, including HER2+ cancers. Our academic partners at COH have developed a second-generation HER2-specific CAR T-cell therapy for the treatment of breast cancer that has metastasized to the brain. COH’s preclinical data demonstrate effective targeting of breast cancer brain metastases with intraventricular delivery of HER2-BBζ CAR T cells. COH is evaluating the safety of this HER2-specific CAR T cell therapy in a phase I/II glioblastoma trial that began recruiting patients in Q2 2018. A second trial for the treatment of breast cancer metastatic to brain will open in Q4 2018.