BTX-A51 + fulvestrant

BTX-A51 + fulvestrant is an investigational **combination therapy** of two drugs for advanced solid tumors, particularly estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer. **BTX-A51** is a first-in-class, orally administered, small molecule, multi-kinase inhibitor and PROTAC (proteolysis-targeting chimera) that co-targets and degrades cancer cell regulators such as casein kinase 1 alpha (CK1α), cyclin-dependent kinase 7 (CDK7), and cyclin-dependent kinase 9 (CDK9), resulting in activation of tumor suppressor p53 and downregulation of oncogenes including MYC and MCL-1. **Fulvestrant** is a selective estrogen receptor degrader (SERD) that binds, blocks, and accelerates the degradation of the estrogen receptor, leading to suppression of estrogen-mediated signaling in breast cancer cells. The combination is under Phase 1 clinical evaluation for safety and tolerability in patients with advanced solid tumors[1][2][3][4][6].