This is a single institution, non-randomized, phase 1 with a dose expansion clinical trial investigating the addition of a novel agent, Avasopasem (GC4419), in patients with hormonal receptor positive (HR+) metastatic breast cancer with progression while on treatment with a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor and an aromatase inhibitor.

The first goal of this project is to validate the superiority of semi-permanent marks used in conjunction with specialized light-based surface imaging (SIGRT) in an effort to phase out the use of permanent tattoos for the investigator's patients. The secondary goal of this project is to validate the superiority of specialized light-based surface imaging for daily radiation set-up compared to standard-of-care imaging methods using ionizing radiation, such as weekly port films or cone-beam CT (CBCT) scans during a radiation therapy course for breast cancer.