This is single-arm open-label phase 1/2 trial assessing the safety and efficacy of the new drug, VS-6766, plus abemaciclib and fulvestrant in treating metastatic hormone receptor-positive and HER2-negative (HR+/HER2-) breast cancer.~VS-6766 is a unique small molecule drug that targets and interrupts a pathway that allows cancer cells to grow.The U.S. Food and Drug Administration (FDA) has not approved VS-6766 as a treatment for any disease. The FDA has approved abemaciclib and fulvestrant as a treatment option for breast cancer.~The study is divided into three study periods: a screening period; a treatment period; and a post-treatment follow-up period. Participants will receive study treatment for as long there are no serious side effects and the disease does not get worse.~It is expected that about 63 people will take part in this research study.~Verastem Oncology, a biopharmaceutical company, is supporting this research study by providing VS-6766 and funding to conduct this trial. Eli Lilly, a pharmaceutical company, is supporting this research study by providing the drug, abemaciclib.
This research is being done to evaluate the safety and effectiveness of a drug currently known as VS-6766 in combination with the drugs abemaciclib and fulvestrant in HR+/HER2-negative breast cancer.~The names of the study drugs involved in this study are:~VS-6766~Abemaciclib~Fulvestrant