A Study of a New Drug Combination, Copanlisib and Fulvestrant, in Advanced Breast Cancer

This phase I/II trial studies the side effects and how well copanlisib works when given together with fulvestrant in treating patients with estrogen receptor positive (ER+) and human epidermal growth factor receptor 2 negative (HER2-) breast cancer that has spread to other places in the body (advanced) and progressing after prior treatment. HER2 and ER are two types of proteins called receptors that can affect the growth of breast cancer cells. Additionally, investigators hope to learn from this study if tumor genetic information is important for predicting whether this type of breast cancer will respond to fulvestrant and copanlisib. Copanlisib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Hormone therapy using fulvestrant may fight breast cancer by blocking the use of estrogen by the tumor cells. Giving copanlisib and fulvestrant may work better in treating patients with ER+ and HER2- breast cancer compared to fulvestrant alone.