Brief summary

Breast cancer is not only the leading cause of cancer in women, but also the leading cause of cancer deaths in women. Estrogen receptor-positive and HER2-negative breast cancer is the most prevalent breast cancer subtype. Endocrine therapy is the mainstay of treatment; however, due to the varied nature of the disease, development of resistance to this therapeutic approach is very common in the metastatic setting. The purpose of this study is to see whether the effectiveness of elacestrant can be enhanced by combining it with a targeted agent such as a CDK4/6 inhibitor to treat patients with ER+/HER2- or metastatic breast cancer with prior exposure to a CDK4/6 inhibitor.