Endocrine therapies have been associated with an overall survival benefit in breast cancer and are the preferred initial treatment approach in patients with ER+, HER2- metastatic breast cancer. Unfortunately, resistance to endocrine therapies eventually develops in the metastatic setting and metastatic breast cancer remains an incurable disease. Endocrine resistance may develop as a result of alterations in estrogen signaling and metabolism pathways, which may be modulated by gut bacteria. In addition, genomic profiling of archival tissues and circulating tumor DNA (ctDNA) in ER+ breast cancer has identified multiple somatic molecular alterations that may mediate response to endocrine therapies.
This study is designed to identify markers of endocrine resistance in ctDNA and the gut microbiome in patients with ER+ HER2- metastatic breast cancer.
