Determinants of Resistance to Endocrine Therapy and a Cyclin-dependent Kinases 4 and 6 (CDK4/6) Inhibitor for HR+ MBC

The goal of this research study is to determine if the investigators can predict which participants will respond to endocrine therapy and a cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor for metastatic breast cancer and which participants will not. Investigators will use information from the tumor tissue and serial blood samples. Investigators hope that a deeper understanding of which participants will respond to this combination and how resistance emerges will allow the investigators to better tailor therapies for metastatic breast cancer. Subjects will have archived tissue or new biopsy collected at study enrollment. This tissue will undergo special molecular testing. Subjects will also have blood collected at study enrollment and periodically thereafter. This blood will also undergo special molecular testing. Information from this testing will not be available to subjects or their treating physicians as the investigators do not know how this information should impact treatment. The investigators will collect information about which treatment the subjects receive and how their cancer responds. Any man or woman being seen at Johns Hopkins for treatment of newly diagnosed estrogen receptor positive (ER+) and/or progesterone receptor positive (PR+) metastatic breast cancer may be eligible.

NCT Number	NCT03439735
Lead Sponsor	Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins Collaborators: Safeway Foundation, Biovica International AB
Conditions	Breast Cancer
Enrollment	45 participants
Start Date	2018-07-20
Primary Completion	2027-08-01 (estimated)
Study Completion	2027-11-01 (estimated)
Updated on ClinicalTrials.gov	2026-08-07