Longitudinal ctDNA Surveillance for Older Women With ER+ Breast Cancer Who Omit Surgery

Inclusion Criteria: * early-stage (stages I-III) breast cancer * estrogen receptor positive (ER+) and/or progesterone receptor positive (PR+) and HER2 receptor negative * able to provide blood samples * decision made by treating physician and patient to forego upfront surgery in favor of medical management with endocrine therapy * non-metastatic disease at diagnosis (patients need not have staging scans; patients at higher risk for de novo stage IV disease should not have any symptoms concerning for metastatic disease) * patients may be taking any endocrine therapy * patients may be taking any CDK4/6 inhibitor as deemed necessary by their treating physician * any ECOG Performance Status allowed * if patients have synchronous bilateral ER+ breast cancer, tissue from both sites should be submitted to Natera to perform ctDNA testing * patients with multifocal/multicentric tumors are eligible and the largest focus of cancer should be submitted for testing Exclusion Criteria: * under 70 years of age * breast cancer that is not estrogen receptor positive (ER+) or progesterone receptor (PR+) * unable to provide blood samples or insufficient tumor tissue for Signatera testing