S1703 Serum Tumor Marker Directed Disease Monitoring in Patients With Hormone Receptor Positive Her2 Negative Metastatic Breast Cancer

Inclusion Criteria: * STEP 1 REGISTRATION * Patients must have a diagnosis of hormone receptor positive (estrogen receptor positive \[ER+\] and/or progesterone receptor positive \[PR+\]), HER-2 negative, metastatic (M1) breast cancer and must be receiving or plan to receive first-line systemic treatment for metastatic disease. (Systemic treatment is any treatment meant to treat the whole body such as endocrine therapy +/- targeted therapy +/- chemotherapy). * NOTE: Participants are eligible if they have either de-novo metastatic breast cancer and/or recurrent breast cancer from an earlier stage that is now metastatic * Patients must be registered to step 1 between 14 days prior to and 60 days after start of first-line systemic treatment for metastatic disease * Patients must have been tested for the following breast cancer specific STMs after diagnosis of metastatic disease and within +/-14 days of initiation of first-line systemic treatment for metastatic disease: * CEA (must be tested) * CA 15-3 or CA 27.29 (at least one of these must be tested) * At least one of the tested STMs must have been \>= 1.5 x the institutional upper limit of normal at this time. Testing all three STMs is encouraged but only two are required. Patients must plan to have the same two STMs tested for the duration that the patient is on protocol-specified disease monitoring. * Patients must have systemic radiographic imaging prior to initiation of systemic therapy or within 30 days of ini…