This phase II trial evaluates the effect of capecitabine on tumor response using imaging and tumor markers to adjust dose (adaptive therapy) in patients with estrogen receptor (ER) positive, HER2 negative breast cancer that has spread from where it first started to other areas in the body (metastatic). Capecitabine is in a class of medications called antimetabolites. It is taken up by tumor cells and breaks down into fluorouracil, a substance that kills tumor cells. Adaptive therapy with capecitabine based on tumor burden response may slow or stop the growth of tumor cells in patients with metastatic ER positive, HER2 negative breast cancer.
PRE-REGISTRATION: Provide written informed consent Note: Pre-registration should occur prior to screening research blood draws being completed
PRE-REGISTRATION: Provider anticipates the patient will begin on capecitabine within 14 days or has started capecitabine within the past 42 days and has had a maximum of two cycles Note: Pre-registration should occur prior to screening research blood draws being completed
Age ≥ 18 years
Histological confirmation of estrogen-receptor positive (ER+), HER2-negative overexpression or amplification negative as per American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines, metastatic breast cancer
Prior chemotherapy or use of antibody drug conjugate in the metastatic setting
Note - Cohort 2 only: Patients can have had up to two cycles of capecitabine before joining the study
Pregnant persons
Nursing persons
Single group
Biospecimen Collection
Procedure/SurgeryUndergo blood sample collection
Bone Scan
Procedure/SurgeryUndergo bone scan
Capecitabine
DrugGiven PO
Computed Tomography
Procedure/SurgeryUndergo CT
Magnetic Resonance Imaging
Procedure/SurgeryUndergo MRI
Questionnaire Administration
Other interventionAncillary studies
Ability to achieve adaptive therapy (AT)
Will be assessed by the proportion of patients (%) who are able to receive 2 or more cycles of AT with capecitabine divided by the total number of patients who have entered the AT phase of treatment (have stable or responsive disease).
Time to progression
Time to progression will be defined as the time from registration to the earliest date of documentation of disease progression.
Overall survival (OS)
OS will be defined as the time from registration to death due to any cause.
Cumulative dose
The cumulative dose of capecitabine administered per patient will be assessed across patients receiving AT.
Incidence of adverse events (AEs)
The maximum grade for each type of AE will be recorded for each patient. Adverse events will be categorized according to Common Terminology Criteria for Adverse Events (CTCAE) v5.0.
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