Using FDG-PET/CT to Assess Response of Bone-Dominant Metastatic Breast Cancer, FEATURE Study

Inclusion Criteria:

• Patients must have an Eastern Cooperative Oncology Group (ECOG) performance (performance status [PS]) =< 2

• Patients with histologically confirmed metastatic breast cancer by local assessmentthat is hormone receptor positive by American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines and with known HER2 status

• Patients must have radiologically confirmed bone-dominant (BD) or bone-only (BO)disease

• BD defined as disease involving bone with or without limited measurablemetastases by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, with >= 1 non-irradiated bone metastasis on bone scintigraphy

• NOTE: Limited measurable metastases includes lymph nodes and the softtissue components of lytic or mixed lytic/blastic bone metastases. Anynumber of lymph nodes < 3 cm and up to 2 lymph nodes > 3 cm will beallowed. Up to 5 measurable soft tissue components of lytic or mixedmytic/blastic bone metastases will be allowed

• BO defined as detectable disease confined within the bone (any site, any numberof lesions). Diagnosis requires abnormalities identified by imaging (bone scan,CT +/- PET +/- magnetic resonance imaging [MRI]) with no other sites ofmetastases identified and with >= 1 non-irradiated bone metastasis on bonescintigraphy

• Patients must have no contraindication to FDG-PET imaging

• Patients must have one of the following systemic therapies:

• Plan to receive either 1st or 2nd line endocrine therapy for metastatic breastcancer. Endocrine therapy may include selective estrogen receptor modulators (SERMs), aromatase inhibitors, and/or fulvestrant that may be combined withFood and Drug Administration (FDA)-approved biologic agents (palbociclib,ribociclib, abemaciclib, everolimus, alpelisib)

• Chemotherapy per National Comprehensive Cancer Network (NCCN) or institutionalstandard. Use of colony stimulating growth factor must be suspended for >= 14days prior to FDG-PET/CT scans at baseline and 12-weeks

• Plan to receive HER2-targeted therapy per ASCO, NCCN, and/or institutionalguidelines as indicated for patients with HER2 positive disease. WhenHER2-targeted therapy is used with chemotherapy, use of colony stimulatinggrowth factors is NOT expected or should be suspended for a minimum of 2 weeks,but preferably for at least 3 weeks prior to the required FDG-PET/CT scan timepoints

• The use of bone-stabilizing agents (bisphosphonates or denosumab) is permitted

• Patient must meet institutional guidelines for renal function for MRI and CTscanning

• Patient's life expectancy must be estimated at >= 24 weeks

• The patient is participating in the trial at an institution which has agreed toperform the imaging research studies, completed the ECOG-American College ofRadiology Imaging Network (ACRIN) defined PET/CT scanner qualification proceduresand received ECOG-ACRIN PET/CT scanner approval

• Patients must complete the baseline (T0) FDG-PET within 28 days prior toregistration or within 28 days after registration

• For patients completing the baseline (T0) FDG-PET AFTER registration allparameters must be met

• For patients who completed the baseline (T0) FDG-PET prior to registration thefollowing tests are exempt:

• Pregnancy testing documentation prior to FDG-PET (T0 time point)

Exclusion Criteria:

• Patients with RECIST 1.1 measurable lesions in viscera, active central nervoussystem (CNS), leptomeningeal carcinomatous or pleural or peritoneal disease will notbe eligible. Patients with prior CNS metastases treated with radiation or resectionand without evidence of clinical or radiographic progression within 28 days ofregistration are eligible

• Patients who have received greater than 3 lines of cytotoxic chemotherapy formetastatic breast cancer are not eligible

• Patients currently participating in or have participated in a study of aninvestigational agent or using an investigational device within 3 weeks of studyregistration are not eligible

• Patients with known additional malignancy that is progressing or requires activetreatment are not eligible. Exceptions include basal cell carcinoma of the skin,squamous cell carcinoma of the skin, or in situ cervical cancer that has undergonepotentially curative therapy

• Women must not be pregnant because FDG is a radiopharmaceutical with the potentialfor teratogenic effects and PET/CT involves additional radiation exposure. Inaddition, because of radiation exposure to a nursing infant from FDG, women who arebreastfeeding are also excluded from this study. All females of childbearingpotential must have a blood test or urine study within 7 days prior to FDG-PET/CT torule out pregnancy. Patients are excluded from this if baseline FDG-PET/CT scan metstudy parameters and was completed within 28 days of study registration