Stereotactic Body Radiation Therapy and FES PET/CT Imaging for the Treatment of Oligoprogressive Estrogen Receptor Positive Metastatic Breast Cancer

Inclusion Criteria

• •Documented informed consent of the participant and/or legally authorized representative
• •Age: ≥ 18 years
• •Female or male
• •Eastern Cooperative Oncology Group (ECOG) ≤ 2
• •Ability to read and understand English or Spanish for questionnaires
• •Histologically confirmed ER+ (any progesterone receptor \[PR\] and human epidermal growth factor receptor 2 \[HER2\] status is allowed) metastatic breast cancer
• •The presence of metastatic breast cancer at the time of study entry with progression in 1-4 lesions (including new lesions). Patients that have disease progression in the breast and/or ipsilateral axilla will be considered to have only 1 site of progression even if multiple nodules/lymph nodes are present. Patients with progression in \> 4 lesions are not allowed. Patients with current progression of malignant pleural effusions, malignant ascites, abdominal carcinomatosis, and/or lymphangitic pulmonary involvement are considered to have \> 4 metastases (Note that patients with a history of these conditions earlier in the disease course with no evidence of progression of these conditions are eligible.)
• •Evidence of extracranial disease progression in 1-4 discrete lesions will be defined by either of the following:
• •* Progression of disease by Response Evaluation Criteria in Solid Tumors (RECIST) version (v) 1.1 or PET Response Criteria in Solid Tumors (PERCIST) v 1.0 criteria OR
• •* Progression of disease in at least 1 but up to 4 lesions as determined by the patient's treating oncologists such that the treating oncologist recommends changing to the next line systemic therapy. Note that a patient may not technically meet RECIST v 1.1 criteria for disease progression in this setting
• •SBRT must be feasible for all progressing lesions. Feasibility includes but is not limited to:
• •* All progressing lesions must have distinct borders AND
• •* Progressing lesions may not be located within 3 cm of previously irradiated critical structures such as the spinal cord, brachial plexus, brainstem, stomach, and/or small/large bowel that would render the metastasis unsafe to target with SBRT per the treating radiation oncologist
• •Patients with prior treated brain metastases that are stable are allowed. Patients must not have intracranial disease progression. Patients with prior or current leptomeningeal disease are not allowed
• •All progressing lesions must be amenable to stereotactic body radiation therapy to a dose of 30 Gy to 40 Gy in 3 to 5 fractions per the treating radiation oncologist
• •Women of childbearing potential (WOCBP): Negative urine or serum pregnancy test, If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required
• •Agreement by females and males of childbearing potential to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 1 months after the last dose of protocol therapy.
• •* Childbearing potential defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only)