FLT PET in Measuring Treatment Response in Patients With Newly Diagnosed Estrogen Receptor-Positive, HER2-Negative Stage I-III Breast Cancer

Inclusion Criteria:

* A new diagnosis of invasive breast cancer \> 1.0 cm in size, ER+ clinical stage I-III
* Patient must have surgical resection followed by systemic adjuvant therapy with an aromatase inhibitor (AIs) as part of planned treatment; any approved AI at standard clinical dosing may be used; in pre-menopausal patients, ovarian suppression with a gonadotropin-releasing hormone (GnRH) agonist will be started prior to initiation of the AI on a separate clinical trial in parallel with the imaging study
* Have tissue block available from core biopsy for correlative biomarkers and genomic assay
* Have menopausal status determined prior to study enrollment; for study purposes, postmenopausal is defined as

  * A prior documented bilateral oophorectomy, or
  * A history of at least 12 months without spontaneous menstrual bleeding, or
  * Age 60 or older with a prior hysterectomy without oophorectomy, or
  * Age less than 60 with a prior hysterectomy without oophorectomy (or in whom the status of the ovaries is unknown) with a documented follicle-stimulating hormone (FSH) level demonstrating confirmatory elevation in the postmenopausal range for the lab
* Negative pregnancy test within 7 days of baseline positron emission tomography (PET) scan for pre-menopausal patients
* Tumor HER2/neu expression must be determined (as part of standard clinical care) prior to study enrollment; HER2 may be tested by any Food and Drug Administration (FDA) approved HER2 testing method; if determination is intermediate by immunohistochemistry (IHC), fluorescent in situ hybridization (FISH) or another alternate HER2 test must be performed
* Be a candidate for \[18F\]FLT PET imaging
* Be informed of the investigational nature of this study and provide written informed consent in accordance with institutional and federal guidelines prior to study-specific screening procedures
* Be willing and able to comply with scheduled visits and other trial procedures

Exclusion Criteria:

* Current use of aromatase inhibitor as prevention or treatment for breast cancer
* Life expectancy of less than two months
* HER2/neu positive by IHC and/or another FDA approved HER2 testing method
* Inability to tolerate scanning (e.g. - claustrophobia, severe pain)
* Weight exceeding capacity of imaging table