Molecular Breast Imaging (MBI) is a highly promising novel methodology for breast cancer detection. Preliminary patient studies with our dual-detector system indicate that this system is capable of reliably detecting very small (5-10 mm) malignant lesions in the breast. Besides the usefulness of MBI for tumor detection we speculate that tumor uptake and washout may be predictors to response to neoadjuvant therapy for patients with the diagnosis of breast cancer. We propose to evaluate this system in patients undergoing neoadjuvant therapy for breast cancer with the aims to determine 1) if pre- and post-neoadjuvant therapy tumor size can be satisfactorily assessed by MBI and corresponds to tumor size evaluation by conventional imaging procedures 2) if post-neoadjuvant tumor size as determined by MBI corresponds to size found at surgery 3) if tumor uptake and washout are predictors of response to neoadjuvant therapy.

We plan to recruit 20 patients who present to the Internal Medicine Breast Cancer Clinic with breast cancer and who after discussion with the consulting surgeon and oncologist have agreed to undergo neoadjuvant chemotherapy or neoadjuvant hormone therapy. After having undergone routine imaging studies as determined by the breast clinic physician, participation in the MBI neoadjuvant study will be offered to these patients. The study coordinator will approach and inform them of the research project. If they are interested in participating, informed consent will be obtained and the patient will be scheduled for the MBI study. The patient's neoadjuvant therapy will be arranged by the consulting oncologist. The MBI study will be scheduled to not delay administration of neoadjuvant therapy and will be done prior to or within 24 hours of adjuvant therapy administration. Various regimens are being used for neoadjuvant chemotherapy, most treatment guidelines including an initial anthracycline-containing regimen. Taxanes add substantial efficacy to some patients and are increasingly being used for patients with node-positive breast cancer. Neoadjuvant hormone therapy is used for selected patients with estrogen receptor (ER)-positive breast cancer. The consulting oncologist will decide which regimen to use in a particular patient, including the possibile enrollment in a trial evaluating different neoadjuvant agents.

The optimal duration of induction chemotherapy has not been established in randomized controlled trials. Limited information from clinical reports suggests that the pace of response to neoadjuvant chemotherapy is variable. Some patients achieve maximal tumor reduction after only one or two cycles, while others require more therapy. Response to neoadjuvant hormone therapy is often assessed at the end of three to four months.

Following neoadjuvant therapy a careful physical examination with measurements to document the extent of residual disease in breast and regional lymph nodes accompanied by repeat imaging studies like mammogram, ultrasound, and MRI are done. At this time, the patient will undergo a follow-up MBI study. Measurements documented in the patients records will be used for analysis.

After completion of neoadjuvant therapy, the patient will usually undergo local therapy consisting of mastectomy or BCT. The pathology report will provide us with the definite size of the remaining tumor.

Inclusion Criteria

• Women with breast cancer scheduled to undergo neoadjuvant chemotherapy therapy or neoadjuvant hormone therapy and who have undergone any breast imaging procedure, and in whom a repeat imaging procedure is planned prior to definite surgery. MRI of the breast for accurate tumor size evaluation is recommended but not necessarily required for study inclusion.