This research study is evaluating a genomic analysis called Predictor Analysis of Microarray 50 (PAM50, by Prosigna®) as a tool to possibly guide the participant and the treating physician to choose the most personalized pre-operative treatment for breast cancer.

As the investigators understanding of how ER-positive breast cancer (a type of cancer in which the cells need the hormone estrogen to grow) improves, more treatment decisions are being tailored to an individual's unique genetic makeup. National medical guidelines now include the routine use of tumor profiling tests, like the Prosigna® assay, which look at the gene activity of a person's cancer cells to determine the likely outcome or course of a disease (prognosis) and predict the benefit of chemotherapy or endocrine therapy after breast surgery.

Currently, the Prosigna® assay (also called PAM-50) is FDA approved as a tool that physicians can use to help make decisions about a patient's treatment after their breast surgery. In these cases, physicians run this test using tumor tissue from a patient's breast surgery. However, the Prosigna® assay is not approved for use preoperatively, or before surgery.

Previous studies showed that the Prosigna® assay was able to identify tumor types that were more likely to benefit from treatment before surgery (whether it's hormonal therapy or chemotherapy). In this study, the investigators will use tumor tissue from the participant's biopsy to run the Prosigna® assay. The test may give both the participant and the investigators more information about the best possible treatment option for the participant before surgery.

This study is being done to determine how Prosigna® assay results may affect the physician's choice of treatment before surgery and how well patients understand the test and its implications.

Inclusion Criteria:

• Patients pre- or post-menopausal must have histologically confirmed early stage/locally advanced invasive breast cancer
• ER or PR ≥ 1% by immunohistochemistry (IHC)
• HER2-negative status, according to guidelines by ASCO CAP guidelines:

https://www.asco.org/practice-guidelines/quality-guidelines/guidelines/breast-cancer#/9751

• Tumor size ≥ 0.5cm (clinical or radiographic measurements)
• Any nodal status allowed
• Age > 18 years old
• Felt to be a possible candidate for neoadjuvant systemic therapy by their treating physician

Exclusion Criteria:

• ER-negative and PR-negative invasive breast cancer (< 1% by IHC)
• Known metastatic disease

Patients that are considered possible candidates for neoadjuvant treatment, irrespective whether chemotherapy or endocrine therapy, by clinical-pathologic features.