The primary objective of this study is to assess the extent to which the Prosigna™ Breast Cancer Prognostic Gene Signature Assay affects the medical oncologist's treatment recommendations regarding adjuvant chemotherapy and actual treatments received for patients with early-stage breast cancer.

Changes in treatment recommendations will include (1) hormonal therapy alone, (2) hormonal therapy plus chemotherapy, and (3) changes in types of chemotherapy if chemotherapy was recommended before and after the test.

Inclusion Criteria:

• Resected node-negative, estrogen-receptor-positive, HER2-negative early- stage invasive breast cancer (T1-T2, N0, pN0 (i+), pN0 (mol+), M0)

  • Estrogen receptor status will be evaluated by Immunohistochemistry (IHC) and more than 1% of stained tumor cells will be considered positive.
  • HER2 status will be evaluated by IHC (0 or 1+, or 2+ will be considered negative) and by in-situ fluorescence hybridization.

• Postmenopausal women defined as:

  • Natural Amenorrhea > 12 months, regardless of age
  • Bilateral oophorectomy, regardless of age (the oophorectomy must have been carried out at least 4 weeks before entering the study)
  • Radiological castration with amenorrhea > 3 months, regardless of age
  • Hysterectomy and postmenopausal blood levels

• Able to give consent

• Eligible for treatment of breast cancer with adjuvant chemotherapy

• ECOG performance status of 0 or 1

Exclusion Criteria:

• Tumor size T3-T4

• Non-invasive breast cancer (e.g., Paget's disease, DCIS)

• Tumors with nodes that are not N0, pN0 (i+), or pN0 (mol+)

• Tumors that are estrogen-receptor negative or HER2 positive

• Have metastatic disease

• Unable to give informed consent

• Unable to complete patient reported outcome surveys

• Have contraindications for adjuvant chemotherapy

  • Age, performance status, significant comorbidities

• ECOG performance status > 1

Postmenopausal women with node-negative, estrogen-receptor positive, HER2-negative early-stage breast cancer. Investigators will offer enrollment to consecutively seen women who meet the entry criteria.