Prospective Observational Study Evaluating Treatment Decision Impact of Prosigna® in Early Stage Breast Cancer Patients

Inclusion Criteria:

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

  1. Estrogen receptor status will be evaluated by Immunohistochemistry (IHC) and more than 1% of stained tumor cells will be considered positive.
  2. HER2 status will be evaluated by IHC and/or by in-situ fluorescence hybridization (0 or 1+, or 2+ will be considered negative in the absence of in-situ fluorescence hybridization).
* Postmenopausal females, which is defined as:

  1. Natural Amenorrhea \> 12 months, regardless of age
  2. Bilateral oophorectomy, regardless of age (the oophorectomy must have been carried out at least 4 weeks before entering the study)
  3. Radiological castration with amenorrhea \> 3 months, regardless of age
  4. Hysterectomy and postmenopausal blood levels of FSH/LH
* Able to give informed consent
* Eligible for treatment of breast cancer with adjuvant chemotherapy, as determined by the treating physician
* ECOG performance status of 0 or 1

Exclusion Criteria:

* Tumor specimen from core needle biopsy (CNB)
* Tumor stage 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 (ER) negative or HER2-positive
* Have metastatic disease
* Have received another genomic test for prognosis of early breast cancer (i.e., Oncotype Dx, Mammaprint, or BCI)
* Unable to give informed consent
* Unable to complete patient reported outcome surveys
* Have contraindications for adjuvant chemotherapy, as determined by the treating physician

  o Age, performance status, significant comorbidities, etc.
* ECOG performance status \> 1