A prospective population-based cohort study is being conducted in Ontario to evaluate whether the performance of Oncotype DX® changes the treatment recommended and the treatment received in women or men with node negative, ER positive breast cancer who are receiving (or will receive) endocrine therapy and who are candidates for chemotherapy. One thousand eligible consenting women and men will have their tumor tissue specimen sent to Genomic Health where the Oncotype DX® assay will be performed.

The evidence supporting the adoption of Oncotype DX® is relatively weak by the criteria used by the Ontario Health Technology Advisory Committee (OHTAC). There is only one small published prospective study that reports on Oncotype DX® changing clinical management. The economic models that estimated the potential advantages of using an Oncotype DX® guided treatment strategy may have overestimated the benefits because they assumed that all patients with tumors >1cm in the absence of Oncotype DX® testing would receive chemotherapy in addition to tamoxifen, and that the magnitude of benefit with chemotherapy over tamoxifen is relatively large, i.e. reduces recurrence risk by 74% and associated with an absolute benefit of 28%. (The benefit comes from one trial and is applied to all patients). It is estimated that there are about 3,300 incident cases with node negative, ER positive, HER2 neu negative tumors annually in Ontario, it is important to evaluate the adoption of this test for decision making in Ontario.

Inclusion Criteria:

• Women or men with histologic evidence of invasive breast cancer (ductal, lobular or mixed disease).

• Surgical resection including breast conserving surgery or modified radical mastectomy or simple mastectomy, within the last four months.

• Axillary lymph nodes assessed for tumor by:

  (i) sentinel node biopsy, or (ii) axillary node dissection, or (iii) both

• Axillary lymph node assessment negative for cancer, or positive only for micrometastases (i.e., cancer <2mm by H&E stain).

• Tumor is estrogen receptor (ER) positive.

• Receiving or to receive adjuvant endocrine therapy (i.e., tamoxifen or aromatase inhibitor).

• Being considered for adjuvant chemotherapy.

Exclusion Criteria:

• Axillary lymph node positive for cancer.
• Patients with inoperable locally advanced breast cancer.
• Metastatic breast cancer, including local ipsilateral recurrence.
• HER2 neu positive.
• Physician/Patient unwilling to comply with study protocol.
• Inability to provide informed consent (e.g. dementia or severe cognitive impairment).