Oncotype DX® is likely to become more widely used in Europe as well as in Switzerland. The test is currently not reimbursed by the Swiss health insurances.

The proposed study will investigate to what extent adjuvant treatment recommendations in breast cancer patients with an ER-positive tumor, made by Swiss tumor boards, are based on conventional factors, and whether the recommendations would change, when RS results from the Oncotype DX® test were available.

In addition this study approaches the dilemma of adding adjuvant CT to adjuvant endocrine therapy in a systematic fashion. In this study, the St. Gallen consensus 2009 (with a minor update from the 2011 consensus, is used to predefine the patients suitable for endocrine therapy or chemo-endocrine therapy. Once results of this study are available they may help to better integrate Oncotype DX® with other factors. Currently, it is unclear how the different factors should be integrated into one recommendation.

This study will provide data on the usefulness of this test for the two patient groups which are suitable for hormone therapy only and for those who are considered for hormone plus chemotherapy.

Inclusion Criteria:

- Patients screening criteria

1. ≥ 18 years old female patients.
2. Resected primary breast cancer (R0 resection).
3. ER-positive breast cancer (defined as at least 10% ER-positive malignant cells).
4. HER2 negativity by IHC (0 or 1+) or by FISH (negative if ratio is ≤ 2.0).
5. pN0 or pN1a (1-3 positive nodes) by sentinel procedure or axillary dissection.

All patients matching the screening criteria should be recorded consecutively in the patient screening and enrollment list.

Patients inclusion criteria for baseline data collection

1. Signed informed consent form for participation to the baseline data collection.

   In addition, the following information must be available from the pathology report:

2. Estimation of the pathologic maximum tumor diameter (in mm).

3. Results of ER positive tumor cells (in %) and of PgR positive tumor cells (in %) of the invasive component.

4. Proliferation rate by Ki-67 staining (MIB-1 antibody) in %.

5. Result of modified Bloom-Richardson-Elston (BRE) Grading (Grade 1, 2 or 3).

Patients eligibility criteria for participation to the study Inclusion criteria

1. Signed informed consent form for participation to the study SAKK 26/10.
2. The patient is considered suitable to receive adjuvant chemotherapy (ie no medical contraindications to chemotherapy).
3. Invasive breast cancer tissue is available to prepare 39 sections (35 unstained + 4 H&E stained slides, thickness of 5 µm).
4. Performance Status: 0 or 1.

Exclusion criteria

1. Pregnancy
2. Bilateral invasive breast cancer
3. cT4 and pT4 tumors.
4. Patient with a current psychiatric or medical diagnosis that would interfere with her ability to participate in this study.
5. Known metastatic breast cancer (M1).

Patients with ER-positive, HER2 negative, pN0 or pN1a and resected primary breast cancer R0 resection.