in preparation for an amendment

To investigate prospectively whether short term endocrine treatment can induce molecular changes, predictive for therapy response.

We will perform a randomized, open-label, single-institution study. It will compare the efficacy of three different endocrine treatment regimens (Anastrozole +/- Fulvestrant or Tamoxifen) in changing proliferation-index and inducing apoptosis during a 2-6 week pre-operative treatment period in breast cancer patients. These results will be correlated to gene expression profiles, phosphorylation status of the ER, SNPs in CYP450 sequences, tamoxifen metabolite concentrations, changes in estrogen serum levels and protein expression patterns.

Inclusion Criteria:

• Patients with proven invasive adenocarcinoma of the breast
• Any tumor with a size ≥ 1cm (NOT inflammatory breast cancer)
• WHO-performance score 0 or 1
• Written informed consent

Exclusion Criteria:

• Clues of metastatic disease by clinical examination according to most recent NABON guidelines
• Multicentric breast cancer
• Inflammatory breast cancer
• Hormone replacement during the last 12 months
• Other systemic treatment during the waiting time till surgery
• Already planned date for surgery within the next 2 weeks
• Any psychological, familial, sociological or geographical condition potentially hampering adequate informed consent or compliance with the study protocol
• Patient's refusal to undergo a core biopsy procedure of the primary tumor before the start of treatment

NB: a concomitant malignancy within the last five years is not an exclusion criterium, because survival is not the primary endpoint. Just as prior invasive breast cancer or DCIS within the last 15 years is not an exclusion criterium.

NB: Patients of childbearing potential must implement adequate non-hormonal contraceptive measures during the study.