Breast cancer (BC) is the most common cancer diagnosis among women and the incidence is increasing. Prognosis and treatment are dependent on the expression of estrogen receptors (ER) in the tumor. ER status is determined by immunohistochemistry (IHC) on biopsy tissue. The ER expression can change over time and be heterogeneous.

The IHC score on ER expression is subjective and can lead to intra and inter observer variability. A new computer image analysis software that can give the exact percentage of colored tumor cells on sectional tumor cuts has been developed.

It is also possible to quantify the ER expression non invasive by using the tracer 16α-18F-flour-17β-estradiol (FES) and in vivo positron emission tomography (PET) scans. FES-PET/CT has a high background activity in the liver which complicates the visualization of liver metastases. Theoretically, a new whole body parametric scan method makes it possible to distinguish background activity from uptake in liver metastases.

Malignant tumors often have an increased perfusion, and previous studies have found that tumors with low metabolism relative to blood flow have the longest disease free survival (DFS). To the best of our knowledge, no previous studies have examined the correlation between ER expression and blood flow.

Inclusion Criteria:

• Patients with known disseminated breast cancer
• Metastatic ER+ HER2- breast cancer with metastases in the liver, at least two separate liver foci visualised on CT
• Diagnostic CT scan done in connection with clinical control
• Treatment with aromatase inhibitors, and potential additional treatment
• Postmenopausal

Exclusion Criteria:

• Treatment with Tamoxifen or Fulvestrant completed within 5 weeks prior to FES-PET/CT
• ER- metastases
• Life expectancy under three months
• Claustrophobia
• Any pain which makes it impossible to lie in the scanner for 90 minutes