The majority of deaths due to breast cancer occur in women with estrogen receptor alpha positive (ER+) disease. Endocrine therapy targets the estrogen signaling pathway controlling tumor growth and is standard treatment for women with ER+ primary and metastatic breast cancer. However, endocrine therapy is effective in some but not all women with ER+ tumors.
PET/MRI has the potential to provide a reliable test to measure functional endocrine sensitivity in a single patient, allowing for the development of more tailored treatment plans designed to most effectively treat a given patient and their disease. The progesterone receptor (PR) is regulated by estrogen. In this study, a PET tracer called FFNP that binds to the progesterone receptor is used to visualize the level of PR present, which is also indicative of endocrine sensitivity. When combined with the anatomical data provided by MRI, the overall expression of PR across the tumor can be visualized. The goal of this study is to test the accuracy of PET/MR imaging with FFNP in measuring PR expression in patients with invasive breast cancer.