This clinical trial will investigate an estrogen-regulated parameter as an early measure of
endocrine therapy response: progesterone receptor (PR) protein with a progestin-based
radioligand, 18F-fluorofuranylnorprogesterone (18F-FFNP). The overall purpose of this
research is to test the efficacy of 18F-FFNP PET/MRI for predicting response to presurgical
endocrine therapy and to determine the quantitative reliability of 18F-FFNP breast PET/MRI in
patients with newly diagnosed ER+/PR+/HER2- primary breast cancer.