Title
A Diagnostic Accuracy Study of FES PET/MRI for the Detection of Occult Disease in Lobular Breast Cancer

Description
The investigators hope to learn if lobular breast cancer can be identified using a special procedure called a positron emission tomography (PET) magnetic resonance image (MRI) scan, collectively a PET/MRI scan, that uses a radioactive imaging agent called Fluorine 18 fluoroestradiol (18F-FES). This procedure may be able to define the extent of disease more clearly than the standard of care breast imaging exams. 30 participants will be enrolled and be on study for up to 6 months.

Objective
Primary Objective: To estimate the increased sensitivity of 18F-FES PET/MRI for detecting disease that is occult on SOC imaging

Secondary Objectives: To characterize the
- Positive predictive value of additional pathology-confirm disease.
- Proportion of upstaging (composite T, N and M stages)
- Frequency of extensive breast disease (e.g., multifocal, multicentric or contralateral).
- Change in clinical management (e.g., changes in treatment intent, conversion to neoadjuvant therapy).
- Agreement of ILC tumor size between imaging exams (18F FES PET-MRI and SOC breast MRI, ultrasound and mammogram) and histopathologic exams.
- Error rate in size measurements between radiology and pathology for primary ILC.
- Change in surgical management (e.g., conversion to mastectomy).

Exploratory objectives: 1) To correlate 18F-FES standardized uptake value of SUVmax with immunohistochemical quantification of ER expression and ILC cellularity. 2) To define an 18F-FES SUVmax threshold for pathology-confirmed ER-positive ILC.

Treatment This prospective study aims to estimate the added value of supplemental 18F-FES PET/MRI following standard-of-care (SOC) preoperative assessments for detecting occult disease in ILC. The investigators hypothesize that there is increased sensitivity of 18F-FES PET/MRI for detecting additional locoregional and distant site(s) of disease that is occult on SOC imaging.

Key Eligibility Inclusion Criteria:

- Adults assigned female sex at birth
- Newly diagnosed ILC confirmed on core-needle biopsy (greater than or equal to 1 percent ER staining per American Society of Clinical - - Oncology/College of American Pathologists (ASCO/CAP) guidelines)
- have undergone or will undergo standard-of-care (SOC) clinical and imaging assessments (e.g., mammography, ultrasound, breast MRI)
planning for mastectomy or breast-conserving surgery within 12 months of their initial diagnosis
- Provision of signed and dated informed consent form

Applicable Disease Sites
Breast

Participating Institutions
UW Health Eastpark Medical Center; UW Health University Hospital; Wisconsin Institute for Medical Research (WIMR)