Overview

The purpose of this study to compare two types of cancer imaging scans to see which is better at detecting and monitoring metastatic ILC. This study will compare PET/CT (positron emission tomography/computed tomography) scans using the radiotracer fluorine 18 (18F)-fluoroestradiol (FES) with a standard imaging approach for detecting and monitoring ILC, PET/CT scans using the radiotracer 18F-fluorodeoxyglucose (FDG). These scans will be referred to as FES PET/CT scans and FDG PET/CT scans.

Eligibility

Inclusion Criteria:

• Adult patient > 18 years old
• Biopsy-proven metastatic ILC
• Confirmed ER+ breast cancer from either primary tumor or metastatic biopsy (ER receptor percent staining ≥ 10% of tumor cells by IHC)
• HER2-negative per ASCO/CAP
• ECOG Performance Status Score of 0, 1 or 2.
• Patient can have received up to 2 lines of therapy in the metastatic setting
• Life expectancy of at least 12 months

Exclusion Criteria:

• Low ER expression defined as ER <10% of tumor cells by IHC
• Patients who have been on adjuvant ER-blocking endocrine therapy with SERM or SERD without an 8- and 24-weeks washout, respectively. (The use of aromatase inhibitors or ovarian suppression is permitted given that they do not block estrogen receptors).
• Pregnancy or lactation or parturient or nursing mother
• Patient presents with any other clinically active, serious, life-threatening disease, medical, or psychiatric condition, and/or who has a life expectancy of <12 months, or for whom study participation may compromise their management; and/or a patient who the investigator judges to be unsuitable for participation in the study for any reason.