To Identify Small Bowel Metastasis From Lobular Breast Cancer on ¹⁸F-Fluoroestradiol PET/CT: Necessary to Adjust the Background Uptake Level

A 61-year-old woman was incidentally found to have small bowel metastasis from an undiagnosed lobular breast cancer in a workup for her acute presentation of small bowel obstruction. However, outside-hospital mammogram and breast ultrasound failed to reveal primary breast cancer. At 3.5 months postsurgery, the patient transferred her care to our hospital and received initial staging 18F-fluoroestradiol (FES) PET/CT. The occult primary right breast cancer and previously biopsied right axilla lymph node were visualized on FES PET/CT. The intense small bowel uptake of FES was initially considered as physiological; however, after readjusting the background FES level on PET, an intense focus at small bowel anastomosis site became obvious.