Prospective Pilot Study of ¹⁸F-Fluoroestradiol PET/CT in Patients With Invasive Lobular Carcinomas

Area of Science:

• Oncology
• Nuclear Medicine
• Radiology

Background:

• ¹⁸F-fluoroestradiol (FES) PET/CT, approved in 2020, visualizes estrogen receptor (ER)-expressing tissues.
• Invasive lobular carcinoma (ILC) frequently exhibits ER positivity, making it a target for FES PET/CT.

Purpose of the Study:

• To determine the frequency of abnormal uptake at histologically confirmed invasive lobular carcinoma (ILC) sites using ¹⁸F-fluoroestradiol (FES) PET/CT.
• To compare the diagnostic performance of FES PET/CT with FDG PET/CT for ILC detection.

Main Methods:

• A prospective, single-center pilot study enrolled patients with confirmed ILC from December 2020 to August 2021.
• FES PET/CT and optionally FDG PET/CT were performed. Two nuclear radiologists assessed abnormal uptake at known ILC sites and additional lesions.
• The primary endpoint was the percentage of known ILC sites with abnormal FES uptake, hypothesized to exceed 60%.

Main Results:

• The analysis included 17 patients with 25 confirmed ILC sites. FES PET/CT showed abnormal uptake in 88% (22/25) of lesions, significantly exceeding the 60% threshold (p=0.002).
• FES PET/CT identified 17% (4/23) of ILC sites exclusively, while FDG PET/CT identified only 4% (1/23).
• FES PET/CT revealed additional, previously undetected lesions in 24% (4/17) of patients, leading to clinical stage changes in 18% (3/17).

Conclusions:

• The study met its primary endpoint, demonstrating significantly high abnormal FES uptake in known ILC sites.
• FES PET/CT shows superior detection rates compared to FDG PET/CT for ILC.
• FES PET/CT holds promise as a valuable tool for evaluating patients with invasive lobular carcinoma.