Aim: This study examines the combination of FES-PET and FDG-PET as complementary imaging for detection of metastatic ILC.
Methods: We retrospectively evaluated FES and FDG uptake in patients with metastatic ILC from an estrogen receptor (ER) positive primary tumor. We classified lesions into three categories (FES high/FDG low, FES high/FDG high, FES low/FDG low) using SUVmax cut-off values of 1.5 for FES and 5.0 for FDG. Qualitative evaluation included examination of the difference in the extent of disease between FES and FDG.
Results: Of the 38 patients, 82% had FES uptake in all tumor sites identified by FDG, with 18% lacking FES uptake in at least one lesion. Mean (range) SUVmax for FES and FDG was 4.0 (0.67-10.6) and 4.6 (1.3-12.5), respectively. The majority of ILC patients (25/38), had lesions with FES high/FDG low uptake, consistent with the strongly ER + indolent nature of ILC. Patients with disease classified as FES high/FDG low had longer median overall survival (OS) (3.2 years) and progression-free survival (PFS) (1.5 years) than FES high/FDG high (OS = 2.1 years and PFS = 0.46 years). The median overall OS for all patients was 3.0 years (95% CI 2.5, 4.8) and PFS of 1.3 years (95% CI 0.6, 2.5). 8 patients (21%) had qualitatively more extensive disease by FES-PET.
Conclusions: Our findings suggest that both FES-PET and FDG-PET can identify metastatic ILC and be useful in detecting the pattern and extent of disease. The imaging combination provides additional information for prognosis and clinical decision making, balancing suitability for endocrine therapy and aggressiveness/indolence of disease.
Keywords: FDG; FES; Lobular breast cancer.
© 2025. The Author(s).