A Rare Case of Orbital Metastasis from Invasive Lobular Carcinoma: Challenges of 18F-FDG PET/CT and the Search for Consensus on Imaging.

Invasive lobular carcinoma (ILC) frequently underlies orbital metastasis. A 74-y-old woman, who was current with mammograms and had no cancer history, presented to her ophthalmologist with visual complaints and was found to have metastatic ILC. MRI was contraindicated, and an ¹⁸F-FDG PET/CT scan revealed a mildly hypermetabolic right orbital mass and low uptake in the left subareolar breast, suggestive of metastatic ILC. Small studies have found that in ILC, 16α-¹⁸F-fluoroestradiol and fibroblast activation protein inhibitors are more avid than ¹⁸F-FDG. There is currently no consensus regarding imaging for ILC. Many people have contraindications to MRI, and the higher rate of false-negative findings on mammography for ILC than for other breast cancers makes this patient population more vulnerable to inaccurate staging, incorrect assessment of tumor burden, and, consequently, insufficient treatment. We provide this interesting case to highlight the potential of ¹⁸F-fluoroestradiol PET/CT and fibroblast activation protein inhibitors over ¹⁸F-FDG in this breast cancer subtype.