68Ga - FAPI PET/CT Unmasks Extensive Metastatic Invasive Lobular Breast Cancer when Conventional Imaging Falls Short

Abstract

Invasive lobular carcinoma (ILC) is the second most common breast carcinoma, accounting for 10% to 15% of invasive breast
carcinomas. ILC is more difficult to diagnose on breast imaging including mammography, ultrasound, and MRI. We report a
case of 39 year old female with newly diagnosed left breast ILC (ER+, PR+, HER2). Mammography revealed a single irregular
dense mass in the upper central quadrant. Conventional bone scintigraphy demonstrated no evidence of skeletal
metastases. However, whole-body ⁶⁸Ga FAPI PET/CT revealed a markedly different disease burden. This case highlights the
added diagnostic value of ⁶⁸Ga FAPI PET/CT in detecting the true extent of ILC, particularly when conventional imaging
appears limited.

Keywords: Lobular breast cancer; ⁶⁸Ga-FAPI PET/CT; Fibroblast activation protein; cancer-associated fibroblasts; FAPI PET/CT;
breast cancer