A Rare Pattern of Breast Cancer Recurrence on 18f-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography: Isolated Micronodules in Distant Adipose Tissues

Recurrence of an initially early breast cancer (EBC) occurring exclusively in subcutaneous adipose tissues without skin or distant organ involvement is uncommon. Such recurrence is challenging to diagnose because of its non-specific clinical presentation and imaging characteristics, yet its identification is essential for optimal patient management. In this context, we report the case of an asymptomatic 41years old patient treated 10 years earlier for early left breast cancer, who presented during follow-up with a slight but continuous increase of CA 15-3 levels. Conventional imaging was negative and initial 18F-FDG PET/CT demonstrated three micronodules in the subcutaneous fat, located at a distance from the mastectomy scare, showing no metabolic activity and considered indeterminate. Four months later, a follow-up FDG PET/CT performed for persistent elevation of the tumor markers, revealed progression of the subcutaneous nodules, with the appearance of a moderate-to-high FDG uptake, without any other pathological foci. These findings were suggestive of isolated metastatic relapse in the adipose tissue, which was confirmed histologically. This case is reported from a pedagogical perspective to illustrate and raise awareness of a rare pattern of breast cancer relapse on FDG PET.