Unexpected foci of 18F-FDG uptake in the breast detected by PET/CT: incidence and clinical significance.

Objective: The aim of this study was to evaluate the frequency and clinical significance of unexpected focal (18)F-fluorodeoxyglucose (FDG) uptake localized by PET/CT within the breast.

Methods: The files of 4,038 consecutive female cancer patients referred for FDG PET/CT over a period of 74 months were retrospectively reviewed. Patients with breast cancer were excluded from the study. The incidence of focal sites of increased FDG uptake localized by PET/CT to the breast was determined. The intensity of uptake was measured using the lean body mass maximum standard uptake value (LBM SUV(max)), and the presence and patterns of morphologic changes on CT were assessed. The etiology and clinical significance of findings were confirmed histologically or with imaging and clinical follow-up.

Results: Unexpected FDG foci in the breast were identified in 33 of 4,038 patients (0.82%). Follow-up data were available for 30 patients. Malignancy was diagnosed in 17 patients (histology 12, clinical 5) and excluded in 13 patients (histology 9, clinical 4). There was a borderline statistically significant difference in FDG uptake (LBM SUV(max)) between malignant (3.13 +/- 2.25) and benign (1.85 +/- 1.18) lesions (p = 0.05). Focal lesions were seen on CT in 23 patients (malignant 11, benign 12), and CT was negative in 7 patients (malignant 6, benign 1).

Conclusions: Although rare, incidental focal abnormal FDG uptake in the breast may represent malignant lesions in up to 57% of patients. Breast incidentalomas on PET/CT warrant further assessment including tissue sampling to define the etiology of these unexpected FDG-avid foci.