Clinical Significance of Incidental Finding of Focal Activity in the Breast at 18F-FDG PET/CT

The purpose of this study was to determine the clinical significance of the incidental finding of hypermetabolic foci in the breast at (18)F-FDG PET/CT in patients with malignant disease other than breast cancer or during a screening examination. The files of 13,897 women who underwent FDG PET/CT from November 2004 to October 2009 were retrospectively reviewed. Forty-eight patients with incidental breast uptake had undergone either tissue confirmation or clinical follow-up with additional sonographic imaging. The following four variables were evaluated: age, maximum standard uptake value (SUV(max)) of breast uptake at FDG PET, findings in the CT portion of PET/CT, and sonographic findings. Malignancy rates were calculated for each variable. Malignancy was diagnosed in 18 (37.5%) patients and a benign condition in 30 (62.5%) patients. Statistically significant differences in malignancy rate were found between the groups with SUV(max) less than 2 (24.2%) and the group with SUV(max) of 2 or greater (66.7%) and between the group with lesions in a BI-RADS ultrasound category lower than 4 (10.7%) and the group with lesions in category 4 or higher (75.0%) (p < 0.05). There was no significant difference in malignancy rates between the groups younger than 45 years (11.1%) and 45 years and older (53.3%) or between the group with lesions in a BI-RADS category lower than 4 (30.2%) and that with lesions in category 4 or higher (100%) on the CT portion of PET/CT. Incidental hypermetabolic foci in the breast may represent malignancy in as many as 37.5% of cases. The SUV(max) and sonographic findings can be useful for differentiating benign from malignant lesions.