Analysis of incidental focal hypermetabolic uptake in the breast as detected by 18F-FDG PET/CT: clinical significance and differential diagnosis

Background: With the widespread use of PET/CT, incidental hypermetabolic foci unrelated to the known malignancy have been described with increasing frequency. Purpose: To determine the frequency and clinical significance of incidental focal hypermetabolic uptake in the breast as detected by 18F-FDG PET/CT, and to explore factors differentiating benign and malignant breast uptake. Material and Methods: From January 2005 to June 2010, a total of 51,971 whole-body FDG PET/CT examinations were performed in our clinic. After excluding 7254 sets of PET/CT data from patients known to have breast cancer, we retrospectively identified patients showing incidental focal hypermetabolic activity in the breast. Of 44,717 PET/CT examinations conducted on 32,988 patients, we identified 131 patients with no previous known or suspected benign and malignant breast disease. The etiology, mean SUVmax and diameter of breast lesions were assessed. We also compared the presentation of the lesions on CT, mammography, and ultrasonography. Results: Of the 131 patients, 60 were histologically diagnosed with breast lesions, including 32 with malignant and 28 with benign lesions. An additional 11 patients were followed-up for more than 2 years and were clinically considered to have benign lesions. The remaining 60 patients who had neither histologic confirmation nor followed-up for more than 2 years were excluded. Therefore, 71 patients were finally included. The mean SUVmax of 39 benign lesions and 32 malignant lesions were 2.02 +/- 1.52 and 3.71 +/- 3.83, respectively (P = 0.0001). At a cut-off value of 2.3, the rate of malignancy and specificity of the mean SUVmax for differentiating benign and malignant breast lesions were 61.3%, 76.3, respectively. The CT data from PET/CT revealed that the mean diameters of benign and malignant lesions were 1.19 +/- 0.97 cm and 2.26 +/- 1.96 cm, respectively (P = 0.0009). Conclusion: Incidental focal 18F-FDG uptake in the breast as detected by PET/CT was indicative of malignancy in 45% of patients. Both mean SUVmax and diameter were greater for malignant than benign lesions.