Mastopathic-type fibroadenoma and ductal adenoma of the breast with false-positive fluorodeoxyglucose positron emission tomography.

Positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) has been shown to be an effective and accurate diagnostic technique for breast cancer. However, benign breast lesions have also been reported to show a false-positive FDG uptake on PET. We present two cases of benign tumors that revealed FDG uptake on PET and were difficult to distinguish from breast cancer. A 46-year-old premenopausal woman noticed a mass in her right breast. Ultrasonography showed a hypoechoic mass with the size of 7.7 x 3.9 mm and an irregular shape in the right breast. PET demonstrated a focal accumulation of FDG with a maximum standardized uptake value (SUVmax) of 2.1. Excisional biopsy was performed, and ductal adenoma was diagnosed. In the second case, a 36-year-old premenopausal woman was pointed out as showing an abnormality in the left breast on screening mammography. Ultrasonography showed a hypoechoic mass of 1.5 x 1.2 cm in size in the left breast. The lesion was depicted as a mass with prominent enhancement on dynamic CT and a focal accumulation of FDG with SUV max of 3.5 on PET. It was diagnosed as fibroadenoma of mastopathic type histopathologically by excisional biopsy. The readers should be aware that these benign tumors may cause false-positive results on PET.