Rapidly growing complex fibroadenoma with surrounding ductal hyperplasia mimics breast malignancy on serial F-18 FDG PET/CT imaging.

A 30-year-old woman was referred for an F-18 fluorodeoxyglucose (FDG) PET/CT to rule out lymphoma, and was found to have an incidental FDG-avid right breast nodule that grew significantly in size and FDG uptake on a subsequent scan, raising suspicion of a growing breast malignancy. Histologic evaluation showed a complex fibroadenoma with adenosis and surrounding ductal hyperplasia. Although variable F-18 FDG uptake in fibroadenomas has been described, a distinction between simple and complex fibroadenomas has not been made in the PET literature, even though complex fibroadenomas have a higher propensity to develop into malignancies. This case shows that a rapidly growing complex fibroadenoma can mimic a breast malignancy on serial F-18 FDG PET/CT scans, showing significant increase in both size and FDG-avidity on follow-up studies.