Diagnostic dilemmas in the diagnosis of breast cancer with PET/CT

1295 Learning Objectives We aim to review both benign and malignant findings on FDG PET/CT which can pose diagnostic dilemmas (e.g., false-negative or false-positive results) in the diagnosis of breast cancer. Positron emission tomography (PET) with fluorine 18 fluorodeoxyglucose (FDG) is a commonly performed exam for the diagnosis, staging, and restaging of various cancers. In women with breast cancer, the most common indications for PET/CT include staging, evaluation of therapeutic response, and monitoring for recurrence. In women undergoing PET/CT for non-breast malignancy, several studies have reported unexpected FDG-avid breast lesions with an incidence ranging from 0.82% to 6.3%. The specificity of FDG PET for differentiating benign from malignant disease has approached 90% in most studies. FDG, however, is not a tumor specific marker which can pose diagnostic dilemmas. Metabolic activity is commonly observed in a variety of physiologic conditions. Common benign lesions including infection, fat necrosis, and recent surgery or radiation can lead to false-positive results. Less common entities such as silicone granulomas can also accumulate FDG. Conversely, false-negative results can occur in certain histologic types of breast cancer such as lobular carcinoma and tubular carcinoma. Finally, unexpected malignant lesions from a different primary (e.g., lymphoma or melanoma) can mimic primary breast cancer on PET/CT. We aim to review principles of FDG PET/CT in conjunction with clinical examples of benign and malignant lesions to aid in the accurate interpretation of breast lesions.