FDG-PET as a "metabolic biopsy" tool in non-lung lesions with indeterminate biopsy

The differentiation of benign versus malignant disease in a lesion identified on conventional imaging is a commonly encountered problem. Attempted biopsy is often unsuccessful or falsely reassuring and may lead to the patient being sent for more invasive and potentially morbid investigations. Having previously identified the value of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) in this circumstance in patients with lung lesions, our current aim was to investigate the role of FDG-PET in helping to identify more accurately those patients with malignant lesions outside the lung. FDG-PET scanning was performed in 50 patients; most had undergone unsuccessful biopsy of a lesion outside the lung, while in a smaller number no attempt at biopsy had been made as it had been considered too dangerous. Follow-up was by histology or, if this was unavailable, by clinical progress to death or a minimum of 12 months post scan. Visual and quantitative analysis was performed. On visual analysis, the positive and negative predictive values were 89% and 100%, respectively. On quantitative (SUV>2.5) analysis, positive and negative predictive values were 93% and 86%, respectively. A negative FDG-PET study in these circumstances virtually excludes malignancy and allows the patient to be reassured. A positive scan encourages the clinician to pursue further biopsy to confirm a histological diagnosis. FDG-PET therefore assists in deciding which patients need to undergo further investigation.