Clinically important detection of infection as an 'incidental' finding during cancer staging using FDG-PET/CT

FDG-PET/CT is widely used in the management of a variety of malignancies with excellent overall accuracy, despite the potential for false positive results related to infection and inflammation.

As cancer patients can develop clinically inapparent infections, we evaluated the prevalence and nature of incidental findings reported to be suggestive of infections that had been identified during clinical cancer staging with FDG-PET/CT.

The study involved a retrospective analysis of 60 patients managed primarily at our facility from a total of 121 cases identified as having possible infection on clinical reporting of more than 4500 cancer staging investigations performed during the calendar year of 2008.

Occult infections were uncommon overall (≤1%), but most often because of pneumonia (31.6%), upper respiratory tract infections (21.1%) or wound infections (15.8%). Abnormal scans contributed to patients' management in 52.7% of cases. Two out of 13 patients whose scan abnormalities were not investigated further had worsening changes on repeated scan and one of these patients had clinical deterioration.

In patients with FDG-PET/CT scans suggestive of infection and in whom a final diagnosis could be reached, the positive predictive value for FDG-PET/CT scans was 89% suggesting that abnormal scans indicative of infection should be investigated further in this population.