Weight Loss as Indication for FDG PET/CT

499 Background: One in every four patients with a malignancy presents with non-organ specific symptoms, weight loss being the most common. Some consider FDG PET/CT to be a preferred diagnostic modality in subjects with non-specific symptoms and signs of cancer. However, the clinical value of FDG PET/CT in weight loss patients remains to be clarified. The study’s goal was to determine the performance and clinical value of FDG PET/CT in patients referred primarily for weight loss. Methods: The electronic chart of subjects with the words “weight loss” in their FDG PET/CT scan report from 2010-2017 from one academic center in Montreal, Canada were retrospectively reviewed. Of the 12,868 FDG PET/CT scans in the database, 244 (1.9%) in 242 unique subjects had weight loss as the leading indication. Exclusion criteria included ongoing active malignancy (excluding 6 subjects), technically inadequate FDG PET/CT scans (excluding 1 subject) and insufficient follow-up information (excluding 1 subject). Demographic and clinical data gathered included history of prior malignancy, secondary clinical indications, actual weight lost and timeline, FDG PET/CT scan results, other clinical and imaging investigations related to the weight loss and the cause of the weight loss. The FDG PET/CT scans were considered clinically helpful if they were true positive for the cause of weight loss (malignant or not) that other investigations (particularly CT) had missed or would have missed. They were considered clinically unhelpful if they were true negative. They were considered detrimental when they were false positive leading to additional investigations or false negative. Results: A total of 236 FDG PET/CT studies in 234 unique subjects were ultimately included. The average weight loss prior to the FDG PET/CT study was 26 pounds in 10 months. The average subject follow-up time post FDG PET/CT scan was 3 years and 5 months. The cause of weight loss was clinically occult (no cause of weight loss proposed in chart) in 117/236 (50%), clinically certain (definitive cause of weight loss proposed in chart) in 51/236 (22%) and clinically suspected (only possible cause of weight loss proposed in chart) in 68/236 (29%) of subjects. 21 subjects had weight loss due to cancer and 98 subjects had weight loss from a non-malignant etiology. The FDG PET/CT scans were 24/236 (10%) true positive, 38/236 (16%) false positive, 148/236 (63%) true negative and 14/236 (6%) false negative. Of note, 6 of the true positive FDG PET/CT scans contained ancillary false positive findings. In 5% of the negative FDG PET/CT scans due to limited chart information, it could not be said whether they were true negative or false negative. Of the true positive FDG PET/CT scans, 6 were clinically useful, detecting 4 malignant and 2 non-malignant causes of weight loss. Of the 44 FDG PET/CT scans with false positive findings, 26 were detrimental, leading to a total of 35 additional procedures (23 imaging procedures, 7 biopsies, 4 consults, 1 blood test), the most notable one being an opened lung biopsy. Discussion/Conclusions: FDG PET/CT appears to have limited value in assessing subjects with weight loss as the leading clinical indication, proving to be approximately 6-7 times more often detrimental than helpful (14 falsely negative and 26 falsely positive leading to additional investigations versus 6 clinically helpful).