Predictive Value of FDG Uptake on PET for Future Immune Checkpoint Inhibitor-Mediated Colitis: A Case Series

Objectives: Immune-mediated colitis (IMC) is a common immune-related adverse event during immune checkpoint inhibitor (ICI) therapy. This case series and review aimed to highlight atypical cases of IMC and explore the potential of PET/CT to predict imminent ICI colitis. Methods: Through a descriptive, retrospective study at a tertiary cancer center, we identified adult patients receiving ICIs for any cancer between 2010 and 2022 who also underwent PET/CT for routine cancer surveillance during this time. We included patients who had signs and symptoms of colitis and reviewed their surveillance PET/CT scans obtained 2 to 6 weeks before and up to 3 months after diagnosis. Results: For the 33 included patients, surveillance scans were reviewed in collaboration with a nuclear radiologist. A total of 17 patients (51.5%) received combination therapy, while 14 (42.4%) received anti-PD-1/PD-L1 monotherapy. While ICI therapy has a median duration of 6.5 months, most patients (72.7%) had negative surveillance PET/CT for colitis. Diarrhea and colitis severity were similar among those with positive and negative findings for colitis on surveillance PET/CT. The outcomes of colitis were similar, with an 81.8% resolution in patients with negative PET/CT and 71.4% in patients with positive PET/CT. Conclusions: PET/CT imaging did not appear to assist in predicting IMC. This may be due to the long interval between clinical IMC and surveillance PET/CT imaging. The continued use of clinical criteria combined with laboratory markers, e.g., lactoferrin and calprotectin, and endoscopy/histology will enable more accurate detection and timely treatment of IMC.