Retroperitoneal Inflammation Detected on FDG PET/CT in Patient on Long-Term Immunotherapy

A 68-year-old man with a history of pulmonary adenocarcinoma on maintenance pembrolizumab presented for surveillance imaging. F-18-FDG PET/CT demonstrated new ill-defined right retroperitoneal and presacral soft tissue stranding with associated FDG uptake suggestive of inflammation. Biopsy results revealed fibroadipose tissue with extensive lymphoplasmacytic inflammation concerning for immunotherapy-related toxicity. The patient was subsequently taken off pembrolizumab, which he had been on for approximately 3 years. Recognition of immunotherapy-related adverse effects and how they can manifest on F-18-FDG PET/CT is important for prompt cessation of treatment.

Automated summary

A 68-year-old man with a history of pulmonary adenocarcinoma on maintenance pembrolizumab presented with new soft tissue stranding and inflammation on F-18-FDG PET/CT, which were confirmed as immunotherapy-related toxicity on biopsy. He discontinued pembrolizumab, which he had been taking for 3 years. Recognizing immunotherapy-related adverse effects on F-18-FDG PET/CT is crucial for timely cessation of treatment.