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E2065. Immunotherapy Adverse Effects on PET/CT Imaging: Important Points and Pitfalls
Authors
  1. Michael Goldenberg; Penn State College of Medicine
  2. Joseph Fotos; Penn State College of Medicine
Background
The advent of novel immunotherapeutic treatments has greatly improved outcomes for many malignancies by interfering with immune cell inhibition by tumor cells;(1) however, adverse effects of these treatments are not uncommon and can masquerade as other benign but serious pathologies.(2) In addition to true adverse effects of immunomodulatory medications, pseudoprogression of disease (i.e. an increase in total tumor burden [TTB] followed by disease decline) occurs in up to 9.7% of patients and appearance of new lesions followed by reduced TTB have been described.(2,3) With the widespread and repeated use of imaging to follow disease trajectory, particularly with 18F-FDG PET/CT, such confounding findings are often encountered. Thus, it is vital to accurately identify these changes and differentiate them from disease progression or another process so that proper treatment is initiated. Misidentification of false progression, for example, could result in unnecessary treatment of the patient or premature cessation of current therapy. Conversely, failure to identify true adverse effects may result in increased morbidity. The purpose of this exhibit is to describe common immunotherapeutic adverse effects, compare and contrast true disease progression with treatment-related changes, and qualify their distinctions.

Educational Goals / Teaching Points
The teaching points will describe various immunotherapy adverse events categorized by organ system and their imaging appearance. These will be compared to findings that may appear similar. There will also be discussion of findings of false progression attributed to immunomodulatory therapy. The goal is to help radiologists and clinicians recognize said entities, address them, and avoid misdiagnosis.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The findings will be broken down into two main categories: adverse reactions to immunomodulators and disease progression vs. false findings. The adverse reactions will further be broken down by organ system (e.g pneumonitis and sarcoid-like reaction in the lungs, thyroiditis in the head and neck, etc.). The images of disease progression will be contrasted with studies showing true disease progression.

Conclusion
As immunotherapy becomes a mainstay of successful cancer treatment, and its use expands to more and more malignancies, there will undoubtedly be more sightings of its adverse effects and false positive findings. It is critical for radiologists to differentiate among these findings to optimize patient care.