E1515. Understanding Immunotherapy Response With Molecular Imaging
  1. Elliot Varney; University of Mississippi Medical Center
  2. John Overton; University of Mississippi Medical Center
  3. Elizabeth Kerby; University of Mississippi Medical Center
  4. Johnny Yang; University of Mississippi Medical Center
  5. Quinn Cottone; University of Mississippi Medical Center
  6. Zainab Ahmad; University of Mississippi Medical Center
  7. Candace Howard; University of Mississippi Medical Center
Immunotherapy has taken off in recent years and revolutionized clinical oncology, achieving clinical responses and outcomes that were previously unthinkable. In addition, immunotherapy has brought to light the concept of precision medicine targeting specific disease processes with a common goal - treating the disease while limiting further damage. However, a critical issue that has arisen and gained research traction is the understanding and monitoring of treatment response. Molecular imaging, namely PET/CT, stands at the forefront of this assessment, yet accurate assessment of response to these therapies is paramount to understand treatment success and failure as early as possible. Thus, there is a need to educate the diagnostician of the mechanisms, benefits, and pitfalls to assessing immunotherapy response with molecular imaging.

Educational Goals / Teaching Points
Introduction to immunotherapy and molecular imaging. Common techniques to assess treatment response. How treatment response is defined (atypical response, common response criteria, and a need for standardization). Benefits (detecting side effects before clinically apparent, availability for new PET/CT related biomarkers, and still good for staging re-staging and assessing complete response and significant progression). Pitfalls and challenges include (what are the common false positives/false negatives, imaging immunotherapy-related adverse events, and pseudoprogression and hyperprogression). Recent advances include the development of new approaches and new radiotracers.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Patterns on FDG-PET/CT can differ between immunotherapy and conventional chemotherapy. The most common of these include hyperprogression and pseudoprogression. Hyperprogression, reported in 7 - 10% of patients, denotes accelerated tumor growth rate after immunotherapy initiation. Although effective disease progression is more common, pseudoprogression can often confuse the interpreting physician. Pseudoprogression is the hypermetabolic flare-phenomenon caused by the initial T-cell tumor infiltration most commonly seen with anti-CLTA4 and PD-1 agents. Both phenomena can be confused for one or the other, and evaluation of immunotherapeutic response is often difficult. Knowledge of the common adverse events, their inciting drugs, timing of therapy, and the typical clinical and imaging patterns of these effects is essential to accurately assess treatment response on FDG-PET/CT after immunotherapy.

The rise of immunotherapy agents available for treatment of cancer has revolutionized medical oncology, achieving improved clinical responses and outcomes. However, there are important differences in the appearance of surveillance imaging and unique pitfalls with immunotherapy agents after treatment. It is incumbent on the diagnostic radiologist reading these surveillance examinations to become familiar with these differences to provide a more accurate assessment of response.