Abstract
Immunotherapy agents are now entering the clinic in a wide array of malignancies and have provided a valuable addition to the therapeutic armamentarium. These agents enhance the global immune response by modulating the tumor microenvironment but can lead to unconventional patterns of response, challenging the conceptual framework that imaging is a robust surrogate for therapeutic efficacy. There is also increasing evidence that an effective antitumor response requires a systemic immune response in primary and secondary lymphoid tissues. However, an enhanced systemic immune response can lead to disruption of immunologic hemostasis in healthy tissues, causing adverse events. Better understanding of the complex interplay between tumoral and systemic immune response has been provided through tissue and liquid biopsy. However, the applicability of these methods is constrained by the biologic, spatial, and temporal heterogeneity of the processes involved. There is a growing interest in molecular imaging of cell-specific lineage markers of the immune system using biomolecules. However, the ongoing role of the more widely available 18F-FDG PET/CT for response assessment is being recognized through ongoing refinement of interpretative guidelines and emerging evidence. These noninvasive methods provide insights into the biologic basis of the global immune response to maximize potential therapeutic benefit. In this review, we aim to provide an overview of the current status of 18F-FDG PET/CT in the monitoring of tumoral and systemic immune response. In a companion review, the role of other imaging probes that might complement 18F-FDG PET/CT will be discussed.
Footnotes
Published online May 22, 2020.
Learning Objectives: On successful completion of this activity, participants should be able (1) to describe the importance of molecular imaging as a noninvasive method for monitoring of the tumor and systemic immune response to immunotherapy; (2) to recognize and differentiate the various conventional and unconventional patterns of tumor response to immune checkpoint inhibitors on 18F-FDG PET; and (3) to develop a framework for more accurate interpretation of 18F-FDG PET studies under immunotherapeutic strategies.
Financial Disclosure: The authors of this article have indicated no relevant relationships that could be perceived as a real or apparent conflict of interest.
CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credits. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, SAM, and other credit types, participants can access this activity through the SNMMI website (http://www.snmmilearningcenter.org) through July 2023.
- © 2020 by the Society of Nuclear Medicine and Molecular Imaging.