Immune checkpoint blockade has demonstrated the ability to modulate the immune system to produce durable responses in a wide range of
cancers and has significantly impacted the standard of care. However, many
cancer patients still do not respond to
immune checkpoint blockade or have a limited duration of antitumor responses. Moreover, immune-related adverse events caused by
immune checkpoint blockade can be severe and debilitating for some patients, limiting continuation of
therapy and resulting in severe autoimmune conditions. Standard-of-care conventional anatomic imaging modalities and
tumor response criteria have limitations to adequately assess
tumor responses, especially early in the course of
therapy, for risk-adapted clinical management to inform care of patients treated with
immunotherapy. Molecular imaging with position emission tomography (PET) provides a noninvasive functional
biomarker of
tumor response, and of immune activation, for patients on immune-based
therapies to help address these needs.
18F-FDG (FDG) PET/CT is readily available clinically and a number of studies have evaluated the use of this agent for assessment of prognosis, treatment response and immune activation for patients treated with
immune checkpoint blockade. In this review paper, we discuss the current oncologic applications and imaging needs of
cancer immunotherapy, recent studies applying FDG PET/CT for
tumor response assessment, and evaluation of immune-related adverse events for improving clinical management. We largely focus on metastatic
melanoma; however, we generalize where applicable to
immunotherapy in other
tumor types. We also briefly discuss PET imaging and quantitation as well as emerging non-FDG PET imaging radiotracers for
cancer immunotherapy imaging.