PET/CT imaging for tumour response assessment to immunotherapy: current status and future directions

Abstract

Recent immunotherapeutic approaches have evolved as powerful treatment options with high anti-tumour responses involving the patient’s own immune system. Passive immunotherapy applies agents that enhance existing anti-tumour responses, such as antibodies against immune checkpoints. Active immunotherapy uses agents that direct the immune system to attack tumour cells by targeting tumour antigens. Active cellular-based therapies are on the rise, most notably chimeric antigen receptor T cell therapy, which redirects patient-derived T cells against tumour antigens. Approved treatments are available for a variety of solid malignancies including melanoma, lung cancer and haematologic diseases. These novel immune-related therapeutic approaches can be accompanied by new patterns of response and progression and immune-related side-effects that challenge established imaging-based response assessment criteria, such as Response Evaluation Criteria in Solid tumours (RECIST) 1.1. Hence, new criteria have been developed. Beyond morphological information of computed tomography (CT) and magnetic resonance imaging, positron emission tomography (PET) emerges as a comprehensive imaging modality by assessing (patho-)physiological processes such as glucose metabolism, which enables more comprehensive response assessment in oncological patients. We review the current concepts of response assessment to immunotherapy with particular emphasis on hybrid imaging with 18F-FDG-PET/CT and aims at describing future trends of immunotherapy and additional aspects of molecular imaging within the field of immunotherapy.

SMARCA4-deficient thoracic tumor detected by [18F]FDG PET/CT

“…[ 18 F]FDG PET/CT is expected to play an important role in the early diagnosis of this disease and will contribute to the improvement of its prognosis. Furthermore, the value of [ 18 F]FDG PET/CT in therapeutic assessment should be investigated and established as with other malignant tumors (Becker et al 2020 ; Unterrainer et al 2020 ).…”

PET/CT imaging for evaluation of multimodal treatment efficacy and toxicity in advanced NSCLC—current state and future directions

“…Thereafter, in an attempt to promote congruence, the RECIST working group proposed a consensus guideline-immune RECIST (iRECIST) based on RECIST 1.1 [25], and finally in 2018, the immune-modified RECIST (imRECIST) criteria designed to better encapsulate response to immunotherapy were proposed [26]. A summary of available CT-based criteria is presented in Table 1, see also analogously (Citation Reference [27]).…”

“…To summarize, several novel criteria for response assessment based on PET-imaging have been proposed and further refined with special emphasis on clinical phenomena that accompany immunotherapy. However, these criteria have to be incorporated into randomized, clinical trials to confirm their final validity in prospective settings and comprehensively foster wide-spread use of hybrid imaging (see Table 2), see also analogously (Citation Reference [27]).…”

“…Hence, additional functional imaging associated with a higher resolution for potential patient stratification into different prognostic groups helps define patients who might benefit from treatment modification or intensification. Please refer for more detailed literature [27].…”

Radiomics in immuno-oncology

“…PECRIT/PERCIMT criteria) and detect immune-related side effects. [17][18][19][20] Outside the scope of this review, it is believed that molecular imaging will prove undoubtedly helpful as the field of oncology moves towards precision medicine.…”