Molecular imaging biomarkers for immune checkpoint inhibitor therapy

Abstract

Immune checkpoint inhibitors (ICIs) have substantially changed the field of oncology over the past few years. ICIs offer an alternative treatment strategy by exploiting the patients' immune system, resulting in a T cell mediated anti-tumor response. These therapies are effective in multiple different tumor types. Unfortunately, a substantial group of patients do not respond to ICIs. Molecular imaging, using single-photon emission computed tomography (SPECT) and positron emission tomography (PET), can provide non-invasive whole-body visualization of tumor and immune cell characteristics and might support patient selection or response evaluations for ICI therapies. In this review, recent studies with ¹⁸F-fluorodeoxyglucose-PET imaging, imaging of immune checkpoints and imaging of immune cells will be discussed. These studies are until now mainly exploratory, but the first results suggest that molecular imaging biomarkers could have a role in the evaluation of ICI therapy.

Keywords: biomarkers; immune checkpoint inhibitor; immunotherapy.; molecular imaging; positron emitting tomography.

Figure 1

Comparison of ¹⁸F-FDG-PET and ⁸⁹Zr-atezolizumab-PET imaging. Maximum intensity projections of ¹⁸F-FDG-PET, 1 h after tracer injection (A) and ⁸⁹Zr-atezolizumab-PET, 7 days after tracer injection (B) of a 53 year old woman diagnosed with NSCLC. Both imaging modalities show uptake in multiple intra-pulmonary metastases. The ¹⁸F-FDG-PET scan shows physiological high uptake in the brain and excretion via the kidneys. At the moment of this scan the patient had a post-renal obstruction due to a kidney stone. The ⁸⁹Zr-atezolizumab-PET scan shows high uptake in the spleen (red arrow). The ¹⁸F-FDG-PET scan was performed 46 days prior to the ⁸⁹Zr-atezolizumab-PET scan. Both scans were scaled equally (0-8).