Can benign lymphoid tissue changes in 18F-FDG PET/CT predict response to immunotherapy in metastatic melanoma?

Programmable Release of Chemotherapeutics from Ferrocene-Based Injectable Hydrogels Slows Melanoma Growth

Hydrogel-based injectable drug delivery systems provide temporally and spatially controlled drug release with reduced adverse effects on healthy tissues. Therefore, they represent a promising therapeutic option for unresectable solid tumor entities. In this study, a peptide-starPEG/hyaluronic acid-based physical hydrogel is modified with ferrocene to provide a programmable drug release orchestrated by matrix-drug interaction and local reactive oxygen species (ROS). The injectable ROS-responsive hydrogel (hiROSponse) exhibits adequate biocompatibility and biodegradability, which are important for clinical applications. HiROSponse is loaded with the two cytostatic drugs (hiROSponsedox/ptx) doxorubicin (dox) and paclitaxel (ptx). Dox is a hydrophilic compound and its release is mainly controlled by Fickian diffusion, while the hydrophobic interactions between ptx and ferrocene can control its release and thus be regulated by the oxidation of ferrocene to the more hydrophilic state of ferrocenium. In a syngeneic malignant melanoma-bearing mouse model, hiROSponsedox/ptx slows tumor growth without causing adverse side effects and doubles the relative survival probability. Programmable release is further demonstrated in a tumor model with a low physiological ROS level, where dox release, low dose local irradiation, and the resulting ROS-triggered ptx release lead to tumor growth inhibition and increased survival.

Immuno-metabolic reprogramming of T cell: a new frontier for pharmacotherapy of Rheumatoid arthritis

Rheumatoid arthritis (RA) is a persistent autoimmune condition characterized by ongoing inflammation primarily affecting the synovial joint. This inflammation typically arises from an increase in immune cells such as neutrophils, macrophages, and T cells (TC). TC is recognized as a major player in RA pathogenesis. The involvement of HLA-DRB1 and PTPN-2 among RA patients confirms the TC involvement in RA. Metabolism of TC is maintained by various other factors like cytokines, mitochondrial proteins & other metabolites. Different TC subtypes utilize different metabolic pathways like glycolysis, oxidative phosphorylation and fatty acid oxidation for their activation from naive TC (T0). Although all subsets of TC are not deleterious for synovium, some subsets of TC are involved in joint repair using their anti-inflammatory properties. Hence artificially reprogramming of TC subset by interfering with their metabolic status poised a hope in future to design new molecules against RA.

PET/Computed Tomography Transformation of Oncology: Immunotherapy Assessment

Immunotherapy approaches have changed the treatment landscape in a variety of malignancies with a high anti-tumor response. Immunotherapy may be associated with novel response and progression patterns that pose a substantial challenge to the conventional criteria for assessing treatment response, including response evaluation criteria in solid tumors (RECIST) 1.1. In addition to the morphologic details provided by computed tomography (CT) and MRI, hybrid molecular imaging emerges as a comprehensive imaging modality with the capacity to interrogate pathophysiological mechanisms like glucose metabolism. This review highlights the current status of 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) in prognostication, response monitoring, and identifying immune-related adverse events. Furthermore, it investigates the potential role of novel immuno-PET tracers that could complement the utilization of 18F-FDG PET/CT by imaging the specific pathways involved in immunotherapeutic strategies.

Can physiologic colonic [18F]FDG uptake in PET/CT imaging predict response to immunotherapy in metastatic melanoma?

AIM

The development of biomarkers that can reliably and early predict response to immune checkpoint inhibitors (ICIs) is crucial in melanoma. In recent years, the gut microbiome has emerged as an important regulator of immunotherapy response, which may, moreover, serve as a surrogate marker and prognosticator in oncological patients under immunotherapy. Aim of the present study is to investigate if physiologic colonic [18F]FDG uptake in PET/CT before start of ICIs correlates with clinical outcome of metastatic melanoma patients. The relation between [18F]FDG uptake in lymphoid cell-rich organs and long-term patient outcome is also assessed.

METHODOLOGY

One hundred nineteen stage IV melanoma patients scheduled for immunotherapy with ipilimumab, applied either as monotherapy or in combination with nivolumab, underwent baseline [18F]FDG PET/CT. PET/CT data analysis consisted of standardized uptake value (SUV), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) calculations in the colon as well as measurements of the colon-to-liver SUV ratios (CLRmean, CLRmax). Visual grading of colon uptake based on a four-point scale was also performed. Moreover, the spleen-to-liver SUV ratios (SLRmean, SLRmax) and the bone marrow-to-liver SUV ratios (BLRmean, BLRmax) were calculated. We also measured serum lipopolysaccharide (LPS) levels as a marker for bacterial translocation and surrogate for mucosal defense homeostasis. The results were correlated with patients' best clinical response, progression-free survival (PFS), and overall survival (OS) as well as clinical signs of colitis.

RESULTS

Median follow-up [95%CI] from the beginning of immunotherapy was 64.6 months [61.0-68.6 months]. Best response to treatment was progressive disease (PD) for 60 patients, stable disease (SD) for 37 patients, partial response (PR) for 18 patients, and complete response (CR) for 4 patients. Kaplan-Meier curves demonstrated a trend for longer PFS and OS in patients with lower colonic SUV and CLR values; however, no statistical significance for these parameters as prognostic factors was demonstrated. On the other hand, patients showing disease control as best response to treatment (SD, PR, CR) had significantly lower colonic MTV and TLG than those showing PD. With regard to lymphoid cell-rich organs, significantly lower baseline SLRmax and BLRmax were observed in patients responding with disease control than progression to treatment. Furthermore, patients with lower SLRmax and BLRmax values had a significantly longer OS when dichotomized at their median. In multivariate analysis, PET parameters that were found to significantly adversely correlate with patient survival were colonic MTV for PFS, colonic TLG for PFS, and BLRmax for PFS and OS.

CONCLUSIONS

Physiologic colonic [18F]FDG uptake in PET/CT, as assessed by means of SUV, before start of ipilimumab-based treatment does not seem to independently predict patient survival of metastatic melanoma. On the other hand, volumetric PET parameters, such as MTV and TLG, derived from the normal gut may identify patients showing disease control to immunotherapy and significantly correlate with PFS. Moreover, the investigation of glucose metabolism in the spleen and the bone marrow may offer prognostic information.

Imaging glucose metabolism to reveal tumor progression

Purpose: To analyze and review the progress of glucose metabolism-based molecular imaging in detecting tumors to guide clinicians for new management strategies. Summary: When metabolic abnormalities occur, termed the Warburg effect, it simultaneously enables excessive cell proliferation and inhibits cell apoptosis. Molecular imaging technology combines molecular biology and cell probe technology to visualize, characterize, and quantify processes at cellular and subcellular levels in vivo. Modern instruments, including molecular biochemistry, data processing, nanotechnology, and image processing, use molecular probes to perform real-time, non-invasive imaging of molecular and cellular events in living organisms. Conclusion: Molecular imaging is a non-invasive method for live detection, dynamic observation, and quantitative assessment of tumor glucose metabolism. It enables in-depth examination of the connection between the tumor microenvironment and tumor growth, providing a reliable assessment technique for scientific and clinical research. This new technique will facilitate the translation of fundamental research into clinical practice.

Positron emission tomography molecular imaging to monitor anti-tumor systemic response for immune checkpoint inhibitor therapy

Immune checkpoint inhibitors (ICIs) achieve a milestone in cancer treatment. Despite the great success of ICI, ICI therapy still faces a big challenge due to heterogeneity of tumor, and therapeutic response is complicated by possible immune-related adverse events (irAEs). Therefore, it is critical to assess the systemic immune response elicited by ICI therapy to guide subsequent treatment regimens. Positron emission tomography (PET) molecular imaging is an optimal approach in cancer diagnosis, treatment effect evaluation, follow-up, and prognosis prediction. PET imaging can monitor metabolic changes of immunocytes and specifically identify immuno-biomarkers to reflect systemic immune responses. Here, we briefly review the application of PET molecular imaging to date of systemic immune responses following ICI therapy and the associated rationale.

The other immuno-PET: Metabolic tracers in evaluation of immune responses to immune checkpoint inhibitor therapy for solid tumors

Unique patterns of response to immune checkpoint inhibitor therapy, discernable in the earliest clinical trials, demanded a reconsideration of the standard methods of radiological treatment assessment. Immunomonitoring, that characterizes immune responses, offers several significant advantages over the tumor-centric approach currently used in the clinical practice: 1) better understanding of the drugs' mechanism of action and treatment resistance, 2) earlier assessment of response to therapy, 3) patient/therapy selection, 4) evaluation of toxicity and 5) more accurate end-point in clinical trials. PET imaging in combination with the right agent offers non-invasive tracking of immune processes on a whole-body level and thus represents a method uniquely well-suited for immunomonitoring. Small molecule metabolic tracers, largely neglected in the immuno-PET discourse, offer a way to monitor immune responses by assessing cellular metabolism known to be intricately linked with immune cell function. In this review, we highlight the use of small molecule metabolic tracers in imaging immune responses, provide a view of their value in the clinic and discuss the importance of image analysis in the context of tracking a moving target.

Imaging assessment of toxicity related to immune checkpoint inhibitors

In recent years, a wide range of cancer immunotherapies have been developed and have become increasingly important in cancer treatment across multiple oncologic diseases. In particular, immune checkpoint inhibitors (ICIs) offer promising options to improve patient outcomes. However, a major limitation of these treatments consists in the development of immune-related adverse events (irAEs) occurring in potentially any organ system and affecting up to 76% of the patients. The most frequent toxicities involve the skin, gastrointestinal tract, and endocrine system. Although mostly manageable, potentially life-threatening events, particularly due to neuro-, cardiac, and pulmonary toxicity, occur in up to 30% and 55% of the patients treated with ICI-monotherapy or -combination therapy, respectively. Imaging, in particular computed tomography (CT), magnetic resonance imaging (MRI), and 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT), plays an important role in the detection and characterization of these irAEs. In some patients, irAEs can even be detected on imaging before the onset of clinical symptoms. In this context, it is particularly important to distinguish irAEs from true disease progression and specific immunotherapy related response patterns, such as pseudoprogression. In addition, there are irAEs which might be easily confused with other pathologies such as infection or metastasis. However, many imaging findings, such as in immune-related pneumonitis, are nonspecific. Thus, accurate diagnosis may be delayed underling the importance for adequate imaging features characterization in the appropriate clinical setting in order to provide timely and efficient patient management. ¹⁸F-FDG-PET/CT and radiomics have demonstrated to reliably detect these toxicities and potentially have predictive value for identifying patients at risk of developing irAEs. The purpose of this article is to provide a review of the main immunotherapy-related toxicities and discuss their characteristics on imaging.

Tumor metabolic and secondary lymphoid organ metabolic markers on 18F-fludeoxyglucose positron emission tomography predict prognosis of immune checkpoint inhibitors in advanced lung cancer

Background

The purpose of this study was to investigate the predictive value of tumor metabolic parameters in combination with secondary lymphoid metabolic parameters on positron emission tomography (PET)/computed tomography (CT) for immune checkpoint inhibitor (ICI) prognosis in advanced lung cancer.

Methods

This study retrospectively included 125 patients who underwent 18F-fludeoxyglucose (FDG) PET/CT before ICI therapy, including 41 patients who underwent a second PET/CT scan during ICI treatment. The measured PET/CT parameters included tumor metabolism parameters [maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), total lesion glycolysis (TLG), and total metabolic tumor volume (TMTV)] and secondary lymphoid organ metabolism parameters [spleen-to-liver SUVmax ratio (SLR) and bone marrow-to-liver SUVmax ratio (BLR)]. The correlation of PET/CT metabolic parameters with early ICI treatment response, progression-free survival (PFS), and overall survival (OS) was analyzed.

Results

Within a median follow-up of 28.7 months, there were 44 responders and 81 non-responders. The median PFS was 8.6 months (95% confidence interval (CI): 5.872–11.328), and the median OS was 20.4 months (95% CI: 15.526–25.274). Pretreatment tumor metabolic parameters were not associated with early treatment responses. The high bone marrow metabolism (BLR >1.03) was significantly associated with a shorter PFS (p = 0.008). Patients with a high TMTV (>168 mL) and high spleen metabolism (SLR >1.08) had poor OS (p = 0.019 and p = 0.018, respectively). Among the 41 patients who underwent a second PET/CT scan, the ΔSUVmax was significantly lower (p = 0.01) and the SLR was significantly higher (p = 0.0086) in the responders. Populations with low-risk characteristics (low TMTV, low SLR, and ΔSLR > 0) had the longest survival times.

Conclusion

High pretreatment TMTV and SLR are associated with poor OS, and increased spleen metabolism after ICI therapy predicts treatment benefit. This indicates that the combination of tumor and spleen metabolic parameters is a valuable prognostic strategy.

Differences and Similarities in the Pattern of Early Metabolic and Morphologic Response after Induction Chemo-Immunotherapy versus Induction Chemotherapy Alone in Locally Advanced Squamous Cell Head and Neck Cancer

Background: In head and neck cancer patients, parameters of metabolic and morphologic response of the tumor to single-cycle induction chemotherapy (IC) with docetaxel, cis- or carboplatin are used to decide the further course of treatment. This study investigated the effect of adding a double immune checkpoint blockade (DICB) of tremelimumab and durvalumab to IC on imaging parameters and their significance with regard to tumor cell remission. Methods: Response variables of 53 patients treated with IC+DICB (ICIT) were compared with those of 104 who received IC alone. Three weeks after one cycle, pathologic and, in some cases, clinical and endoscopic primary tumor responses were evaluated and correlated with a change in 18F-FDG PET and CT/MRI-based maximum-standardized uptake values (SUVmax) before (SUVmaxpre), after treatment (SUVmaxpost) and residually (resSUVmax in % of SUVmaxpre), and in maximum tumor diameter (Dmax) before (Dmaxpre) and after treatment (Dmaxpost) and residually (resD). Results: Reduction of SUVmax and Dmax occurred in both groups; values were SUVmaxpre: 14.4, SUVmaxpost: 6.6, Dmaxpre: 30 mm and Dmaxpost: 23 mm for ICIT versus SUVmaxpre: 16.5, SUVmaxpost: 6.4, Dmaxpre: 21 mm, and Dmaxpost: 16 mm for IC alone (all p < 0.05). ResSUVmax was the best predictor of complete response (IC: AUC: 0.77; ICIT: AUC: 0.76). Metabolic responders with resSUVmax ≤ 40% tended to have a higher rate of CR to ICIT (88%; n = 15/17) than to IC (65%; n = 30/46; p = 0.11). Of the metabolic nonresponders (resSUVmax > 80%), 33% (n = 5/15) achieved a clinical CR to ICIT versus 6% (n = 1/15) to IC (p = 0.01). Conclusions: ICIT and IC quickly induce a response and 18F-FDG PET is the more accurate modality for identifying complete remission. The rate of discrepant response, i.e., pCR with metabolic nonresponse after ICIT was >30%.

Adverse effects under immune checkpoint inhibitors on [18F]FDG PET/CT imaging

Despite their undisputed contribution to the management of various tumors and the prolongation of patient survival, immune checkpoint inhibitors (ICIs) exert their effect at the cost of toxicity. In the context of the activation of the host immune system triggered by ICIs, collateral, inflammatory side effects, commonly addressed as immune-related adverse events (irAEs) often occur. Early detection of irAEs can be critical for adequate decisions on patient management that may subsequently improve patient outcome. Moreover, the emergence of irAEs has been linked with the antitumor effect elicited by ICIs, thus, their identification may potentially provide prognostic information. Although the diagnosis of irAEs is mainly clinical, some adverse events may be asymptomatic and only diagnosed by imaging modalities. At the same time, radiological signs of irAEs are not necessarily associated with clinical symptoms, however, clinicians should be alerted to their presence. Among imaging modalities [¹⁸F]FDG PET/CT has shown satisfying efficiency in response assessment and monitoring of ICIs' treatment, especially in patients suffering from metastatic melanoma and lung cancer. In this context, [¹⁸F]FDG PET/CT may also be a valuable method for surveillance of irAEs during immunotherapy. This article aims to review the most common adverse events observed on [¹⁸F]FDG PET/CT under immunotherapy and summarize potential results linking PET signs of irAEs with response assessment to ICIs.

Joint EANM/SNMMI/ANZSNM practice guidelines/procedure standards on recommended use of [18F]FDG PET/CT imaging during immunomodulatory treatments in patients with solid tumors version 1.0

PURPOSE

The goal of this guideline/procedure standard is to assist nuclear medicine physicians, other nuclear medicine professionals, oncologists or other medical specialists for recommended use of [18F]FDG PET/CT in oncological patients undergoing immunotherapy, with special focus on response assessment in solid tumors.

METHODS

In a cooperative effort between the EANM, the SNMMI and the ANZSNM, clinical indications, recommended imaging procedures and reporting standards have been agreed upon and summarized in this joint guideline/procedure standard.

CONCLUSIONS

The field of immuno-oncology is rapidly evolving, and this guideline/procedure standard should not be seen as definitive, but rather as a guidance document standardizing the use and interpretation of [18F]FDG PET/CT during immunotherapy. Local variations to this guideline should be taken into consideration.

PREAMBLE

The European Association of Nuclear Medicine (EANM) is a professional non-profit medical association founded in 1985 to facilitate worldwide communication among individuals pursuing clinical and academic excellence in nuclear medicine. The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote science, technology and practical application of nuclear medicine. The Australian and New Zealand Society of Nuclear Medicine (ANZSNM), founded in 1969, represents the major professional society fostering the technical and professional development of nuclear medicine practice across Australia and New Zealand. It promotes excellence in the nuclear medicine profession through education, research and a commitment to the highest professional standards. EANM, SNMMI and ANZSNM members are physicians, technologists, physicists and scientists specialized in the research and clinical practice of nuclear medicine. All three societies will periodically put forth new standards/guidelines for nuclear medicine practice to help advance the science of nuclear medicine and improve service to patients. Existing standards/guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each standard/guideline, representing a policy statement by the EANM/SNMMI/ANZSNM, has undergone a thorough consensus process, entailing extensive review. These societies recognize that the safe and effective use of diagnostic nuclear medicine imaging requires particular training and skills, as described in each document. These standards/guidelines are educational tools designed to assist practitioners in providing appropriate and effective nuclear medicine care for patients. These guidelines are consensus documents based on current knowledge. They are not intended to be inflexible rules or requirements of practice, nor should they be used to establish a legal standard of care. For these reasons and those set forth below, the EANM, SNMMI and ANZSNM caution against the use of these standards/guidelines in litigation in which the clinical decisions of a practitioner are called into question. The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by medical professionals considering the unique circumstances of each case. Thus, there is no implication that an action differing from what is laid out in the guidelines/procedure standards, standing alone, is below standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the standards/guidelines when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources or advances in knowledge or technology subsequent to publication of the guidelines/procedure standards. The practice of medicine involves not only the science, but also the art of dealing with the prevention, diagnosis, alleviation and treatment of disease. The variety and complexity of human conditions make it impossible for general guidelines to consistently allow for an accurate diagnosis to be reached or a particular treatment response to be predicted. Therefore, it should be recognized that adherence to these standards/ guidelines will not ensure a successful outcome. All that should be expected is that practitioners follow a reasonable course of action, based on their level of training, current knowledge, clinical practice guidelines, available resources and the needs/context of the patient being treated. The sole purpose of these guidelines is to assist practitioners in achieving this objective. The present guideline/procedure standard was developed collaboratively by the EANM, the SNMMI and the ANZSNM, with the support of international experts in the field. They summarize also the views of the Oncology and Theranostics and the Inflammation and Infection Committees of the EANM, as well as the procedure standards committee of the SNMMI, and reflect recommendations for which the EANM and SNMMI cannot be held responsible. The recommendations should be taken into the context of good practice of nuclear medicine and do not substitute for national and international legal or regulatory provisions.

Interpretation of 2-[18F]FDG PET/CT in Hodgkin lymphoma patients treated with immune checkpoint inhibitors

The development of immunotherapy has revolutionized cancer treatment, improving the outcome and survival of many patients. Immune checkpoint inhibitors (ICIs), the most common form of immunotherapy, use antibodies to restore T-cells' anti-tumor activity. Immune checkpoint inhibitors are gaining ground in the therapeutic strategy across various cancers. Although widely used in solid tumors, ICIs have shown remarkable efficacy in patients with Hodgkin lymphoma. 2-[¹⁸F]Fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET)/CT is the gold standard to stage and monitor responses in Hodgkin lymphoma. This article reviewed the use of 2-[¹⁸F]FDG-PET/CT in patients with Hodgkin lymphoma treated with ICI, focusing on image interpretation for response monitoring and detecting adverse events. Key Points • Immune checkpoint inhibitors have dramatically improved the outcome of patients with cancer. Their mechanisms of action induce inflammatory processes that might translate into a high 2-[¹⁸F]FDG uptake visible on 2-[¹⁸F]FDG-PET/CT, requiring an adaptation of the evaluation criteria. • PET readers should be aware of new patterns of response observed with immunotherapy in assessing treatment response in HL patients. • -[¹⁸F]FDG-PET/CT has an unparalleled ability of assessing tumor response, visualizing signs of immune activation as well as immune-related adverse events in a one-stop-shop examination.

Immunotherapy Monitoring with Immune Checkpoint Inhibitors Based on [18F]FDG PET/CT in Metastatic Melanomas and Lung Cancer

Immunotherapy with checkpoint inhibitors has prompted a major change not only in cancer treatment but also in medical imaging. In parallel with the implementation of new drugs modulating the immune system, new response criteria have been developed, aiming to overcome clinical drawbacks related to the new, unusual, patterns of response characterizing both solid tumors and lymphoma during the course of immunotherapy. The acknowledgement of pseudo-progression, hyper-progression, immune-dissociated response and so forth, has become mandatory for all imagers dealing with this clinical scenario. A long list of acronyms, i.e., irRC, iRECIST, irRECIST, imRECIST, PECRIT, PERCIMT, imPERCIST, iPERCIST, depicts the enormous effort made by radiology and nuclear medicine physicians in the last decade to optimize imaging parameters for better prediction of clinical benefit in immunotherapy regimens. Quite frequently, a combination of clinical-laboratory data with imaging findings has been tested, proving the ability to stratify patients into various risk groups. The next steps necessarily require a large scale validation of the most robust criteria, as well as the clinical implementation of immune-targeting tracers for immuno-PET or the exploitation of radiomics and artificial intelligence as complementary tools during the course of immunotherapy administration. For the present review article, a summary of PET/CT role for immunotherapy monitoring will be provided. By scrolling into various cancer types and applied response criteria, the reader will obtain necessary information for better understanding the potentials and limitations of the modality in the clinical setting.

Assessment of early metabolic progression in melanoma patients under immunotherapy: an 18F-FDG PET/CT study

BACKGROUND

The usage of immune checkpoint inhibitors (ICIs) is the standard practice for the treatment of metastatic melanoma. However, a significant amount of patients show no response to immunotherapy, while issues on its reliable response interpretation exist. Aim of this study was to investigate the phenomenon of early disease progression in 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in melanoma patients treated with ICIs.

METHODS

Thirty-one patients under ICIs serially monitored with 18F-FDG PET/CT were enrolled. All patients exhibited progressive metabolic disease (PMD) after two ICIs' cycles according to the European Organization for Research and Treatment of Cancer (EORTC) criteria, and were characterized as unconfirmed PMD (uPMD). They were further followed with at least one PET/CT for either confirmation of PMD (cPMD) or demonstration of pseudoprogression remission. Patients were also evaluated with the PET Response Evaluation Criteria for Immunotherapy (PERCIMT). Moreover, in an attempt to investigate immune activation, the spleen to liver ratios (SLRmean, SLRmax) of 18F-FDG uptake were measured.

RESULTS

Median follow up was 69.7 months [64.6-NA]. According to EORTC, 26/31 patients with uPMD eventually showed cPMD (83.9%) and 5/31 patients showed pseudoprogression (16.1%). Patients with cPMD (n = 26) had a median OS of 10.9 months [8.5-NA], while those with pseudoprogression (n = 5) did not reach a median OS [40.9-NA]. Respectively, after application of PERCIMT, 2/5 patients of the pseudoprogression group were correctly classified as non-PMD, reducing the uPMD cohort to 29 patients; eventually, 26/29 patients demonstrated cPMD (89.7%) and 3/29 pseudoprogression (10.3%). One further patient with pseudoprogression exhibited transient, sarcoid-like, mediastinal/hilar lymphadenopathy, a known immune-related adverse event (irAE). Finally, patients eventually showing cPMD exhibited a significantly higher SLRmean than those showing pseudoprogression after two ICIs' cycles (p = 0.038).

CONCLUSION

PET/CT, performed already after administration of two ICIs' cycles, can identify the majority of non-responders in melanoma immunotherapy. In order to tackle however, the non-negligible phenomenon of pseudoprogression, another follow-up PET/CT, the usage of novel response criteria and vigilance over emergence of radiological irAEs are recommended. Moreover, the investigation of spleen glucose metabolism may offer further prognostic information in melanoma patients under ICIs.

Immune PET Imaging

Fluorodeoxyglucose (FDG) PET/CT is sensitive to metabolic, immune-related, and structural changes that can occur in tumors in cancer immunotherapy. Unique mechanisms of immune checkpoint inhibitors (ICIs) occasionally make response evaluation challenging, because tumors and inflammatory changes are both FDG avid. These response patterns and sequelae of ICI immunotherapy, such as immune-related adverse events, are discussed. Immune-specific PET imaging probes at preclinical stage or in early clinical trials, which may help guide clinical management of cancer patients treated with immunotherapy and likely have applications outside of oncology for other diseases in which the immune system plays a role, are reviewed.

Immune checkpoint inhibitor related adverse effects and FDG PET/CT findings

Immune check-point inhibitor (ICI) treatments activate the T-cells against tumor. Activated T-cells not only attack the tumor but also healthy cells, causing an autoimmune reaction in various tissues. These immune related adverse effects (IRAE) cause ¹⁸F-fluorodeoxyglucose (FDG) uptake in various tissues due to inflammation. It is important to recognize and report these findings on FDG Positron Emission Tomography/Computed Tomography (PET/CT) studies. FDG PET helps to determine the presence, location and severity of IRAEs. In severe cases, ICI treatments are interrupted or suspended and anti-inflammatory treatments are started. FDG uptake due IRAEs may mimic metastases or disease progression. Their presence may also help predicting response to treatment and have prognostic implications. In this review article, we will provide basic information about ICI treatments, IRAEs and FDG PET/CT findings.

Don't overlook spleen glucose metabolism on [18F]-FDG PET/CT for cancer drug discovery and development

Fluorine-18-fluorodeoxyglucose ([18F]-FDG) positron emission tomography/computed tomography (PET/CT) is a useful tool that assesses glucose metabolism in tumor cells to help guide management of cancer patients. However, the clinical relevance of glucose metabolism in healthy tissues, including hematopoietic tissues such as the spleen, has been potentially overlooked. Recent studies suggested that spleen glucose metabolism could improve the management of different cancers. Overall, the current literature includes 1,157 patients, with a wide range of tumor types. The prognostic and/or predictive value of spleen metabolism have been demonstrated in a broad spectrum of therapies including surgery and systemic cancer therapies. Most of these studies showed that high spleen glucose metabolism at baseline is associated with a poor outcome while treatment-induce change in spleen glucose metabolism is a multi-faceted surrogate of cancer-related inflammation, which correlates with immunosuppressive tumor microenvironment as well as with immune activation. In this systematic review, we seek to unravel the prognostic/predictive significance of spleen glucose metabolism on [18F]-FDG PET/CT and discuss how it could potentially guide cancer patient management in the future.

Quantitative Dynamic 18F-FDG PET/CT in Survival Prediction of Metastatic Melanoma under PD-1 Inhibitors

Simple Summary

The reliable and early during-the-course-of-treatment assessment of tumor response to the novel immunotherapeutic agents is a matter of debate, posing relevant challenges to conventional imaging modalities. In this prospective study, including 25 metastatic melanoma patients, we explored the prognostic significance of quantitative, dynamic ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) performed early during programmed cell death protein 1 (PD-1) blockade. At a median follow-up of 24.2 months, several semiquantitative and quantitative PET/CT parameters derived from tumor lesions and reference tissues had an impact on progression-free survival (PFS). In particular, ¹⁸F-FDG standardized uptake value (SUV_mean, SUV_max) and fractal dimension (FD) of melanoma lesions adversely affected PFS, while FD of the thyroid, as well as SUV_max and k₃ of the bone marrow, positively affected PFS. These findings underline the potential predictive role of quantitative, dynamic, interim PET/CT—performed in combination with conventional, static, whole-body PET/CT—in metastatic melanoma patients under PD-1 blockade.

Abstract

The advent of novel immune checkpoint inhibitors has led to unprecedented survival rates in advanced melanoma. At the same time, it has raised relevant challenges in the interpretation of treatment response by conventional imaging approaches. In the present prospective study, we explored the predictive role of quantitative, dynamic ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) performed early during immunotherapy in metastatic melanoma patients receiving treatment with programmed cell death protein 1 (PD-1) inhibitors. Twenty-five patients under PD-1 blockade underwent dynamic and static ¹⁸F-FDG PET/CT before the start of treatment (baseline PET/CT) and after the initial two cycles of therapy (interim PET/CT). The impact of semiquantitatively (standardized uptake value, SUV) and quantitatively (based on compartment modeling and fractal analysis) derived PET/CT parameters, both from melanoma lesions and different reference tissues, on progression-free survival (PFS) was analyzed. At a median follow-up of 24.2 months, survival analysis revealed that the interim PET/CT parameters SUV_mean, SUV_max and fractal dimension (FD) of the hottest melanoma lesions adversely affected PFS, while the parameters FD of the thyroid, as well as SUV_max and k₃ of the bone marrow positively affected PFS. The herein presented findings highlight the potential predictive role of quantitative, dynamic, interim PET/CT in metastatic melanoma under PD-1 blockade. Therefore, dynamic PET/CT could be performed in selected oncological cases in combination with static, whole-body PET/CT in order to enhance the diagnostic certainty offered by conventional imaging and yield additional information regarding specific molecular and pathophysiological mechanisms involved in tumor biology and response to treatment.

Incidence and Clinical Impact of Inflammatory Fluorodeoxyglucose Positron Emission Tomography Uptake After Neoadjuvant Pembrolizumab in Patients with Organ-confined Bladder Cancer Undergoing Radical Cystectomy

BACKGROUND

Data regarding the incidence and prognostic impact of immune-related imaging changes, assessed by ¹⁸[F] fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) scan, in patients receiving immune-checkpoint inhibitors (ICIs) are lacking. We relied on the population of patients enrolled in the PURE-01 study to evaluate such changes.

OBJECTIVE

To evaluate the role of PET/CT to visualize the immune-related adverse events (irAEs) following pembrolizumab.

DESIGN, SETTING, AND PARTICIPANTS

From February 2017 to August 2019, in 103 patients with nonmetastatic, clinical T2-4aN0M0 bladder cancer, PET/CT scan was performed before and after neoadjuvant pembrolizumab (N = 206 scans), before radical cystectomy.

INTERVENTION

PET/CT before and after neoadjuvant pembrolizumab, before radical cystectomy.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We analyzed the occurrence of irAEs, evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, against the development of inflammatory FDG uptake described at PET/CT (irAEs + PET/CT). Logistic regression analyses evaluated the association between irAEs + PET/CT and the pathological response to pembrolizumab. Kaplan-Meier curves tested their association with progression-free survival (PFS) after pembrolizumab and radical cystectomy.

RESULTS AND LIMITATIONS

Forty patients (39%) developed irAEs + PET/CT in several target organs. The most frequent target organs were the thyroid (N = 18), stomach (N = 14), mediastinal lymph nodes (N = 9), and lung (N = 5). These changes were clinically evident in 18 (45%) and were not associated with the pathological response, neither in terms of complete response (ypT0N0, p = 0.07) nor as downstaging to ypT≤1N0 disease (p = 0.1), although ypT0N0 responses were numerically more frequent in patients with irAEs+ PET/CT (47.5% vs 32%). Furthermore, irAE+ PET/CT events were associated with longer, not statistically significant, 24-mo PFS: 88.3% versus 76.5% (p = 0.5). Our results warrant further validation in larger datasets.

CONCLUSIONS

We presented unique surrogate data of PET/CT that could help improve our understanding of nonclinically evident effects of ICI administration, especially in patients at the early disease stage.

PATIENT SUMMARY

We evaluated the utility of PET/CT to visualize the occurrence of inflammatory changes after pembrolizumab in patients with localized bladder cancer without metastases. After immunotherapy, 39% of the patients developed ¹⁸[F] fluorodeoxyglucose uptake consistent of inflammatory changes. Overall, our data improve our knowledge on the effects induced by immunotherapy, which may have a clinical impact at longer follow-up. Take Home Message ● In the PURE-01 study, T2-4N0M0 muscle-invasive bladder cancer patients were staged with fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) before and after pembrolizumab. ● PET/CT after pembrolizumab revealed inflammatory FDG uptake in 39% of patients, but only 45% of these cases of uptake corresponded to clinically evident adverse events. ● The development of inflammatory uptake was associated with a higher pathological complete response rate and longer progression-free survival, although these differences were not statistically significant.

FDG PET/CT for Assessment of Immune Therapy: Opportunities and Understanding Pitfalls

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.

Impact of PET/CT for Assessing Response to Immunotherapy-A Clinical Perspective

Cancer immunotherapy using immune-checkpoint inhibitors (ICI) has revolutionized the therapeutic landscape of various malignancies like non-small-cell lung cancer or melanoma. Pre-therapy response prediction and assessment during ICI treatment is challenging due to the lack of reliable biomarkers and the possibility of atypical radiological response patterns. Positron emission tomography/computed tomography (PET/CT) enables the visualization and quantification of metabolic lesion activity additional to conventional CT imaging. Various biomarkers derived from PET/CT have been reported as predictors for response to ICI and may aid to overcome the challenges clinicians currently face in the management of ICI-treated patients. In this narrative review, experts in nuclear medicine, thoracic oncology, dermatooncology, hemato- and internal oncology, urological and head/neck tumors performed literature reviews in their respective field and a joint discussion on the use of PET/CT in the context of ICI treatment. The aims were to give a clinical overview on present standards and evidence, to identify current challenges and fields of research and to enable an outlook to future developments and their possible implications. Multiple promising studies concerning ICI response assessment or prediction using biomarkers derived from PET/CT alone or as composite biomarkers have been identified for various malignancies and disease stages. Of interest, additional major incentives in the field may evolve from novel tracers specifically targeting immune-checkpoint molecules which could allow not only response assessment and prognosis, but also visualization of histological tumor cell properties like programmed death-ligand (PD-L1) expression in vivo. Despite the broad range of existing literature on PET/CT-derived biomarkers in ICI therapy, implications for daily clinical practice remain elusive. High-quality prospective data are urgently warranted to determine whether patients benefit from the application of PET/CT in terms of prognosis. At the moment, the lack of such evidence as well as the absence of standardized imaging methods and biomarkers still precludes PET/CT imaging to be included in the relevant clinical practice guidelines.

Assessing Immunotherapy with Functional and Molecular Imaging and Radiomics

Immunotherapy is changing the treatment paradigm for cancer and has introduced new challenges in medical imaging. Because not all patients benefit from immunotherapy, pretreatment imaging should be performed to identify not only prognostic factors but also factors that allow prediction of response to immunotherapy. Follow-up studies must allow detection of nonresponders, without confusion of pseudoprogression with real progression to prevent premature discontinuation of treatment that can benefit the patient. Conventional imaging techniques and classic tumor response criteria are limited for the evaluation of the unusual patterns of response that arise from the specific mechanisms of action of immunotherapy, so advanced imaging methods must be developed to overcome these shortcomings. The authors present the fundamentals of the tumor immune microenvironment and immunotherapy and how they influence imaging findings. They also discuss advances in functional and molecular imaging techniques for the assessment of immunotherapy in clinical practice, including their use to characterize immune phenotypes, assess patient prognosis and response to therapy, and evaluate immune-related adverse events. Finally, the development of radiomics and radiogenomics in these therapies and the future role of imaging biomarkers for immunotherapy are discussed. Online supplemental material is available for this article. ^©RSNA, 2020.

Increased thyroid uptake on 18F-FDG PET/CT is associated with the development of permanent hypothyroidism in stage IV melanoma patients treated with anti-PD-1 antibodies

PURPOSE

To determine performances of 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) positron emission tomography (PET) to detect the development of permanent thyroid dysfunction (PTD), and to evaluate the prognostic value of early increased thyroid uptake in stage IV melanoma patients treated with anti-programmed death 1 (anti-PD-1) antibodies.

METHODS

Twenty-nine patients were retrospectively enrolled. PTD was defined as symptomatic thyroid disorder requiring long-term specific treatment. On the first PET performed during follow-up, maximal standardized uptake value of the thyroid (SUVmax-Th) and SUVmax-Th/SUVmax-blood-pool ratio (Th/B) were measured. Areas under ROC curves (AUC) of these parameters for the diagnostic of PTD were compared. Cutoff values were defined to maximize the Youden's index. Survival analyses were performed according to the Kaplan-Meier method and compared using the log-rank method between patients with and without enhanced thyroid uptake according to cutoff values defined with the Hothorn and Lausen method.

RESULTS

Four patients presented PTD. Median SUVmax-Th and Th/B were, respectively, 2.11 and 1.00. The median follow-up period was 21.7 months. AUC were 1.0 (CI_95% 0.88-1.0) for both parameters. Optimal cutoff values were, respectively, SUVmax-Th > 4.1 and Th/B > 2.0, both conferring sensitivities of 100% (CI_95% 40-100%) and specificities of 100% (CI_95% 86-100%). The median progression-free survival and overall survival were 11.3 months and 33.5 months, respectively. Using optimized cutoffs, there was no statistically significant difference of survival.

CONCLUSION

SUVmax-Th > 4.1 and Th/B > 2.0 provided perfect diagnostic performances to detect patients that developed PTD. No significant survival difference was found between patients with and without increased thyroid uptake.

The value of 18F-FDG PET/CT for predicting or monitoring immunotherapy response in patients with metastatic melanoma: a systematic review and meta-analysis

PURPOSE

To investigate the ability of ¹⁸F-FDG PET/CT to assess the response of patients with metastatic melanoma to immunotherapy.

METHODS

A comprehensive search of the literature for studies examining the prognostic value of ¹⁸F-FDG PET/CT in monitoring the response of patients with metastatic melanoma to immunotherapy was performed. We also screened the references of the selected articles to identify any other relevant studies. Detailed data were extracted and categorized. Comprehensive meta-analysis software was used for analysis.

RESULTS

Twenty four eligible articles were included in the systematic review. Based on the baseline ¹⁸F-FDG PET/CT imaging, the pooled hazard ratios of MTV, SLR, SUV/SULmax, SUV/SULpeak, and TLG for overall survival (OS) were 1.777 (95%CI: 1.389-2.275, p < 0.001), 3.425 (95%CI: 1.707-6.869, p = 0.001), 0.941 (95%CI: 0.599-1.477, p = 0.791), 1.704 (95%CI: 1.253-2.316, p = 0.016), and 1.755 (95%CI: 1.315-2.342, p < 0.001), respectively. The conventional and modified response assessment criteria exhibited a pooled sensitivity of 64% (95%CI: 46-79%) and 94% (95%CI: 81-99%) and a pooled specificity of 80% (95%CI: 59-93%) and 84% (95%CI: 64-95%), respectively, for the early ¹⁸F-FDG PET/CT scan. On the other hand, based on the late ¹⁸F-FDG PET/CT scan, the pooled sensitivity of 67% (95%CI: 35-90%) and 92% (95%CI: 73-99%) and pooled specificity of 77% (95%CI: 56-91%) and 76% (95%CI: 50-93%) were observed for the conventional and modified criteria, respectively. PET-detectable immune-related adverse events (irAEs) were associated with the response to therapy.

CONCLUSIONS

The baseline SUVpeak, MTV, and TLG parameters represent promising predictors of the final response of metastatic melanoma patients to immunotherapy. Modified response assessment criteria are potentially an appropriate method for monitoring immunotherapy. irAEs are also valuable for predicting eventual clinical benefit of treatment.

18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography for Assessing Tumor Response to Immunotherapy in Solid Tumors: Melanoma and Beyond

The complexity of the immune response and diversity of targets challenges conventional conceptual frameworks used in selecting and monitoring treatment with immune check-point inhibitors. The limitations of anatomic imaging in assessing response have been recognized. Varying patterns of response have been recognized. These patterns have different implications for the continuation and duration of therapy. Evidence supporting the role of ¹⁸F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography as a prognostic biomarker and in characterizing response is presented. An added benefit of this approach is the ability to detect immune-related inflammatory reactions, often in advance of severe or life-threatening clinical manifestations.

Imaging the Cancer Immune Environment and Its Response to Pharmacologic Intervention, Part 1: The Role of 18F-FDG PET/CT

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.

Novel Nuclear Medicine Imaging Applications in Immuno-Oncology

The global immuno-oncology pipeline has grown progressively in recent years, leading cancer immunotherapy to become one of the main issues of the healthcare industry. Despite their success in the treatment of several malignancies, immune checkpoint inhibitors (ICIs) perform poorly in others. Again, ICIs action depends on such a multitude of clinico-pathological features, that the attempt to predict responders/long-responders with ad-hoc built immunograms revealed to be quite complex. In this landscape, the role of nuclear medicine might be crucial, with first interesting evidences coming from small case series and pre-clinical studies. Positron-emission tomography (PET) techniques provide functional information having a predictive and/or prognostic value in patients treated with ICIs or adoptive T-cell therapy. Recently, a characterization of the tumor immune microenvironment (TiME) pattern itself has been shown to be feasible through the use of different radioactive tracers or image algorithms, thus adding knowledge about tumor heterogeneity. Finally, nuclear medicine exams permit an early detection of immune-related adverse events (irAEs), with on-going clinical trials investigating their correlation with patients’ outcome. This review depicts the recent advances in molecular imaging both in terms of non-invasive diagnosis of TiME properties and benefit prediction from immunotherapeutic agents.

Are immune-related adverse events associated with the efficacy of immune checkpoint inhibitors in patients with cancer? A systematic review and meta-analysis

BACKGROUND

A number of studies have reported an association between the occurrence of immune-related adverse events (irAEs) and clinical efficacy in patients undergoing treatment with immune checkpoint inhibitors (ICIs), but the results remain controversial.

METHODS

Under the guidance of a predefined protocol and Preferred Reporting Items for Systematic Reviews and Meta-analyses statement, this meta-analysis included cohort studies investigating the association of irAEs and efficacy of ICIs in patients with cancer. The primary outcome was overall survival (OS), and the secondary outcome was progression-free survival (PFS). Subgroup analyses involving the cancer type, class of ICIs, combination therapy, sample size, model, landmark analysis, and approach used to extract the data were performed. Specific analyses of the type and grade of irAEs were also performed.

RESULTS

This meta-analysis included 30 studies including 4971 individuals. Patients with cancer who developed irAEs experienced both an OS benefit and a PFS benefit from ICI therapy compared to patients who did not develop irAEs (OS: hazard ratio (HR), 0.54, 95% confidence interval (CI), 0.45-0.65; p < 0.001; PFS: HR, 0.52, 95% CI, 0.44-0.61, p < 0.001). Subgroup analyses of the study quality characteristics and cancer types recapitulated these findings. Specific analyses of endocrine irAEs (OS: HR, 0.52, 95% CI, 0.44-0.62, p < 0.001), dermatological irAEs (OS: HR, 0.45, 95% CI, 0.35-0.59, p < 0.001), and low-grade irAEs (OS: HR, 0.57, 95% CI, 0.43-0.75; p < 0.001) yielded similar results. The association between irAE development and a favorable benefit on survival was significant in patients with cancer who were undergoing treatment with programmed cell death-1 inhibitors (OS: HR, 0.51, 95% CI, 0.42-0.62; p < 0.001), but not cytotoxic T-lymphocyte antigen-4 inhibitors (OS: HR, 0.89, 95% CI, 0.49-1.61; p = 0.706). Additionally, the association was significant in patients with cancer who were treated with ICIs as a monotherapy (OS: HR, 0.53, 95% CI, 0.43-0.65; p < 0.001), but not as a combination therapy (OS: HR, 0.62, 95% CI, 0.36-1.05; p = 0.073).

CONCLUSIONS

The occurrence of irAEs was significantly associated with a better ICI efficacy in patients with cancer, particularly endocrine, dermatological, and low-grade irAEs. Further large-scale prospective studies are warranted to validate our findings.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019129310.

Immunotherapy by Immune Checkpoint Inhibitors and Nuclear Medicine Imaging: Current and Future Applications

Immunotherapy by using immune checkpoint inhibitors is a revolutionary development in oncology. Medical imaging is also impacted by this new therapy, particularly nuclear medicine imaging (also called radionuclide imaging), which uses radioactive tracers to visualize metabolic functions. Our aim was to review the current applications of nuclear medicine imaging in immunotherapy, along with their limitations, and the perspectives offered by this imaging modality. Method: Articles describing the use of radionuclide imaging in immunotherapy were researched using PubMed by April 2019 and analyzed. Results: More than 5000 articles were analyzed, and nearly 100 of them were retained. Radionuclide imaging, notably 18F-FDG PET/CT, already has a major role in many cancers for pre-therapeutic and therapeutic evaluation, diagnoses of adverse effects, called immune-related adverse events (IrAE), and end-of-treatment evaluations. However, these current applications can be hindered by immunotherapy, notably due to atypical response patterns such as pseudoprogression, which is defined as an increase in the size of lesions, or the visualization of new lesions, followed by a response, and hyperprogression, which is an accelerated tumor growth rate after starting treatment. To overcome these difficulties, new opportunities are offered, particularly therapeutic evaluation criteria adapted to immunotherapy and immuno-PET allowing us to predict responses to immunotherapy. Moreover, some new technological solutions are also promising, such as radiomic analyses and body composition on associated anatomical images. However, more research has to be done, notably for the diagnosis of hyperprogression and pseudoprogression. Conclusion: Immunotherapy, by its major impact on cancer and by the new patterns generated on images, is revolutionary in the field of medical images. Nuclear medicine imaging is already established and will be able to help meet new challenges through its plasticity.

Criteria of metabolic response to immunotherapy

Therapy response assessment is one of the most challenging indications of imaging studies. In clinical trial patients is usually measured with standardized response criteria. However, in the clinical practice, many studies are carried out in which the clinical question is whether or not the treatment is being effective. Answering this question is one of the greatest challenges for diagnostic imaging physicians, especially when a new treatment modality is being introduced, whose effects on tumoral lesions are firstly poorly understood. We have an essential role in the introduction of new therapies, assessing their effects and benefits. The knowledge of these effects has led to the development of many response criteria that, despite being applicable only in clinical trials, offer us information on how to interpret the findings in clinical practice.

Prognostic and theranostic 18F-FDG PET biomarkers for anti-PD1 immunotherapy in metastatic melanoma: association with outcome and transcriptomics

PURPOSE

An imaging-based stratification tool is needed to identify melanoma patients who will benefit from anti Programmed Death-1 antibody (anti-PD1). We aimed at identifying biomarkers for survival and response evaluated in lymphoid tissue metabolism in spleen and bone marrow before initiation of therapy.

METHODS

This retrospective study included 55 patients from two institutions who underwent 18F-FDG PET/CT before anti-PD1. Parameters extracted were SUVmax, SUVmean, HISUV (SUV-based Heterogeneity Index), TMTV (total metabolic tumor volume), TLG (total lesion glycolysis), BLR (Bone marrow-to-Liver SUVmax ratio), and SLR (Spleen-to-Liver SUVmax ratio). Each parameter was dichotomized using the median as a threshold. Association with survival, best overall response (BOR), and transcriptomic analyses (NanoString assay) were evaluated using Cox prediction models, Wilcoxon tests, and Spearman's correlation, respectively.

RESULTS

At 20.7 months median follow-up, 33 patients had responded, and 29 patients died. Median PFS and OS were 11.4 (95%CI 2.7-20.2) and 28.5 (95%CI 13.4-43.8) months. TMTV (>25cm³), SLR (>0.77), and BLR (>0.79) correlated with shorter survival. High TMTV (>25 cm3), SLR (>0.77), and BLR (>0.79) correlated with shorter survival, with TMTV (HR PFS 2.2, p = 0.02, and HR OS 2.5, p = 0.02) and BLR (HR OS 2.3, p = 0.04) remaining significant in a multivariable analysis. Low TMTV and TLG correlated with BOR (p = 0.03). Increased glucose metabolism in bone marrow (BLR) was associated with transcriptomic profiles including regulatory T cell markers (p < 0.05).

CONCLUSION

Low tumor burden correlates with survival and objective response while hematopoietic tissue metabolism correlates inversely with survival. These biomarkers should be further evaluated for potential clinical application.