Defining disease status in gastroenteropancreatic neuroendocrine tumors: Choi-criteria or RECIST?

Molecular Imaging for Response Assessment of Neuroendocrine Tumors (NET)

Assessing treatment response in neuroendocrine tumors (NET) remains a significant challenge due to their typically indolent growth and heterogenity, the frequent occurrence of disease stabilization rather than tumor shrinkage after therapy, and the inherent limitations of conventional imaging criteria. While molecular imaging-primarily somatostatin receptor (SST) PET/CT-has improved lesion detection, the absence of standardized response criteria limits its clinical utility and prevents its use as full replacement of conventional imaging. Emerging strategies, including revised thresholds for dimensional changes, criteria evaluating different features, such as lesions' density and functional tumor volumes, offer potential improvements in response evaluation but require further validation for routine clinical implementation. This review examines the current challenges in assessing NET treatment response, evaluates the strengths and limitations of available imaging modalities, and discusses emerging approaches and future directions for optimizing therapeutic monitoring in the heterogeneous panorama of NET.

PET- and CT-Based Imaging Criteria for Response Assessment of Gastroenteropancreatic Neuroendocrine Tumors Under Radiopharmaceutical Therapy

Despite well-documented limitations, current guidelines recommend the use of size-based RECIST 1.1 for response assessment of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) under radiopharmaceutical therapy (RPT). We hypothesize that functional criteria are superior to RECIST 1.1 for response assessment and progression-free survival (PFS) prediction, and molecular scores can be used in prognosticating PFS. Methods: This single-center, retrospective study included 178 patients with GEP-NETs (G1 and G2) who were treated with at least 2 consecutive cycles of RPT with [177Lu]Lu-DOTATATE and who underwent somatostatin receptor PET/CT at baseline and after 2 cycles of RPT (follow-up). PFS was defined as the time between baseline and clinical progression, as reported by a GEP-NET multidisciplinary tumor board (MDT) assessment or reported death. The differences in categorization and PFS between RECIST 1.1, Choi (functional criteria), and the MDT were evaluated, and 3-y PFS with MDT defined PFS as the reference. The predictive values of the different scores in somatostatin receptor standardized reporting and data system and Krenning (molecular scores) for PFS were analyzed. Results: Choi criteria classified a higher number of patients as having progressive disease and partial response and a lower number of patients as having stable disease compared with RECIST 1.1 (P < 0.01). The PFS of patients with progressive disease according to RECIST 1.1 and Choi criteria was shorter than that of patients with stable disease and partial response (P < 0.05). Choi criteria showed a nonsignificantly higher concordance with the MDT than with RECIST 1.1. There was a shift in category from a Krenning score of 4 to a score of 3 between baseline and follow-up (P < 0.01). At baseline, a Krenning score of 3 was associated with a shorter median PFS compared with a score of 4 (P < 0.05). Conclusion: In addition to RECIST 1.1, further PET- and CT-based imaging criteria have the potential to assess response and predict PFS in patients with GEP-NETs undergoing RPT. Our data support the assumption to use Choi criteria for prediction of PFS and agreement in response assessment. At baseline, the Krenning score can be used to predict therapy response after 2 cycles of RPT.

Assessment of response to PRRT including anatomical and molecular imaging as well as novel biomarkers

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for both oncological and hormone control and is a widely accepted standard of care treatment for patients with neuroendocrine neoplasms (NEN). Its use is anticipated to increase significantly, and this demands accurate tools and paradigms to assess treatment response post PRRT. This article outlines the current role and future developments of anatomical, molecular imaging and biomarkers for response assessment to PRRT, highlighting the challenges and provides perspectives for the need to focus on a multimodality, multidisciplinary and individualised approach for patients with this complex heterogeneous disease.

Circulating Chromogranin A as a Surveillance Biomarker in Patients with Carcinoids-The CASPAR Study

PURPOSE

Gastroenteropancreatic neuroendocrine tumors (GEP-NET) are relatively indolent but can be more aggressive. The current recommendations for using serum chromogranin A (CgA) for patients with GEP-NET are equivocal. This study was designed to validate an automated CgA immunofluorescence assay for monitoring disease progression in patients with GEP-NET.

PATIENTS AND METHODS

A prospective, multicenter, blinded observational study was designed to validate an automated CgA immunofluorescence assay for monitoring disease progression in patients with GEP-NET. Tumor progression was evaluated with RECIST 1.1 by CT/MRI. An increase ≥50% above the prior CgA concentration to a value >100 ng/mL in the following CgA concentration was considered positive.

RESULTS

A total of 153 patients with GEP-NET were enrolled. Using the prespecified cut-off of CgA change for tumor progression, specificity was 93.4% (95% confidence interval, 90.4%-95.5%; P < 0.001), sensitivity 34.4% (25.6%-44.3%), positive predictive value 57.9% (45.0-69.8), negative predictive value 84.3% (80.5-87.6), and AUC 0.73 (0.67-0.79).

CONCLUSIONS

Changes in serial measurements of serum CgA had a favorable specificity and negative predictive value, making this test a useful adjunct to routine radiographic monitoring.

Cylindrical TGR as early radiological predictor of RLT progression in GEPNETs: a proof of concept

This study aims to assess the predictive capability of cylindrical Tumor Growth Rate (cTGR) in the prediction of early progression of well-differentiated gastro-entero-pancreatic tumours after Radio Ligand Therapy (RLT), compared to the conventional TGR. Fifty-eight patients were included and three CT scans per patient were collected at baseline, during RLT, and follow-up. RLT response, evaluated at follow-up according to RECIST 1.1, was calculated as a percentage variation of lesion diameters over time (continuous values) and as four different RECIST classes. TGR between baseline and interim CT was computed using both conventional (approximating lesion volume to a sphere) and cylindrical (called cTGR, approximating lesion volume to an elliptical cylinder) formulations. Receiver Operating Characteristic (ROC) curves were employed for Progressive Disease class prediction, revealing that cTGR outperformed conventional TGR (area under the ROC equal to 1.00 and 0.92, respectively). Multivariate analysis confirmed the superiority of cTGR in predicting continuous RLT response, with a higher coefficient for cTGR (1.56) compared to the conventional one (1.45). This study serves as a proof of concept, paving the way for future clinical trials to incorporate cTGR as a valuable tool for assessing RLT response.

Imaging of Neuroendocrine Neoplasms; Principles of Treatment Strategies. What Referring Clinicians Want to Know

ABSTRACT

Neuroendocrine neoplasms (NENs) are a diverse group of tumors that express neuroendocrine markers and primarily affect the lungs and digestive system. The incidence of NENs has increased over time due to advancements in imaging and diagnostic techniques. Effective management of NENs requires a multidisciplinary approach, considering factors such as tumor location, grade, stage, symptoms, and imaging findings. Treatment strategies vary depending on the specific subtype of NEN. In this review, we will focus on treatment strategies and therapies including the information relevant to clinicians in order to undertake optimal management and treatment decisions, the implications of different therapies on imaging, and how to ascertain their possible complications and treatment effects.

Response heterogeneity as a new biomarker of treatment response in patients with neuroendocrine tumors

Aim: The RAISE project aimed to find a surrogate end point to predict treatment response early in patients with enteropancreatic neuroendocrine tumors (NET). Response heterogeneity, defined as the coexistence of responding and non-responding lesions, has been proposed as a predictive marker for progression-free survival (PFS) in patients with NETs. Patients & methods: Computerized tomography scans were analyzed from patients with multiple lesions in CLARINET (NCT00353496; n = 148/204). Cox regression analyses evaluated association between response heterogeneity, estimated using the standard deviation of the longest diameter ratio of target lesions, and NET progression. Results: Greater response heterogeneity at a given visit was associated with earlier progression thereafter: week 12 hazard ratio (HR; 95% confidence interval): 1.48 (1.20-1.82); p < 0.001; n = 148; week 36: 1.72 (1.32-2.24); p < 0.001; n = 108. HRs controlled for sum of longest diameter ratio: week 12: 1.28 (1.04-1.59); p = 0.020 and week 36: 1.81 (1.20-2.72); p = 0.005. Conclusion: Response heterogeneity independently predicts PFS in patients with enteropancreatic NETs. Further validation is required.

Appropriate use of morphological imaging for assessing treatment response and disease progression of neuroendocrine tumors

Neuroendocrine tumors (NETs) are relatively rare neoplasms displaying heterogeneous clinical behavior, ranging from indolent to aggressive forms. Patients diagnosed with NETs usually receive a varied array of treatments, including somatostatin analogs, locoregional treatments (ablation, intra-arterial therapy), cytotoxic chemotherapy, peptide receptor radionuclide therapy (PRRT), and targeted therapies. To maximize therapeutic efficacy while limiting toxicity (both physical and economic), there is a need for accurate and reliable tools to monitor disease evolution and progression and to assess the effectiveness of these treatments. Imaging morphological methods, primarily relying on computed tomography (CT) and magnetic resonance imaging (MRI), are indispensable modalities for the initial evaluation and continuous monitoring of patients with NETs, therefore playing a pivotal role in gauging the response to treatment. The primary goal of assessing tumor response is to anticipate and weigh the benefits of treatments, especially in terms of survival gain. The World Health Organization took the pioneering step of introducing assessment criteria based on cross-sectional imaging. This initial proposal standardized the measurement of lesion sizes, laying the groundwork for subsequent criteria. The Response Evaluation Criteria in Solid Tumors (RECIST) subsequently refined and enhanced these standards, swiftly gaining acceptance within the oncology community. New treatments were progressively introduced, targeting specific features of NETs (such as tumor vascularization or expression of specific receptors), and achieving significant qualitative changes within tumors, although associated with minimal or paradoxical effects on tumor size. Several alternative criteria, adapted from those used in other cancer types and focusing on tumor viability, the slow growth of NETs, or refining the existing size-based RECIST criteria, have been proposed in NETs. This review article aims to describe and discuss the optimal utilization of CT and MRI for assessing the response of NETs to treatment; it provides a comprehensive overview of established and emerging criteria for evaluating tumor response, along with comparative analyses. Molecular imaging will not be addressed here and is covered in a dedicated article within this special issue.