Imaging of Neuroendocrine Tumors: Indications, Interpretations, Limits, and Pitfalls

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.

Diagnostic Approaches to Neuroendocrine Neoplasms of Unknown Primary Site

ABSTRACT

Neuroendocrine tumors (NETs) are relatively uncommon heterogeneous neoplasms arising from endocrine and neuronal origin cells showing highly variable clinical behavior. By the time these tumors are discovered, up to 14% of patients with histologically proven NETs have metastasis, with the liver as the most frequently affected organ. Sometimes, no known primary site can be identified via routine imaging. Neuroendocrine tumors of unknown origin carry a poorer prognosis (compared with metastatic NETs with a known primary site) because of a lack of tailored surgical intervention and appropriate medical therapy (eg, chemotherapy or targeted therapy). A multimethod approach is frequently used in the trial to accurately determine the primary site for NETs of unknown primary sites and may include clinical, laboratory, radiological, histopathological, and surgical data. New molecular techniques using the genomic approach to identify the molecular signature have shown promising results. Various imaging modalities include ultrasound, computed tomography (CT), dual-energy CT, magnetic resonance imaging, and functional and hybrid imaging (positron emission tomography/CT, positron emission tomography/magnetic resonance imaging); somatostatin receptor imaging with new tracers is frequently used in an attempt for localization of the primary site.

Neuroendocrine Tumors: Diagnostics

Neuroendocrine neoplasms (NEN) are rare tumors arising from neuroendocrine cells. NEN are ideally suited for a theragnostic approach due to their specific expression of somatostatin receptors (SSTR). SSTR imaging of NEN dates back to the 1980s, but has evolved recently due to the introduction of more sensitive SSTR PET radiotracers. SSTR PET is a primary imaging modality for identifying NEN and characterizing SSTR expression. SSTR PET is complementary to anatomic imaging for assessing tumor response to treatment. SSTR PET is mandated to determine eligibility for peptide receptor radionuclide therapy. Here, the role of imaging to aid management of NEN is reviewed.

Advancements in Neuroendocrine Neoplasms: Imaging and Future Frontiers

Neuroendocrine neoplasms (NENs) are a diverse group of tumors with varying clinical behaviors. Their incidence has risen due to increased awareness, improved diagnostics, and aging populations. The 2019 World Health Organization classification emphasizes integrating radiology and histopathology to characterize NENs and create personalized treatment plans. Imaging methods like CT, MRI, and PET/CT are crucial for detection, staging, treatment planning, and monitoring, but each of them poses different interpretative challenges and none are immune to pitfalls. Treatment options include surgery, targeted therapies, and chemotherapy, based on the tumor type, stage, and patient-specific factors. This review aims to provide insights into the latest developments and challenges in NEN imaging, diagnosis, and management.

Spectral Computed Tomography-Derived Iodine Content and Tumor Response in the Follow-Up of Neuroendocrine Tumors-A Single-Center Experience

Spectral computed tomography (SCT) allows iodine content (IC) calculation for characterization of hypervascularized neoplasms and thus might help in the staging of neuroendocrine tumors (NETs). This single-center prospective study analyzed the association between SCT-derived IC and tumor response in the follow-up of metastasized NETs. Twenty-six patients with a median age of 70 years (range 51-85) with histologically proven NETs and a total of 78 lesions underwent SCT for staging. Because NETS are rare, no primary NET types were excluded. Lesions and intralesional hotspots were measured in virtual images and iodine maps. Tumor response was classified as progressive or nonprogressive at study endpoint. Generalized estimating equations served to estimate associations between IC and tumor response, additionally stratified by lesion location. Most commonly affected sites were the lymph nodes, liver, pancreas, and bones. Median time between SCT and endpoint was 64 weeks (range 5-260). Despite statistical imprecision in the estimate, patients with higher IC in lymphonodular metastases had lower odds for disease progression (adjusted OR = 0.21, 95% CI: 0.02-2.02). Opposite tendencies were observed in hepatic and pancreatic metastases in unadjusted analyses, which vanished after adjusting for therapy and primary tumor grade.

Nomogram for preoperative estimation of histologic grade in gastrointestinal neuroendocrine tumors

BACKGROUND

The treatment strategies and prognosis for gastroenteropancreatic neuroendocrine tumors were associated with tumor grade. Preoperative predictive grading could be of great benefit in the selection of treatment options for patients. However, there is still a lack of effective non-invasive strategies to detect gastrointestinal neuroendocrine tumors (GI-NETs) grading preoperatively.

METHODS

The data on 147 consecutive GI-NETs patients was retrospectively collected from January 1, 2012, to December 31, 2019. Logistic regression was used to construct a predictive model of gastrointestinal neuroendocrine tumor grading using preoperative laboratory and imaging parameters.The validity of the model was assessed by area under the receiver operating characteristic curve (AUC), calibration curve, and decision curve analysis (DCA).

RESULTS

The factors associated with GI-NETs grading were age, tumor size, lymph nodes, neuron-specific enolase (NSE), hemoglobin (HGB) and sex, and two models were constructed by logistic regression for prediction. Combining these 6 factors, the nomogram was constructed for model 1 to distinguish between G3 and G1/2, achieving a good AUC of 0.921 (95% CI: 0.884-0.965), and the sensitivity, specificity, accuracy were 0.9167, 0.8256, 0.8630, respectively. The model 2 was to distinguish between G1 and G2/3, and the variables were age, tumor size, lymph nodes, NSE, with an AUC of 0.847 (95% CI: 0.799-0.915), and the sensitivity, specificity, accuracy were 0.7882, 0.8710, 0.8231, respectively. Two online web servers were established on the basis of the proposed nomogram to facilitate clinical use. Both models showed an excellent calibration curve through 1000 times bootstrapped dataset and the clinical usefulness were confirmed using decision curve analysis.

CONCLUSION

The model served as a valuable non-invasive tool for differentiating between different grades of GI-NETs, personalizing the calculation which can lead to a rational treatment choice.

Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects

A new era of precision diagnostics and therapy for patients with neuroendocrine neoplasms began with the approval of somatostatin receptor (SSTR) radiopharmaceuticals for PET imaging followed by peptide receptor radionuclide therapy (PRRT). With the transition from SSTR-based γ-scintigraphy to PET, the higher sensitivity of the latter raised questions regarding the direct application of the planar scintigraphy-based Krenning score for PRRT eligibility. Also, to date, the role of SSTR PET in response assessment and predicting outcome remains under evaluation. In this comprehensive review article, we discuss the current role of SSTR PET in all aspects of neuroendocrine neoplasms, including its relation to conventional imaging, selection of patients for PRRT, and the current understanding of SSTR PET-based response assessment. We also provide a standardized reporting template for SSTR PET with a brief discussion.

Clinical value of 68Ga-DOTA-SSTR PET/CT in the diagnosis and detection of neuroendocrine tumors of unknown primary origin: a systematic review and meta-analysis

BACKGROUND

The ability of ⁶⁸Ga-DOTA-SSTR to detect the primary sites of neuroendocrine tumors (NETs) remains undetermined, and the clinical benefit of this imaging agent is not clear.

PURPOSE

To evaluate the diagnostic accuracy of ⁶⁸Ga-DOTA-SSTR for carcinoma unknown primary (CUP) neuroendocrine tumors and to further analyze the detection rate of ⁶⁸Ga-DOTA-SSTR for primary and metastatic sites.

MATERIAL AND METHODS

A comprehensive literature search of PubMed/MEDLINE and ScienceDirect was performed in October 2019 in accordance with the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. We critically reviewed all studies based on the PICOS criteria. QUADAS-2 was used to evaluate the quality of the methodology of the included studies.

RESULTS

A total of 10 studies (484 patients, mean age = 56.6 ± 4.3 years) were included in the study. The pooled sensitivity and specificity of ⁶⁸Ga-DOTA-SSTR in identifying CUP-NETs were 82% and 55%, respectively. The area under the receiver operating characteristic curve was 69%. Regarding metastasis sites, ⁶⁸Ga-DOTA-SSTR found the most metastases in the liver (57.9%), followed by the lymph nodes (22.8%), bones (12.8%), lung (2.8%), and others (1.7%). The pooled detection rate of ⁶⁸Ga-DOTA-SSTR for CUP-NETs was 61%.

CONCLUSION

The present study demonstrated the high diagnostic sensitivity of ⁶⁸Ga-DOTA-SSTR for CUP-NETs. ⁶⁸Ga-DOTA-SSTR PET/CT was highly effective in locating the primary and metastatic sites of CUP-NETs.

Imaging neuroendocrine tumors: Characterizing the spectrum of radiographic findings

Neuroendocrine tumors (NET) are a group of neoplasms with neuroendocrine differentiation affecting a wide range of organs. Functional NETs present with symptoms due to the particular hormone produced. Functional NETs are usually small at diagnosis and therefore can be challenging to diagnose. In contrast, non-functioning NETs are generally larger and present with mass effect. Imaging plays an indispensable role in diagnosis, staging and management of patients with NETs. The optimal modality and technique for imaging of NETs depend on the location of primary and metastatic lesions. Regardless of the imaging modality, dynamic contrast-enhanced imaging is essential for evaluation of NETs. In general, CT scan is typically the primary imaging modality for evaluating NETs. MRI is used as a complementary modality, being superior to other modalities to assess liver metastasis. Nuclear medicine imaging is also widely used in NET assessment.

Impact of 68Ga-DOTATOC PET/CT in comparison to 111In-Octreotide SPECT/CT in management of neuro-endocrine tumors: A case report

RATIONALE

In the diagnostics of neuroendocrine tumors (NETs), scintigraphy and Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) with Indium-Octreotide occupy a prominent place.The introduction in clinical practice of Gallium-labelled somatostatin analogues (DOTA-TOC, DOTA-TATE, DOTA-NOC) for Positron Emission Tomography/Computed Tomography (PET/CT), significantly improved NETs diagnostics due to greater sensitivity and improved lesion detection in addition to better patient convenience and decreased radiation dose.

PATIENT CONCERNS

We report a case of a patient who was diagnosed with a neuroendocrine tumor of the ileocecal valve.

DIAGNOSES

Diagnosis was made by ultrasonography, CT, and colonoscopy. Hystology after surgery was G2 NET of ileo-cecal valve. Restaging was carried out by In-Octreotide SPECT/CT and, 1 month later, by Ga-DOTATOC PET/CT. F-FDG PET/C was also carried out.

INTERVENTIONS

Ga-DOTATOC PET/CT showed larger disease that modified disease management from surgery to medical treatment.

OUTCOMES

After an initial improvement in the patient clinical condition, the tumor caused a worsening with the appearance of ascites.

LESSONS

Ga-DOTA-conjugate PET/CT is appropriate in low and intermediate NET (Ki67 index respectively ≤3% and 3%-20%) characterized by better survival and better response after Peptide Receptor Radionuclide Therapy.F-FDG is mostly useful in high grade (G3) of disease, so that Ga-DOTA-conjugate SUV and F-FDG SUV have an opposite trend in relation to the tumor grade. Ga-DOTATOC PET/CT changes, as in our case, therapeutic management in about 40% of cases.

The multidisciplinary team for gastroenteropancreatic neuroendocrine tumours: the radiologist's challenge

Background

Gastroenteropancreatic neuroendocrine tumours (GEP-NETs) are a heterogeneous group of tumours. An effective diagnosis requires a multimodal approach that combines evaluation of clinical symptoms, hormonelevels, radiological and nuclear imaging, and histological confirmation. Imaging plays a critical role in NETs diagnosis, prognosis and management, so the radiologists are important members of the multidisciplinary team. During diagnostic work-up two critical issues are present: firstly the need to identify tumor presence and secondly to define the primary site and assess regional and distant metastases.

Conclusions

The most appropriate imaging technique depends on the type of neuroendocrine tumour and the availability of specialized imaging techniques and expertise. There is no general consensus on the most efficient imaging pathway, reflecting the challenge in reliably detection of these tumours.

Current Practices and Novel Techniques in the Diagnosis and Management of Neuroendocrine Tumors of Unknown Primary

Neuroendocrine tumors (NETs) comprise a heterogeneous group of neoplasms in which tumor staging/prognosis and response to treatments depend heavily on accurate and timely identification of the anatomic primary site or NET subtype. Despite recent technological advancements and use of multiple diagnostic modalities, 10% to 14% of newly diagnosed NETs are not fully characterized based on subtype or anatomic primary site. Inability to fully characterize NETs of unknown primary may cause delays in surgical intervention and limit potential treatment options. To address this unmet need, clinical validity and utility are being demonstrated for novel approaches that improve NET subtype or anatomic primary site identification. Functional imaging using Ga-radiolabeled DOTATATE positron emission tomography/computed tomography has been shown to overcome some false-positive and resolution issues associated with octreotide scanning and computed tomography/magnetic resonance imaging. Using a genomic approach, molecular tumor classification based on differential gene expression has demonstrated high diagnostic accuracy in blinded validation studies of different NET types and subtypes. Given the widespread availability of these technologies, we propose an algorithm for the workup of NETs of unknown primary that integrates these approaches. Including these technologies in the standard workup will lead to better NET subtype identification and improved treatment optimization for patients.

Genetics and Epigenetics of Gastroenteropancreatic Neuroendocrine Neoplasms

Gastroenteropancreatic (GEP) neuroendocrine neoplasms (NENs) are heterogeneous regarding site of origin, biological behavior, and malignant potential. There has been a rapid increase in data publication during the last 10 years, mainly driven by high-throughput studies on pancreatic and small intestinal neuroendocrine tumors (NETs). This review summarizes the present knowledge on genetic and epigenetic alterations. We integrated the available information from each compartment to give a pathway-based overview. This provided a summary of the critical alterations sustaining neoplastic cells. It also highlighted similarities and differences across anatomical locations and points that need further investigation. GEP-NENs include well-differentiated NETs and poorly differentiated neuroendocrine carcinomas (NECs). NENs are graded as G1, G2, or G3 based on mitotic count and/or Ki-67 labeling index, NECs are G3 by definition. The distinction between NETs and NECs is also linked to their genetic background, as TP53 and RB1 inactivation in NECs set them apart from NETs. A large number of genetic and epigenetic alterations have been reported. Recurrent changes have been traced back to a reduced number of core pathways, including DNA damage repair, cell cycle regulation, and phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling. In pancreatic tumors, chromatin remodeling/histone methylation and telomere alteration are also affected. However, also owing to the paucity of disease models, further research is necessary to fully integrate and functionalize data on deregulated pathways to recapitulate the large heterogeneity of behaviors displayed by these tumors. This is expected to impact diagnostics, prognostic stratification, and planning of personalized therapy.

Type 1 Gastric Neuroendocrine Tumor Found on Endoscopic Polypectomy

Gastric neuroendocrine tumors (GNET) are rare gastric neoplasms accounting for <1% of all gastric neoplasms. The World Health Organization (WHO) categorized these neoplasms as types 1-3 to help predict malignant potential and long-term survival and guide management. Improved outcomes have been shown with endoscopic resections, but further studies are needed to confirm the best approach. We present a case of a 56-year-old woman who demonstrated the classic features of type one GNET with mucosal and submucosal involvement in the setting of primary atrophic gastritis, secondary hypergastrinemia, and underlying pernicious anemia. In general, standardizing treatment has been difficult due to a variable presentation.

PET/MR Imaging of the Pancreas

PET/MR imaging has the potential to markedly alter pancreatic care in both the malignant, and premalignant states with the ability to perform robust, high-resolution, quantitative molecular imaging. The ability of PET/MR imaging to monitor disease processes, potentially correct for motion in the upper abdomen, and provide novel biomarkers that may be a combination of MR imaging and PET biomarkers, offers a unique, precise interrogation of the pancreatic milieu going forward.