Clinical utility of 2-[18F] fluoro-2-deoxy-D-glucose positron emission tomography in predicting World Health Organization grade in pancreatic neuroendocrine tumors

Management of Gastric Neuroendocrine Tumors: A Review

Gastric neuroendocrine tumors (G-NET) are rare tumors arising from enterochromaffin-like cells of the gastric mucosa. They belong to a larger group called gastroenteropancreatic neuroendocrine tumors and are classified as low, intermediate, or high-grade tumors based on their proliferative indices. They are further categorized into three subtypes based on their morphologic characteristics, pathogenesis, and behavior. Types 1 and 2 tumors are characterized by elevated serum gastrin and are usually multifocal. They typically occur in the setting of atrophic gastritis or MEN1/Zollinger Ellison syndrome, respectively. Type 2 tumors are associated with the most symptoms, such as abdominal pain and diarrhea. Type 3 tumors are associated with normal serum gastrin, are usually solitary, and occur sporadically. This type has the most aggressive phenotype and metastatic potential. Treatment and prognosis for G-NET is dependent on their type, size, and stage. Type 1 has the best prognosis, and Type 3 has the worst. This review discusses the presentation, workup, and surgical management of these tumors.

Spatial and temporal heterogeneity of digestive neuroendocrine neoplasms

Neuroendocrine neoplasms (NENs) are initially monoclonal neoplasms that progressively become polyclonal, with very different genotypic and phenotypic characteristics leading to biological differences, including the Ki-67 proliferation index, morphology, or sensitivity to treatments. Whereas inter-patient heterogeneity has been well described, intra-tumor heterogeneity has been little studied. However, NENs present a high degree of heterogeneity, both spatially within the same location or between different lesions, and through time. This can be explained by the emergence of tumor subclones with different behaviors. These subpopulations can be distinguished by the Ki-67 index, but also by the expression of hormonal markers or by differences in the intensity of uptake on metabolic imaging, such as ⁶⁸Ga-somatostatin receptor and Fluorine-18 fluorodeoxyglucose positron emission tomography. As these features are directly related to prognosis, it seems mandatory to move toward a standardized, improved selection of the tumor areas to be studied to be as predictive as possible. The temporal evolution of NENs frequently leads to changes in tumor grade over time, with impact on prognosis and therapeutic decision-making. However, there is no recommendation regarding systematic biopsy of NEN recurrence or progression, and which lesion to sample. This review aims to summarize the current state of knowledge, the main hypotheses, and the main implications regarding intra-tumor spatial and temporal heterogeneity in digestive NENs.

Prognostic Value of 18F-FDG PET in Neuroendocrine Neoplasm: A Systematic Review and Meta-analysis

OBJECTIVES

Accurate assessment of the prognosis is critical for the rational treatment of neuroendocrine neoplasms (NENs). We performed a systematic review and meta-analysis of the prognostic value of 18F-FDG PET for NENs.

PATIENTS AND METHODS

PubMed and Embase databases were searched up to September 2020 for studies that evaluated 18F-FDG PET as prognostic factors in patients with NENs with overall survival (OS) and event-free survival (EFS) as outcomes. Hazards ratios (HRs) comparing high and low FDG uptakes were pooled using the DerSimonian-Laird method. Publication bias was assessed and adjusted for using the trim-and-fill method. Metaregression and subgroup analyses were performed to explore the cause of heterogeneity.

RESULTS

Twenty-three studies (1799 patients) were included. The overall pooled HRs of high FDG uptake on EFS and OS were 2.84 (95% confidence interval [CI], 2.21-3.64) and 3.50 (95% CI, 2.42-4.12), respectively. Publication biases were present regarding both EFS and OS (P = 0.0342 and 0.0009, respectively). After adjustment, effect sizes remained significant for EFS and OS (adjusted HR, 2.26 [95% CI, 1.76-2.89]; 3.16 [95% CI, 2.42-4.12]). In metaregression analyses, the proportion of grade 3 tumors positively correlated with the HR of OS (adjusted P = 0.0422).

CONCLUSIONS

18F-FDG PET is a significant prognostic factor in patients with NENs. 18F-FDG PET might be a useful prognostic biomarker in conjunction with the histologic grade and can help select the optimal treatment.

The diagnostic role of CT, MRI/MRCP, PET/CT, EUS and DWI in the differentiation of benign and malignant IPMN: A meta-analysis

PURPOSE

The objective of this study was to assess the diagnostic properties of computed tomography (CT), magnetic resonance imaging (MRI/MRCP) /Magnetic Resonance Cholangiopancreatography (MRCP), positron emission tomography/computed tomography (PET/CT), endoscopic ultrasound (EUS) and diffusion-weighted magnetic resonance imaging (DWI) in distinguishing benign and malignant intraductal papillary mucinous neoplasm (IPMN).

MATERIALS AND METHODS

Eligible databases were searched for eligible studies, published through July 2020 on the diagnostic accuracy of these modalities. Diagnostic accuracy parameters, including sensitivity, specificity, diagnostic odds ratio (DOR), and summary receiver operating characteristic curves (SROC) were calculated. Meta-regression was performed to identify the source of heterogeneity.

RESULTS

In total, 28 studies were included. Pooled sensitivities for CT, MRI/MRCP, PET/CT, EUS and DWI were 0.7, 0.76, 0.8, 0.6 and 0.72, respectively. Pooled specificities were 0.78, 0.83, 0.9, 0.8 and 0.97. The DORs were 8, 16, 35, 6 and 88. The areas under the curve (AUC) of SROC for CT, MRI/MRCP/MRCP, PET/CT, EUS and DW were 0.8, 0.87, 0.92, 0.79 and 0.82, respectively.

CONCLUSION

PET/CT showed the highest AUC and the overall diagnostic accuracy results support the use of MRI/MRCP, PET/CT interchangeably as a first-line examination in the diagnosis of malignant IPMN. With regard to DWI, EUS and CT, each techniques have their advantages and supportive to MRI/MRCP.

Ga-68 DOTA-peptides and F-18 FDG PET/CT in patients with neuroendocrine tumor: A review

OBJECTIVES

The aim of the present review was to assess the role of combined ¹⁸F-Fluorodeoxyglucose (F-18 FDG) and Ga-68 DOTA-peptides positron emission tomography (PET)-computed tomography (CT) in neuroendocrine tumors (NETs).

METHODS

We have searched MEDLINE databases, including PubMed and Scopus, for studies about the combined FDG and Ga-68 DOTA-peptides PET-CT or PET/Magnetic Resonance Imaging (MRI) in NETs in the last 15 years (from 2004 to November 2019). No limits were applied to the search strategy. Abstracts, reviews, letters to editors, and editorials were excluded.

RESULTS

Seven studies met the inclusion criteria. In total 236 patients received both ⁶⁸Ga-DOTA-peptides and F-18 FDG PET-CT for the characterization of NETs. In particular, 84 patients had a neuroendocrine lung tumor while the others mainly a gastroenteropancreatic NET. The combined use of F-18 FDG and Ga-68 DOTA-peptides (mainly TOC) PET studies provides complementary information regarding different biological characteristics of the lesions, thus enabling a more accurate selection of patients for targeted radionuclide therapy and a better stratification of the prognosis.

CONCLUSIONS

Ga-68 DOTA-peptides and F-18 FDG PET should be considered complementary in patients with NETs. They should be both performed in the initial staging and during follow-up, with a specific selection of patients and in a multidisciplinary vision.

Usefulness of 18 F-FDG-PET/CT in the diagnosis and prediction of recurrence of pancreatic neuroendocrine neoplasms

BACKGROUND

Although ¹⁸ F-FDG-PET/CT is a widely used diagnostic tool for several malignancies, its efficacy in diagnosing pancreatic neuroendocrine tumors is reported to be controversial because of the short-term follow-up.

METHODS

We retrospectively compared demographics and pathological features between ¹⁸ F-FDG-positive and -negative diseases. Additionally, we evaluated whether the avidity of ¹⁸ F-FDG-PET/CT affected earlier recurrence after curative treatment of non-functioning tumors. The median duration of observation was 65.6 months.

RESULTS

Seventy-two patients were enrolled. ¹⁸ F-FDG-positive diseases were pathologically advanced and significantly associated with metastatic behavior. In a multivariate analysis, metastatic behavior and WHO tumor grade was independently associated with ¹⁸ F-FDG accumulation. Only 25% of functional tumors (4/16) and 8% of insulinomas (1/12) were ¹⁸ F-FDG-positive. In a Kaplan-Meier analysis in patients with non-functioning tumors (n = 56), ¹⁸ F-FDG-positivity was significantly correlated with poorer recurrence-free survival (RFS) but had no correlation with overall survival. In univariate analysis of factors associated with shorter RFS, male gender, prevalence of nodal metastasis, WHO tumor grade ≥G2, or ¹⁸ F-FDG-positive disease were significantly higher in patients with shorter RFS, whereas only ¹⁸ F-FDG-positivity was associated with shorter RFS in multivariate analyses.

CONCLUSIONS

The avidity of ¹⁸ F-FDG-PET/CT was associated with metastatic behavior of pancreatic neuroendocrine tumors and recurrence after treatment of non-functioning tumors.

Value of Pretreatment 18F-fluorodeoxyglucose Positron Emission Tomography in Patients With Localized Pancreatic Cancer Treated With Neoadjuvant Therapy

Background:¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) imaging is not routine in patients with localized pancreatic cancer (PC). We evaluated the prognostic value of PET/CT in patients who received neoadjuvant therapy.

Methods: Patients with localized PC underwent pretreatment PET/CT with or without posttreatment (preop) PET/CT. Maximum standardized uptake values (SUV) were classified as high or low based on a cut point of 7.5 at diagnosis (SUV_dx) and 3.5 after neoadjuvant therapy (preoperative; SUV_preop). Preop carbohydrate antigen 19-9 (CA19-9) was classified as normal ( ≤ 35 U/mL) or elevated.

Results: Pretreatment PET/CT imaging was performed on 201 consecutive patients; SUV_dx was high in 98 (49%) and low in 103 (51%). Preop PET/CT was available in 104 (52%) of the 201 patients; SUV_preop was high in 60 (58%) and low in 44 (42%). Following neoadjuvant therapy, preop CA19-9 was normal in 90 (45%) patients and elevated in 111 (55%). Median overall survival (OS) of all patients was 27 months; 33 months for the 103 patients with a low SUV_dx and 22 months for the 98 patients with a high SUV_dx (p = 0.03). Median OS for patients with low SUV_dx/normal preop CA19-9, high SUV_dx/normal preop CA19-9, low SUV_dx/elevated preop CA19-9, and high SUV_dx/elevated preop CA19-9 were 66, 34, 23, and 17 months, respectively (p < 0.0001). OS was 44 months for the 148 (74%) patients who completed all intended neoadjuvant therapy and surgery and 13 months for the 53 (26%) who did not undergo surgery (p < 0.001).

Conclusion: Pretreatment PET/CT avidity and preop CA19-9 are clinically significant prognostic markers in patients with PC.

Lesion-by-lesion correlation between uptake at FDG PET and the Ki67 proliferation index in resected pancreatic neuroendocrine tumors

BACKGROUND

Ki67 proliferation index and tumor uptake on 18fluorodeoxyglucose positron-emitting tomography (FDG-PET) could be correlated in pancreatic neuroendocrine tumors (PanNET), but the evaluation of the former is subject to tumor heterogeneity.

AIMS

Explore the correlation between Ki67 and FDG-PET uptake at the lesion scale in PanNET.

METHODS

We identified target lesions ≥10 mm in patients operated on for a PanNET and/or associated metastases with preoperative FDG-PET and without neoadjuvant treatment. We assessed the lesion-by-lesion correlation between Ki67 and the tumor-to-liver SUVmax ratio (SUVmax T/L), and between pathological grade (G) and metabolic grade (mG) (mG1, SUVmax T/L ≤ 1, mG2, SUVmax T/L 1-2.3 and mG3, SUVmax T/L > 2.3).

RESULTS

Twenty-one patients underwent pancreatic (n = 12), liver (n = 2) or combined surgery (n = 7). Overall, 36 target lesions (21 primary PanNET, 13 liver metastases and 2 lymph-node metastases) were identified, of median Ki67 4%. Ki67 correlated with SUVmax T/L (r = 0.55, p < 0.001). Median SUVmax T/L was 0.76, 1.41 and 2.67 for lesions G1, G2 and G3, respectively (p = 0.005). Median Ki67 was 1, 4 and 25 for lesions mG1, mG2 and mG3, respectively (p = 0.005).

CONCLUSIONS

Uptake on FDG-PET could predict the pathological grade of PanNET lesions. Hence, FDG-PET could supplement pathological evaluation of tumor biological aggressiveness and could guide the choice of the most relevant lesions to biopsy.

Imaging of pancreatic neuroendocrine tumors: recent advances, current status, and controversies

INTRODUCTION

Recently, there have been a number of advances in imaging pancreatic neuroendocrine tumors (panNETs), as well as other neuroendocrine tumors (NETs), which have had a profound effect on the management and treatment of these patients, but in some cases are also associated with controversies. Areas covered: These advances are the result of numerous studies attempting to better define the roles of both cross-sectional imaging, endoscopic ultrasound, with or without fine-needle aspiration, and molecular imaging in both sporadic and inherited panNET syndromes; the increased attempt to develop imaging parameters that correlate with tumor classification or have prognostic value; the rapidly increasing use of molecular imaging in these tumors and the attempt to develop imaging parameters that correlate with treatment/outcome results. Each of these areas and the associated controversies are reviewed. Expert commentary: There have been numerous advances in all aspects of the imaging of panNETs, as well as other NETs, in the last few years. The advances are leading to expanded roles of imaging in the management of these patients and the results being seen in panNETs/GI-NETs with these newer techniques are already being used in more common tumors.

Value of diffusion-weighted magnetic resonance imaging in predicting World Health Organization grade in G1/G2 pancreatic neuroendocrine tumors

The present study aimed to investigate the value of diffusion-weighted magnetic resonance imaging (DWI) in the grading of well-differentiated pancreatic neuroendocrine tumors (PanNETs). A total of 44 patients with histologically proven well-differentiated PanNET [grade 1 (G1) and grade 2 (G2) according to the World Health Organization (WHO) criteria] underwent pretreatment magnetic resonance imaging (MRI), which was retrospectively analyzed. The location, size, cystic or solid appearance, boundary, presence or absence of tumor contrast enhancement, and MRI signal of the tumor were assessed. Apparent diffusion coefficients (ADCs) within the primary tumor were measured on ADC maps. Receiver operating characteristic curves were used to determine ADC cut-off values and the sensitivity and specificity of the grade prediction. Spearman's rank correlation was utilized to probe the association between ADC value and PanNET grade or pathological parameters. G1 tumors exhibited a well-circumscribed border more often than G2 tumors. No marked differences were observed between PanNET G1 and PanNET G2 for cystic or solid appearance, enhancement, and T1- and T2-weighted imaging signals. Marked hyperintensities were more common in PanNET G2 tumors than in PanNET G1 tumors (P<0.01). The mean ADC values were statistically different between the normal pancreas and G1 and G2 tumors (P<0.01), and between PanNET G1 and PanNET G2 (P<0.05). Correlation analysis showed that ADC value was negatively correlated with PanNET grade, mitotic count and Ki-67 proliferation index (P<0.05). The cut-off ADC value was 0.930×10^-3 mm²/sec, which identified G2 tumors with 82.4% sensitivity and 79.5% selectivity. ADC value therefore represents a non-invasive and valuable imaging parameter in predicting the WHO grade of tumors in well-differentiated PanNET.

Pancreatic neuroendocrine neoplasms at magnetic resonance imaging: comparison between grade 3 and grade 1/2 tumors

Background

The grading of pancreatic neuroendocrine neoplasms (PanNENs) is associated with the choice of treatment strategy. The aim of this study is to identify the magnetic resonance imaging (MRI) features in differentiating pancreatic neuroendocrine tumors (PanNETs) grade 1/2 (G1/G2) and pancreatic neuroendocrine carcinoma grade 3 (PanNEC G3).

Patients and methods

A total of 59 patients with histologically proven PanNENs and who underwent pretreatment MRI were retrospectively analyzed. Tumor location, size, boundary, cystic or solid appearance, enhancement degree, pancreatic duct dilatation, metastases and MRI signal were evaluated. Apparent diffusion coefficients (ADCs) were measured on ADC maps. Receiver operating characteristic curve was used to determine the cut off values and the sensitivity and specificity of prediction. Spearman correlation and logistic regression analysis were adopted to identify the association between MRI features and pathological parameters.

Results

A total of 47 lesions were PanNETs G1/G2 and 12 lesions were PanNEC G3. G1/G2 tumors were more common with well-circumscribed border compared with PanNEC G3. Ill- defined boundary, big size, necrosis, low-moderate enhancement, pancreatic duct dilatation, metastases and high diffusion-weighted imaging (DWI) intensity were more common in PanNEC G3 than in PanNETs G1/G2. The ADC values of PanNEC G3 were also significantly lower compared with the PanNETs G1/G2 and normal pancreatic parenchyma. The cut off value of ADC was 0.95×10⁻³ mm²/s for differentiating PanNEC G3 from PanNETs G1/G2 with 72.3% sensitivity and 91.6% specificity, respectively. Ki-67 index and mitosis count positively correlated with tumor size, pancreatic duct dilatation and metastases (P<0.05) and negatively correlated with ADC values (P<0.01), respectively. Regression analysis further showed that metastases and ADC value were associated with PanNENs grade.

Conclusion

Metastases and ADC value may have potential for differentiating PanNEC G3 from PanNETs G1/G2.

Role of Combined 68Ga-DOTATOC and 18F-FDG Positron Emission Tomography/Computed Tomography in the Diagnostic Workup of Pancreas Neuroendocrine Tumors: Implications for Managing Surgical Decisions

OBJECTIVES

Ga-DOTATOC (Ga) positron emission tomography (PET)/computed tomography (CT) is recommended in the workup of pancreas neuroendocrine tumors (PanNETs); evidence suggests that F-FDG (F) PET/CT can also provide prognostic information. Aims of this study were to assess the role of combined Ga- and F-PET/CT in the evaluation of grade (G) 1-2 PanNETs and to test the correlation between F-PET/CT positivity and tumor grade.

METHODS

Preoperative Ga- and F-PET/CT of 35 patients with surgically resected G1-2 PanNETs were evaluated. For grading, the 2010 World Health Organization Classification was used; an ancillary analysis with Ki67 cutoffs at 5% to 20% was conducted. Correlation between F-PET/CT positivity (SUVmax > 3.5) and grade was assessed.

RESULTS

Of 35 PanNETs, 28.6% and 71.4% were G1 and G2 as per World Health Organization. Ga-PET/CT showed high sensitivity (94.3%) in detecting G1-2 PanNETs. F-PET/CT was positive in 20% and 76% G1 and G2 tumors (P = 0.002). F-PET/CT identified G2 PanNETs with high positive predictive value (PPV, 90.5%). F-PET/CT correlated with tumor grade also in the ancillary analysis (P = 0.009).

CONCLUSIONS

The high sensitivity of Ga-PET/CT in NET detection is known. The high PPV of F-PET/CT in the identification of G2 forms suggests its potential role in PanNETs prognostication and risk stratification.

Shape and Enhancement Characteristics of Pancreatic Neuroendocrine Tumor on Preoperative Contrast-enhanced Computed Tomography May be Prognostic Indicators

BACKGROUND

Prognostic indicators of the malignant potential of pancreatic neuroendocrine tumors (PNET) are limited. We assessed tumor shape and enhancement pattern on contrast-enhanced computed tomography as predictors of malignant potential.

METHODS

Sixty cases of PNET patients undergoing curative surgery from 2001 to 2014 were enrolled onto our retrospective study. Preoperative enhanced CTs were assessed, and criteria defined for regularly shaped and enhancing tumors (group 1), and irregularly shaped and/or enhancing tumors (group 2). The relation of tumor shape and enhancement pattern to outcome was assessed.

RESULTS

Interobserver agreement was substantial (kappa = 0.74). Group 2 (n = 24) was significantly correlated with synchronous liver metastasis (23 vs. 0 %), lymph node metastasis (36 vs. 3 %), pathologic capsular invasion (68 vs. 8 %), larger tumor size (30 vs. 12 mm), tumor, node, metastasis classification system (TNM) stage III/IV disease (46 vs. 3 %), and histologic grade 2/3 (41 vs. 0 %). Multivariate analysis revealed that tumor grade 2/3 and group 2 criteria correlated with tumor relapse (hazard ratio 6.5 and 13.6, P = 0.0071 and 0.039, respectively), and that only group 2 criteria were independently correlated with poor overall survival (hazard ratio 5.56e + 9, P = 0.0041).

CONCLUSIONS

Irregular tumor shape/enhancement on preoperative computed tomography is a negative prognostic factor after curative surgery for PNET.

18F-FDG PET/CT Volumetric Parameters are Associated with Tumor Grade and Metastasis in Pancreatic Neuroendocrine Tumors in von Hippel-Lindau Disease

BACKGROUND

Approximately 8-17 % of patients with von Hippel-Lindau (VHL) syndrome develop pancreatic neuroendocrine tumors (PNETs), with 11-20 % developing metastases. Tumor grade is predictive of prognosis.

OBJECTIVE

The aim of this study was to determine if preoperative metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were associated with metastatic disease and tumor grade.

METHODS

Sixty-two patients with VHL-associated PNETs prospectively underwent ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT). MTV, TLG, and maximum standardized uptake value (SUV_max) were measured using a semi-automatic method. Surgically resected PNETs were classified according to 2010 World Health Organization tumor grade classification. MTV, TLG, and SUV_max were analyzed by metastatic disease and tumor grade using the Mann-Whitney test.

RESULTS

A total of 88 PNETs were identified by CT and ¹⁸F-FDG PET/CT, 10 of which were non-FDG-avid. Histologic grading was available for 20 surgical patients. Patients with metastatic PNETs had a higher TLG (median 25.9 vs. 7.7 mean SUV [SUV_mean]*mL; p = 0.0092) compared with patients without metastasis, while patients with grade 2 PNETs had a higher MTV (median 6.9 vs. 2.6 mL; p = 0.034) and TLG (median 41.2 vs. 13.1 SUV_mean*mL; p = 0.0035) compared with patients with grade 1 PNETs. No difference in tumor size or SUV_max was observed between the groups.

CONCLUSIONS

Patients with metastatic PNETs have a higher TLG compared with patients without metastasis. Grade 2 PNETs have a higher MTV and TLG compared with grade 1 PNETs. Tumor size and SUV_max were not associated with grade. Volumetric parameters on ¹⁸F-FDG PET/CT may be useful in detecting higher grade PNETs with a higher malignant potential that may need surgical intervention.