Therapeutic monitoring of gastroenteropancreatic neuroendocrine tumors: the challenges ahead

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.

Parametric net influx rate imaging of 68Ga-DOTATATE in patients with neuroendocrine tumors: assessment of lesion detectability

OBJECTIVES

There has been developed a clinical dynamic total-body 68Ga-DOTATATE PET/CT imaging protocol that allows quantitative imaging of net influx rate (Ki). Using qualitative and quantitative analyses of clinical studies, this retrospective study aims to assess whether parametric Ki images improve lesion detectability.

METHODS

Using a 194-cm axial field-of-view PET/CT scanner, 52 patients with neuroendocrine tumors underwent a 60-min dynamic total-body 68Ga-DOTATATE scan. Parametric Ki images and static standardized uptake value (SUV) images were generated. In addition to visual inspection of both sets of images, a quantitative analysis of 249 individual lesions was conducted using the target-to-background (TBR) metric.

RESULTS

There were 52 patients who underwent dynamic total-body 68Ga-DOTATATE PET/CT scans. A total of 249 lesions were evaluated, of which 66 lesions were biopsy-proven and 183 lesions were unproven. Ki images produced two fewer false positives than the SUV images. Overall, our results from 66 proven NET lesions suggested similar sensitivity (98.5%) but improved accuracy (from 95.6 to 97.1%) and potentially enhanced specificity with Ki over SUV imaging. Besides, there was no difference in the number of pathological lesions identified visually in both images. However, Ki TBR was significantly higher than SUV TBR quantitatively (P < 0.001).

CONCLUSIONS

Patlak Ki imaging provides nuclear physicians with a PET image with higher tumor contrast which may enhance confidence in diagnosis with possibly reduced false positive results, albeit an equivalent detectability, compared to static SUV image.

Tuberous sclerosis complex mutations in patients with pancreatic neuroendocrine tumors. Observations on phenotypic and treatment-related associations

Pancreatic neuroendocrine tumors (PanNETs) in familial tuberous sclerosis (TSC1 and TSC2 mutations) have been known and studied. However, little is known about PanNET patients harboring the very rare (less than 2%) sporadic TSC mutations. Some renal tumors have been shown to harbor sporadic TSC mutations, with a distinctive morphological correlate. We hereby describe this rather unusual molecular alteration in well-differentiated pancreatic neuroendocrine tumors (WD PanNETs) with a focus on their morphology and treatment outcomes. Six cases of WD PanNETs harboring sporadic TSC mutations were identified retrospectively. H&E slides and corresponding immunostains were reviewed for all cases. Clinical, molecular, and radiological information was obtained using the electronic medical records. Cohort consisted of 4 males and 2 females. Median age at diagnosis was 50 years (range 33-74 years). Origin of neoplasm was the pancreas and, in all but one, patient had liver metastasis by the time of presentation. Six out of six cases demonstrated a unique tumor morphology, with ample eosinophilic cytoplasm. Tumors were arranged in sheets and nests; prominent cystic change was noted in one case. Two cases were additionally biopsied post-treatment with capecitabine and temozolomide, and showed even more abundant oncocytic cytoplasm, eccentric nuclei, and a prominent cherry red nucleolus, and were arranged in a cluster of 3-4 cells, separated by stromal cells. Every patient had a different TSC2 variant with no cases of TSC1 mutations. Other common variants included MEN1 (4/6), DAXX (2/6), and TP53 (2/6). Per the WH0 2019 classification, tumors were graded as NET-G3 (n = 3) and NET-G2 (n = 3). Ki-67 s ranged from 7.2 to 60. All cases had retained MMR protein expression. The majority of patients (4/6) have expired. Although they received multiple treatments, a consistent pattern observed in patients was marked radiologic response to chemotherapy with capecitabine and temozolomide (offered in 5/6 patients) with duration of responses reaching 11 months in the majority of cases, with one patient showing near complete pathologic response of localized disease. TSC2 mutations may confer distinctive appearance in WD PanNETs, reminiscent of their effects in renal tumors. Although not entirely specific, this distinct morphological pattern with abundant eosinophilic cytoplasm in WD PanNETs could be reflective of an associated TSC mutation, with suggestions of significant therapeutic response to a specific cytotoxic chemotherapy.

Dynamic Total-Body PET/CT Imaging Reveals Kinetic Distribution of 68Ga-DOTATATE in Normal Organs

Objective

To investigate the biodistribution and kinetic constants of ⁶⁸Ga-DOTATATE in normal organs through dynamic total-body positron emission tomography/computed tomography (PET/CT).

Methods

Seven patients who experienced endoscopic resection of gastric neuroendocrine tumor were enrolled. Dynamic total-body PET/CT scans over 60 min were performed. Time-activity curves were obtained by drawing regions of interest in normal organs. Rate constants, including K ₁, k ₂, k ₃, and vB, were computed using a two-tissue compartment model. Factor analysis was used to compare the rate constants among subjects and regions. Hierarchical cluster analysis was performed to identify organs with similar kinetic characteristics.

Results

The highest uptake of ⁶⁸Ga-DOTATATE was observed in the spleen followed by kidneys, adrenals, liver, pituitary gland, pancreas head, prostate, pancreas body, and thyroid, parotid, and submandibular glands. Low background level of ⁶⁸Ga-DOTATATE uptake was observed in the nasal mucosa, bone, blood pool, and cerebrum. In addition, the uptake in the pancreas head was noted to be higher than the pancreas body (P < 0.001) on the basis of each time point of dynamic PET. There were differences of rate constants among different organs. The mean K ₁ ranged from 0.0507 min^-1 in the left nasal mucosa to 1.21 min^-1 in the left kidney, and mean k ₂ ranged from 0.0174 min^-1 in the spleen to 4.4487 min^-1 in the left cerebrum. The mean k ₃ ranged from 0.0563 min^-1 in the right cerebrum to 4.6309 min^-1 in the left adrenal, and mean vB ranged from 0.0001 in the left cerebrum to 0.2489 in the right adrenal. However, none of the rate constants was significantly different among subjects or among different sites within a single organ. Three groups of organs with similar kinetic characteristics were identified: (1) cerebrum; (2) pituitary gland, liver, adrenal, and prostate; and (3) nasal mucosa, parotid and submandibular glands, thyroid, spleen, pancreas, kidney, and bone.

Conclusion

Uptake and clearance of ⁶⁸Ga-DOTATATE, in terms of kinetic constants, were different in different organs. The kinetic parameters of ⁶⁸Ga-DOTATATE in different organs provide a reference for future dynamic PET imaging.

Molecular imaging phenotyping for selecting and monitoring radioligand therapy of neuroendocrine neoplasms

Neuroendocrine neoplasia (NEN) is an umbrella term that includes a widely heterogeneous disease group including well-differentiated neuroendocrine tumours (NETs), and aggressive neuroendocrine carcinomas (NECs). The site of origin of the NENs is linked to the intrinsic tumour biology and is predictive of the disease course. It is understood that NENs demonstrate significant biologic heterogeneity which ultimately translates to widely varying clinical presentations, disease course and prognosis. Thus, significant emphasis is laid on the pre-therapy evaluation of markers that can help predict tumour behavior and dynamically monitors the response during and after treatment. Most well-differentiated NENs express somatostatin receptors (SSTRs) which make them appropriate for peptide receptor radionuclide therapy (PRRT). However, the treatment outcomes of PRRT depend heavily on the adequacy of patient selection by molecular imaging phenotyping not only utilizing pre-treatment SSTR PET but ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) PET to provide insights into the intra- or inter-tumoural heterogeneity of the metastatic disease. Molecular imaging phenotyping may go beyond patient selection and provide useful information during and post-treatment for monitoring of temporal heterogeneity of the disease and dynamically risk-stratify patients. In addition, advances in the understanding of genomic-phenotypic classifications of pheochromocytomas and paragangliomas led to an archetypical example in precision medicine by utilizing molecular imaging phenotyping to guide radioligand therapy. Novel non-SSTR based peptide receptors have also been explored diagnostically and therapeutically to overcome the tumour heterogeneity. In this paper, we review the current molecular imaging modalities that are being utilized for the characterization of the NENs with special emphasis on their role in patient selection for radioligand therapy.

Are recist criteria adequate in assessing the response to therapy in metastatic NEN?

Response to therapy criteria, known as RECIST (Response Evaluation Criteria in Solid Tumours), are widely used to evaluate neuroendocrine tumours (NET) metastatic to the liver, under treatment. RECIST criteria does not take in account many various distinct features such as tumour growth, secretory capacity and anatomical localisation with wide variation in clinical and biological presentation of different NETs. Key features of RECIST includes definitions of the minimal size of measurable lesions, instructions on how many lesions to measure and follow, and the use of unidimensional, rather than bidimensional, measures for overall evaluation of tumour burden. These measures are currently done with computed tomography (CT) or Magnetic Resonance Imaging (MRI). RECIST criteria are accurate in assessing tumour progression but sometimes inaccurate in assessing tumour response after locoregional therapy or under molecular targeted therapy, tumour vessels being part of the target of such treatments. There is poor correlation between a so called tumour necrosis and conventional methods of response assessment, which poses questions of how best to quantify efficacy of these targeted therapies. Variations in tumour density with computed tomography (CT) could theoretically be associated with tumour necrosis. This hypothesis has been studied proposing alternative CT criteria of response evaluation in metastatic digestive NET treated with targeted therapy. If preliminary results upon the poor relationship between density measured with CT (derived from CHOI criteria) evolution curves at CT and PFS are confirmed by further studies, showing that the correlation between density changing and response to non-targeted treatment is weak, the use of contrast injection, will probably be not mandatory to enable appropriate evaluation.

Tumor growth rate in pancreatic neuroendocrine tumor patients undergoing PRRT with 177Lu-DOTATATE

BACKGROUND

Monitoring of pancreatic neuroendocrine tumors (PanNET) undergoing peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE depends on changes in tumor size, which often occur late. Tumor growth rate (TGR) allows for quantitative assessment of the tumor kinetics expressed as %/month. We explored how TGR changes before and during/after PRRT and evaluated TGR as a biomarker for progression-free survival (PFS).

METHODS

In PanNET patients undergoing PRRT with 177Lu-DOTATATE from 2006 to 2018, contrast-enhanced CT or MRI was performed before and during the therapy. Patients with at least one hypervascular liver metastasis were included. TGR was calculated for the period preceding treatment and for two intervals during/after PRRT. Cox regression was used for the survival analysis.

RESULTS

Sixty-seven patients (43 men, 24 women), median age 60 years (range 29-77), median Ki-67 10% (range 1-30) were included. TGR before baseline (n = 57) (TGR0) was mean (s.d.) 6.0%/month (s.d. = 8.7). TGR at 4.5 months (n = 56) (TGR4) from baseline was -3.4 (s.d. = 4.2) %/month. TGR at 9.9 months (n = 57) (TGR10) from baseline was -3.0 (s.d. = 2.9) %/month. TGR4 and TGR10 were lower than TGR0 (TGR4 vs TGR0, P < 0.001 and TGR10 vs TGR0, P < 0.001). In the survival analysis, patients with TGR10 ≥ 0.5%/month (vs <0.5%/month) had shorter PFS (median = 16.0 months vs 31.5 months, hazard ratio 2.82; 95% CI 1.05-7.57, P = 0.040).

DISCUSSION

TGR in PanNET patients decreases considerably during PRRT with 177Lu-DOTATATE. TGR may be useful as a biomarker to identify patients with the shortest PFS.

Tumor Growth Rate to Predict the Outcome of Patients with Neuroendocrine Tumors: Performance and Sources of Variability

INTRODUCTION

Tumor growth rate (TGR), percentage of change in tumor volume/month, has been previously identified as an early radiological biomarker for treatment monitoring in neuroendocrine tumor (NET) patients. We assessed the performance and reproducibility of TGR at 3 months (TGR3m) as a predictor factor of progression-free survival (PFS), including the impact of imaging method and reader variability.

METHODS

Baseline and 3-month (±1 month) CT/MRI images from patients with advanced, grade 1-2 NETs were retrospectively reviewed by 2 readers. Influence of number of targets, tumor burden, and location of lesion on the performance of TGR3m to predict PFS was assessed by uni/multivariable Cox regression analysis. Agreement between readers was assessed by Lin's concordance coefficient (LCC) and kappa coefficient (KC).

RESULTS

A total of 790 lesions were measured in 222 patients. Median PFS was 22.9 months. On univariable analysis, number of lesions (</≥4), tumor burden, and presence of liver metastases were significantly correlated with PFS. On multivariate analysis, ≥4 lesions (HR: 1.89 [95% CI: 1.01-3.57]), TGR3m ≥0.8%/month (HR: 4.01 [95% CI: 2.31-6.97]), and watch and wait correlated with shorter PFS. No correlation was found between TGR3m and number of lesions (rho: -0.2; p value: 0.1930). No difference in mean TGR3m across organs was shown (p value: 0.6). Concordance between readers was acceptable (LCC: 0.52 [95% CI: 0.38-0.65]; KC: 0.57, agreement: 81.55%). TGR3m remained a significant prognostic factor when data from the second reader were employed (HR: 4.35 [95% CI: 2.44-7.79]; p value <0.001) regardless his expertise (HR: 1.21 [95% CI: 0.70-2.09]; p value: 0.493).

DISCUSSION/CONCLUSION

TGR3m is a robust and early radiological biomarker able to predict PFS. It may be used to identify patients with advanced NETs who require closer radiological follow-up.

The Challenge of Evaluating Response to Peptide Receptor Radionuclide Therapy in Gastroenteropancreatic Neuroendocrine Tumors: The Present and the Future

The NETTER-1 study has proven peptide receptor radionuclide therapy (PRRT) to be one of the most effective therapeutic options for metastatic neuroendocrine tumors (NETs), improving progression-free survival and overall survival. However, PRRT response assessment is challenging and no consensus on methods and timing has yet been reached among experts in the field. This issue is owed to the suboptimal sensitivity and specificity of clinical biomarkers, limitations of morphological response criteria in slowly growing tumors and necrotic changes after therapy, a lack of standardized parameters and timing of functional imaging and the heterogeneity of PRRT protocols in the literature. The aim of this article is to review the most relevant current approaches for PRRT efficacy prediction and response assessment criteria in order to provide an overview of suitable tools for safe and efficacious PRRT.

Early response assessment and prediction of overall survival after peptide receptor radionuclide therapy

Background

Response after peptide receptor radionuclide therapy (PRRT) can be evaluated using anatomical imaging (CT/MRI), somatostatin receptor imaging ([⁶⁸Ga]Ga-DOTA-TATE PET/CT), and serum Chromogranin-A (CgA). The aim of this retrospective study is to assess the role of these response evaluation methods and their predictive value for overall survival (OS).

Methods

Imaging and CgA levels were acquired prior to start of PRRT, and 3 and 9 months after completion. Tumour size was measured on anatomical imaging and response was categorized according to RECIST 1.1 and Choi criteria. [⁶⁸Ga]Ga-DOTA-TATE uptake was quantified in both target lesions depicted on anatomical imaging and separately identified PET target lesions, which were either followed over time or newly identified on each scan with PERCIST-based criteria. Response evaluation methods were compared with Cox regression analyses and Log Rank tests for association with OS.

Results

A total of 44 patients were included, with median follow-up of 31 months (IQR 26–36 months) and median OS of 39 months (IQR 32mo-not reached)d. Progressive disease after 9 months (according to RECIST 1.1) was significantly associated with worse OS compared to stable disease [HR 9.04 (95% CI 2.10–38.85)], however not compared to patients with partial response. According to Choi criteria, progressive disease was also significantly associated with worse OS compared to stable disease [HR 6.10 (95% CI 1.38–27.05)] and compared to patients with partial response [HR 22.66 (95% CI 2.33–219.99)]. In some patients, new lesions were detected earlier with [⁶⁸Ga]Ga-DOTA-TATE PET/CT than with anatomical imaging. After 3 months, new lesions on [⁶⁸Ga]Ga-DOTA-TATE PET/CT which were not visible on anatomical imaging, were detected in 4/41 (10%) patients and in another 3/27 (11%) patients after 9 months. However, no associations between change in uptake on ⁶⁸Ga-DOTA-TATE PET/CT or serum CgA measurements and OS was observed.

Conclusions

Progression on anatomical imaging performed 9 months after PRRT is associated with worse OS compared to stable disease or partial response. Although new lesions were detected earlier with [⁶⁸Ga]Ga-DOTA-TATE PET/CT than with anatomical imaging, [⁶⁸Ga]Ga-DOTA-TATE uptake, and serum CgA after PRRT were not predictive for OS in this cohort with limited number of patients and follow-up time.

Tumor Contrast-Enhancement for Monitoring of PRRT 177Lu-DOTATATE in Pancreatic Neuroendocrine Tumor Patients

Background: Therapy monitoring of cancer treatment by contrast-enhanced CT (CECT), applying response evaluation criteria in solid tumors criteria version 1. 1 (RECIST 1.1) is less suitable for neuroendocrine tumors (NETs) which, when responding, tend to show stabilization rather than shrinkage. New methods are needed to further classify patients in order to identify non-responders at an early stage and avoid unnecessary adverse effects and costs. Changes in arterial tumor attenuation and contrast-enhancement could be used to identify the effect of therapy, perhaps even in early stages of treatment.

Methods: Patients with metastatic pancreatic NETs (PNETs) receiving peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE underwent CECT at baseline, mid-treatment (PRRT cycles 3–5) and at follow-up, 3 months after the last PRRT cycle. At baseline CECT, the liver metastasis with the highest arterial attenuation was identified in each patient. The fold changes in arterial tumor attenuation (Hounsfield Units, HU), contrast-enhancement (HU), and transversal tumor area (cm²) between CECT at baseline, mid-treatment and follow-up were calculated. Correlation of the tumor metrics to outcome parameters such as progression-free survival (PFS) and time to best response was performed.

Results: Fifty-two patients were included (27 men, 25 women), median age 60 years (range 29–80), median Ki-67 8% (range 1–30). Six patients had grade 1 PNETs, forty had grade 2 and four had grade 3 tumors. As an internal control, it was first tested and established that the tumor contrast-enhancement was not merely related to that of the abdominal aorta. The mean ± SD arterial attenuation of the liver metastases was similar at baseline, 217 ± 62 HU and at mid-treatment, 238 ± 80 HU and then decreased to 198 ± 62 HU at follow-up, compared to baseline (p = 0.024, n = 52) and mid-treatment (p = 0.0004, n = 43). The transversal tumor area decreased 25% between baseline and follow-up (p = 0.013, n = 52). Tumor contrast-enhancement increased slightly from baseline to mid-treatment and these fold changes correlated with PFS (R² = 0.33, p = 0.0002, n = 37) and with time to best response (R² = 0.34, p < 0.0001, n = 37).

Conclusions: Early changes in contrast-enhancement and arterial attenuation in PNET liver metastases may for CECT monitoring of PRRT yield complementary information to evaluation by RECIST 1.1.

Tumor-to-Blood Ratio for Assessment of Somatostatin Receptor Density in Neuroendocrine Tumors Using 68Ga-DOTATOC and 68Ga-DOTATATE

PET/CT with ⁶⁸Ga-DOTA-somatostatin analogs has been tested for therapy monitoring in patients with neuroendocrine tumors (NETs). However, SUVs in tumors do not correlate with the net influx rate (K_i), as a representation of the somatostatin receptor expression. In this study, tumor-to-blood ratio (TBR) was evaluated as an alternative tool for semiquantitative assessment of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE tumor uptake and as a therapy monitoring tool for patients with NETs. Methods: Twenty-two NET patients underwent a 45-min dynamic PET/CT scan after injection of ⁶⁸Ga-DOTATOC or ⁶⁸Ga-DOTATATE. K_i was determined using the Patlak method, and TBR was calculated for the 40- to 45-min interval. Results: A linear relation was found between K_i and TBR, with a square of Pearson correlation of 0.98 and 0.93 for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. Conclusion: A high correlation was found between K_i and TBR. Hence, TBR reflects somatostatin receptor density more accurately than SUV and is suggested as the preferred metric for semiquantitative assessment of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE tumor uptake.

[68Ga]-Dota Peptide PET/CT in Neuroendocrine Tumors: Main Clinical Applications

Objective:

Neuroendocrine Neoplasms (NENs) are generally defined as rare and heterogeneous tumors. The gastrointestinal system is the most frequent site of NENs localization, however they can be found in other anatomical regions, such as pancreas, lungs, ovaries, thyroid, pituitary, and adrenal glands. Neuroendocrine neoplasms have significant clinical manifestations depending on the production of active peptide.

Methods:

Imaging modalities play a fundamental role in initial diagnosis as well as in staging and treatment monitoring of NENs, in particular they vastly enhance the understanding of the physiopathology and diagnosis of NENs through the use of somatostatin analogue tracers labeled with appropriate radioisotopes. Additionally, the use of somatostatin analogues provides the ability to in-vivo measure the expression of somatostatin receptors on NEN cells, a process that might have important therapeutic implications.

Results:

A large body of evidences showed improved accuracy of molecular imaging based on PET/CT radiotracer with SST analogues (e.g. [68Ga]-DOTA peptide) for the detection of NEN lesions in comparison to morphological imaging modalities. So far, the role of imaging technologies in assessing treatment response is still under debate.

Conclusion:

This review offers the systems of classification and grading of NENs and summarizes the more useful recommendations based on data recently published for the management of patients with NENs, with special focus on the role of imaging modalities based on SST targeting with PET / CT radiotracers.

Tumor growth rate as a metric of progression, response, and prognosis in pancreatic and intestinal neuroendocrine tumors

Background

Lanreotide depot/autogel antitumor activity in intestinal/pancreatic neuroendocrine tumors (NETs) was demonstrated in the phase-3 CLARINET study (NCT00353496), based on significantly prolonged progression-free survival (PFS) versus placebo.

Methods

During CLARINET, patients with metastatic intestinal/pancreatic NETs received lanreotide depot/autogel 120 mg or placebo every 4 weeks for 96 weeks. Imaging data (response evaluation criteria in solid tumors [RECIST] v1.0, centrally reviewed) were re-evaluated in this post hoc analysis of tumor growth rate (TGR) in NETs. TGR (%/month) was calculated from two imaging scans during relevant periods: pre-treatment (TGR₀); 12–24 weeks before randomization versus baseline; each treatment visit versus baseline (TGR_Tx-0); between consecutive treatment visits (TGR_Tx-Tx). To assess TGR as a measure of prognosis, PFS was compared for TGR₀ subgroups stratified by optimum TGR₀ cut-off; a multivariate analysis was conducted to identify prognostic factors for PFS.

Results

TGR₀ revealed tumors growing during pre-treatment (median [interquartile range] TGR₀: lanreotide 2.1%/month [0.2; 6.1]; placebo 2.7%/month [0.15; 6.8]), contrary to RECIST status. TGR was significantly reduced by 12 weeks with lanreotide versus placebo (difference in least-square mean TGR_0–12 of − 2.9 [− 5.1, − 0.8], p = 0.008), a difference that was maintained at most subsequent visits. TGR₀ > 4%/month had greater risk of progression/death than ≤4%/month (hazard ratio 4.1; [95% CI 2.5–6.5]; p < 0.001); multivariate analysis revealed lanreotide treatment, progression at baseline, TGR₀, hepatic tumor load, and primary tumor type were independently associated with PFS.

Conclusions

TGR provides valuable information on tumor activity and prognosis in patients with metastatic intestinal/pancreatic NETs, and identifies early lanreotide depot/autogel antitumor activity.

Trial registration

Retrospective registration, 18 July 2006; EudraCT: 2005–004904-35; ClinicalTrials.gov: NCT00353496.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-5257-x) contains supplementary material, which is available to authorized users.

The NETest: The Clinical Utility of Multigene Blood Analysis in the Diagnosis and Management of Neuroendocrine Tumors

The neuroendocrine neoplasms test (NETest) is a multianalyte liquid biopsy that measures neuroendocrine tumor gene expression in blood. This unique signature precisely defines the biological activity of an individual tumor in real time. The assay meets the 3 critical requirements of an optimal biomarker: diagnostic accuracy, prognostic value, and predictive therapeutic assessment. NETest performance metrics are sensitivity and specificity and in head-to-head comparison are 4-fold to 10-fold more accurate than chromogranin A. NETest accurately identifies completeness of surgery and response to somatostatin analogs. Clinical registry data demonstrate significant clinical utility in watch/wait programs.

Clinical and Prognostic Value of PET/CT Imaging with Combination of 68Ga-DOTATATE and 18F-FDG in Gastroenteropancreatic Neuroendocrine Neoplasms

Background

To evaluate the clinical and prognostic value of PET/CT with combination of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG in gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs).

Method

83 patients of GEP-NENs who underwent ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT were enrolled between June 2013 and December 2016. Well-differentiated (WD) NETs are divided into group A (Ki-67 < 10%) and group B (Ki-67 ≥ 10%), and poorly differentiated (PD) NECs are defined as group C. The relationship between PET/CT results and clinicopathological characteristics was retrospectively investigated.

Result

For groups A/B/C, the sensitivities of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG were 78.8%/83.3%/37.5% and 52.0%/72.2%/100.0%. A negative correlation between Ki-67 and SUV_max of ⁶⁸Ga-DOTATATE (R = −0.415; P ≤ 0.001) was observed, while a positive correlation was noted between Ki-67 and SUV_max of ¹⁸F-FDG (R = 0.683; P ≤ 0.001). 62.5% (5/8) of patients showed significantly more lesions in the bone if ⁶⁸Ga-DOTATATE was used, and 22.7% (5/22) of patients showed more lymph node metastases if ¹⁸F-FDG was used.

Conclusions

The sensitivity of dual tracers was correlated with cell differentiation, and a correlation between Ki-67 and both SUV_max of PET-CTs could be observed. ⁶⁸Ga-DOTATATE is suggested for WD-NET and ¹⁸F-FDG is probably suitable for patients with Ki-67 ≥ 10%.

Determination of an optimal response cut-off able to predict progression-free survival in patients with well-differentiated advanced pancreatic neuroendocrine tumours treated with sunitinib: an alternative to the current RECIST-defined response

Background:

Sunitinib prolongs progression-free survival (PFS) in patients with advanced pancreatic neuroendocrine tumours (pNET). Response Evaluation Criteria in Solid Tumors (RECIST)-defined partial responses (PR; classically defined as ⩾30% size decrease from baseline) are infrequent.

Methods:

Individual data of pNET patients from the phase II [NCT00056693] and pivotal phase III [NCT00428597] trials of sunitinib were analysed in this investigator-initiated, post hoc study. The primary objective was to determine the optimal RECIST (v.1.0) response cut-off value to identify patients who were progression-free at 11 months (median PFS in phase III trial); and the most informative time-point (highest area under the curve (AUC) by receiver operating characteristic (ROC) analysis and logistic regression) for prediction of benefit (PFS) from sunitinib.

Results:

Data for 237 patients (85 placebo; 152 sunitinib (n=66.50 mg ‘4-weeks on/2-weeks off’ schedule; n=86 ‘37.5 mg continuous daily dosing (CDD)’)) and 788 scans were analysed. The median PFS for sunitinib and placebo were 9.3 months (95% CI 7.6–12.2) and 5.4 months (95% CI 3.5–6.01), respectively (hazard ratio (HR) 0.43 (95% CI 0.29–0.62); P<0.001). A PR was seen in 19 patients (13%) on sunitinib; the median change in the sum of the lesions (vs baseline) was −12.8% (range −100 to +36.4). Month 7 was the most informative time-point (AUC 0.78 (95% CI 0.66–0.9); odds ratio 1.05 (95% CI 1.01–1.08), P=0.002). Reduction of 10% (vs baseline) achieved the highest sensitivity (50%) and specificity (82%), amongst cut-offs tested. A 10% reduction in marker lesions was associated with improved PFS in the whole sunitinib population (HR 0.55 (95 CI 0.3–0.9); P=0.04); mostly in patients on sunitinib CDD (HR 0.33 (95% CI 0.2–0.7); P=0.005). A 10% reduction in marker lesions (P=0.034) and sunitinib treatment (P=0.012) independently impacted on PFS (multivariable analysis).

Conclusions:

A 10% reduction within marker lesions identifies pNET patients benefiting from sunitinib treatment with implications for maintenance of dose intensity and future trial design.

The Diagnosis and Treatment of Bronchopulmonary Carcinoid

BACKGROUND

The spectrum of primary neuroendocrine tumors of the lungs ranges from typical carcinoid tumors, which are relatively benign, to highly aggressive small-cell carcinoma. In this review, we summarize the treatment of bronchopulmonary carcinoid, a disease with an incidence of 0.5 per 100,000 persons per year in Western countries.

METHOD

We selectively searched the PubMed database for scientific evidence on the treatment of bronchopulmonary carcinoid, considering only articles published up to February 2015. We also performed a survival analysis of 84 patients with this disease who underwent interdisciplinary treatment at the University of Freiburg Medical Center.

RESULTS

Carcinoid tumors account for less than 1% of all lung tumors. They manifest themselves clinically with cough (35%), hemoptysis (25%), and/or bronchial obstruction (40%), depending on their location, size, and pattern of growth. 30% of patients are asymptomatic, and less than 1% have hormone-associated symptoms. Typical and atypical carcinoid tumors are distinguished on a histological basis; the histologic differential diagnosis also includes large-cell neuroendocrine tumors and small-cell carcinoma of the lung. 80% of patients who undergo resection of typical carcinoid tumors survive at least 10 years. Atypical carcinoid tumors recur more commonly than typical ones. If the mediastinal lymph nodes are involved, adjuvant treatment should be considered.

CONCLUSION

Because of their rarity, the treatment of bronchopulmonary carcinoid tumors presents an interdisciplinary challenge. Surgical resection, the treatment of choice for local carcinoid tumors, generally leads to long-term survival. The existing registers should be made more comprehensive so that the treatment of this disease can be better in the future.

Parametric Net Influx Rate Images of 68Ga-DOTATOC and 68Ga-DOTATATE: Quantitative Accuracy and Improved Image Contrast

⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE are radiolabeled somatostatin analogs used for the diagnosis of somatostatin receptor-expressing neuroendocrine tumors (NETs), and SUV measurements are suggested for treatment monitoring. However, changes in net influx rate (K_i) may better reflect treatment effects than those of the SUV, and accordingly there is a need to compute parametric images showing K_i at the voxel level. The aim of this study was to evaluate parametric methods for computation of parametric K_i images by comparison to volume of interest (VOI)-based methods and to assess image contrast in terms of tumor-to-liver ratio. Methods: Ten patients with metastatic NETs underwent a 45-min dynamic PET examination followed by whole-body PET/CT at 1 h after injection of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE on consecutive days. Parametric K_i images were computed using a basis function method (BFM) implementation of the 2-tissue-irreversible-compartment model and the Patlak method using a descending aorta image-derived input function, and mean tumor K_i values were determined for 50% isocontour VOIs and compared with K_i values based on nonlinear regression (NLR) of the whole-VOI time-activity curve. A subsample of healthy liver was delineated in the whole-body and K_i images, and tumor-to-liver ratios were calculated to evaluate image contrast. Correlation (R²) and agreement between VOI-based and parametric K_i values were assessed using regression and Bland-Altman analysis. Results: The R² between NLR-based and parametric image-based (BFM) tumor K_i values was 0.98 (slope, 0.81) and 0.97 (slope, 0.88) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. For Patlak analysis, the R² between NLR-based and parametric-based (Patlak) tumor K_i was 0.95 (slope, 0.71) and 0.92 (slope, 0.74) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. There was no bias between NLR and parametric-based K_i values. Tumor-to-liver contrast was 1.6 and 2.0 times higher in the parametric BFM K_i images and 2.3 and 3.0 times in the Patlak images than in the whole-body images for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. Conclusion: A high R² and agreement between NLR- and parametric-based K_i values was found, showing that K_i images are quantitatively accurate. In addition, tumor-to-liver contrast was superior in the parametric K_i images compared with whole-body images for both ⁶⁸Ga-DOTATOC and ⁶⁸Ga DOTATATE.

Imaging approaches to assess the therapeutic response of gastroenteropancreatic neuroendocrine tumors (GEP-NETs): current perspectives and future trends of an exciting field in development

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are a family of neoplasms with a complex spectrum of clinical behavior. Although generally more indolent than carcinomas, once they progress beyond surgical resectability, they are essentially incurable. Systemic treatment options have substantially expanded in recent years for the management of advanced disease. Imaging plays a major role in new drug development, as it is the main tool used to objectively evaluate response to novel agents. However, current standard response criteria have proven suboptimal for the assessment of the antiproliferative effect of many targeted agents, particularly in the context of slow-growing tumors such as well-differentiated NETs. The aims of this article are to discuss the advantages and limitations of conventional radiological techniques and standard response assessment criteria and to review novel imaging modalities in development as well as alternative cancer- and therapy-specific criteria to assess drug efficacy in the field of GEP-NETs.

A Delphic consensus assessment: imaging and biomarkers in gastroenteropancreatic neuroendocrine tumor disease management

The complexity of the clinical management of neuroendocrine neoplasia (NEN) is exacerbated by limitations in imaging modalities and a paucity of clinically useful biomarkers. Limitations in currently available imaging modalities reflect difficulties in measuring an intrinsically indolent disease, resolution inadequacies and inter-/intra-facility device variability and that RECIST (Response Evaluation Criteria in Solid Tumors) criteria are not optimal for NEN. Limitations of currently used biomarkers are that they are secretory biomarkers (chromogranin A, serotonin, neuron-specific enolase and pancreastatin); monoanalyte measurements; and lack sensitivity, specificity and predictive capacity. None of them meet the NIH metrics for clinical usage. A multinational, multidisciplinary Delphi consensus meeting of NEN experts (n = 33) assessed current imaging strategies and biomarkers in NEN management. Consensus (>75%) was achieved for 78% of the 142 questions. The panel concluded that morphological imaging has a diagnostic value. However, both imaging and current single-analyte biomarkers exhibit substantial limitations in measuring the disease status and predicting the therapeutic efficacy. RECIST remains suboptimal as a metric. A critical unmet need is the development of a clinico-biological tool to provide enhanced information regarding precise disease status and treatment response. The group considered that circulating RNA was better than current general NEN biomarkers and preliminary clinical data were considered promising. It was resolved that circulating multianalyte mRNA (NETest) had clinical utility in both diagnosis and monitoring disease status and therapeutic efficacy. Overall, it was concluded that a combination of tumor spatial and functional imaging with circulating transcripts (mRNA) would represent the future strategy for real-time monitoring of disease progress and therapeutic efficacy.

Circulating Transcript Analysis (NETest) in GEP-NETs Treated With Somatostatin Analogs Defines Therapy

CONTEXT

Early and precise delineation of therapeutic responses are key issues in neuroendocrine neoplasm/tumor management. Imaging is currently used but exhibits limitations in sensitivity and specificity. The utility of biomarkers is unclear. objective, setting, and design: This prospective cohort study (11 mo) sought to determine whether measurements of circulating neuroendocrine tumor transcripts (NETest) predict responses to somatostatin analogs (SSAs).

PATIENTS

The test set consisted of 35 SSA-treated gastroenteropancreatic-NETs (RECISTevaluated). The prospective set consisted of 28 SSA-treated Grade 1-Grade 2 GEP-NETs.

INTERVENTION(S)

Whole blood for transcript analysis (NETest) and plasma for Chromogranin A (CgA) (baseline), were collected every 4 weeks (prior to SSA injection). Morphologic (multidetector computed tomography/MRI) and functional imaging ((99m)Tc-[HYNIC, Tyr(3)]-Octreotide) was undertaken at entry and 6-month intervals until progression (RECIST 1.0).

MAIN OUTCOME MEASURE(S)

Treatment response.

RESULTS

Test set: NETest (≥80%; scale, 0-100%) differentiated stable (SD) and progressive (PD) disease (P < .0001). Prospective set: 28 patients (26/28 SD) undergoing standard SSA. Grading: 12 G1, 16 G2. SSA Response: progression-free survival: 315 days: 14 (50%) SD, 14 (50%) PD. NETest: Twenty had elevated (≥80%) values; 14 developed PD; six, SD. CgA: Twelve of 28 exhibited elevated baseline values and/or subsequent >25% increase; eight developed PD; four, SD. NETest (P = .002) and grade (P = .054) were the only factors associated with treatment response. Multiple regression analysis established that the NETest could predict disease progression (P = .0002). NETest changes occurred significantly earlier (146 d prior to progression vs 56 d CgA; P < .0001; χ(2) = 19) and in more patients (100 vs 57%; P < .02).

CONCLUSIONS

NETest values (80-100%) were more accurate and occurred at a significantly earlier time point than CgA and predicted SSA treatment response.

Decoding the Molecular and Mutational Ambiguities of Gastroenteropancreatic Neuroendocrine Neoplasm Pathobiology

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN), considered a heterogeneous neoplasia, exhibit ill-defined pathobiology and protean symptomatology and are ubiquitous in location. They are difficult to diagnose, challenging to manage, and outcome depends on cell type, secretory product, histopathologic grading, and organ of origin. A morphologic and molecular genomic review of these lesions highlights tumor characteristics that can be used clinically, such as somatostatin-receptor expression, and confirms features that set them outside the standard neoplasia paradigm. Their unique pathobiology is useful for developing diagnostics using somatostatin-receptor targeted imaging or uptake of radiolabeled amino acids specific to secretory products or metabolism. Therapy has evolved via targeting of protein kinase B signaling or somatostatin receptors with drugs or isotopes (peptide-receptor radiotherapy). With DNA sequencing, rarely identified activating mutations confirm that tumor suppressor genes are relevant. Genomic approaches focusing on cancer-associated genes and signaling pathways likely will remain uninformative. Their uniquely dissimilar molecular profiles mean individual tumors are unlikely to be easily or uniformly targeted by therapeutics currently linked to standard cancer genetic paradigms. The prevalence of menin mutations in pancreatic NEN and P27^KIP1 mutations in small intestinal NEN represents initial steps to identifying a regulatory commonality in GEP-NEN. Transcriptional profiling and network-based analyses may define the cellular toolkit. Multianalyte diagnostic tools facilitate more accurate molecular pathologic delineations of NEN for assessing prognosis and identifying strategies for individualized patient treatment. GEP-NEN remain unique, poorly understood entities, and insight into their pathobiology and molecular mechanisms of growth and metastasis will help identify the diagnostic and therapeutic weaknesses of this neoplasia.

The status of neuroendocrine tumor imaging: from darkness to light?

Diagnostic imaging plays a pivotal role in the diagnosis, staging, treatment selection and follow-up for neuroendocrine tumors. The available diagnostic strategies are morphologic imaging, including computed tomography, magnetic resonance imaging (MRI) and ultrasound techniques, and molecular imaging, including scintigraphy with (111)In-pentetreotide and positron emission tomography with (68)Ga-DOTA-peptides, (18)F-DOPA and (11)C-5-HTP. A combination of anatomic and functional techniques is routinely performed to optimize sensitivity and specificity. The introduction of diffusion-weighted MRI and dynamic contrast-enhanced techniques represents a promising advance in radiologic imaging, whereas new receptor-binding peptides, including somatostatin agonists and antagonists, represent the recent most favorable innovation in molecular imaging. Future development includes the short-term validation of these techniques, but in extension also a more comprehensive multilevel integration of biologic information pertaining to a specific tumor and patient, possibly encompassing genomic considerations, currently evolving as a new entity denoted 'precision medicine'. The ideal is a diagnostic sequence that captures the global status of an individual's tumor and encompasses a multidimensional characterization of tumor location, metabolic performance and target identification. To date, advances in imagery have focused on increasing resolution, discrimination and functional characterization. In the future, the fusion of imagery with the parallel analysis of biological and genomic information has the potential to considerably amplify diagnosis.

Can complementary 68Ga-DOTATATE and 18F-FDG PET/CT establish the missing link between histopathology and therapeutic approach in gastroenteropancreatic neuroendocrine tumors?

Gastroenteropancreatic neuroendocrine tumors (GEPNETs) are indolent neoplasms presenting unpredictable and unusual biologic behavior that causes many clinical challenges. Tumor size, existence of metastasis, and histopathologic classification remain incapable in terms of treatment decision and prognosis estimation. This study aimed to compare (68)Ga-DOTATATE and (18)F-FDG PET/CT in GEPNETs and to investigate the relation between the complementary PET/CT results and histopathologic findings in the management of therapy, particularly in intermediate-grade patients.

METHODS

The relation between complementary (68)Ga-DOTATATE and (18)F-FDG PET/CT results of 27 GEPNET patients (mean age, 56 y; age range, 33-79 y) and histopathologic findings was evaluated according to grade and localization using standardized maximum uptake values and Ki67 indices. Grade 2 (G2) patients were further evaluated in 2 groups as G2a (3%-9%) and G2b (10%-20%) according to Ki67 indices.

RESULTS

The sensitivity of (68)Ga-DOTATATE and (18)F-FDG PET/CT was 95% and 37%, respectively, and the positive predictive values were 93.8% and 36.2%, respectively. The sensitivity in detecting liver metastasis, lymph nodes, bone metastasis, and primary lesion was 95%, 95%, 90%, and 93% for (68)Ga-DOTATATE and 40%, 28%, 28%, and 75% for (18)F-FDG, respectively. Statistically significant differences were found between grades 1-2, 2a-2b, and 1-2b with respect to (68)Ga-DOTATATE PET/CT as well as between 1-2a and 1-2b with respect to (18)F-FDG PET/CT. However, no statistical differences were found between 1 and 2a (P > 0.05) for (68)Ga-DOTATATE and 2a and 2b (P = 0.484) for (18)F-FDG. The impact of the combined (18)F-FDG and (68)Ga-DOTATATE PET/CT on the therapeutic decision was 59%.

CONCLUSION

Combined (68)Ga-DOTATATE and (18)F-FDG PET/CT is helpful in the individual therapeutic approach of GEPNETs and can overcome the shortcomings of histopathologic grading especially in intermediate-grade GEPNETs.

Nordic guidelines 2014 for diagnosis and treatment of gastroenteropancreatic neuroendocrine neoplasms

BACKGROUND

The diagnostic work-up and treatment of patients with neuroendocrine neoplasms (NENs) has undergone major recent advances and new methods are currently introduced into the clinic. An update of the WHO classification has resulted in a new nomenclature dividing NENs into neuroendocrine tumours (NETs) including G1 (Ki67 index ≤ 2%) and G2 (Ki67 index 3-20%) tumours and neuroendocrine carcinomas (NECs) with Ki67 index > 20%, G3. Aim. These Nordic guidelines summarise the Nordic Neuroendocrine Tumour Group's current view on how to diagnose and treat NEN-patients and are meant to be useful in the daily practice for clinicians handling these patients.

Evaluating digestive neuroendocrine tumor progression and therapeutic responses in the era of targeted therapies: state of the art

Well-differentiated neuroendocrine tumors (NETs) are a group of heterogeneous rare tumors. They are often slow-growing and patients can have very long survival, even at the metastatic stage. The evaluation of tumor progression and therapeutic responses is currently based on Response Evaluation Criteria In Solid Tumors v1.1 (RECIST) criteria. As for other malignancies, RECIST criteria are being reexamined for NETs in the era of targeted therapies because tumor response to targeted therapies is rarely associated with shrinkage, as opposed to prolonged progression-free survival. Therefore, size-based criteria no longer seem to be suitable to the assessment of NET progression and therapeutic responses, especially considering targeted therapies. New imaging criteria, combining morphological and functional techniques, have proven relevant for other malignancies treated with targeted therapies. To date, such studies have rarely been conducted on NETs. Moreover, optimizing the management of NET patients also requires considering clinical, biological, and pathological aspects of tumor evolution. Our objectives herein were to comprehensively review current knowledge on the assessment of tumor progression and early prediction of therapeutic responses and to broaden the outlook on well-differentiated NETs, in the era of targeted therapies.

Neuroendocrine tumours: the role of imaging for diagnosis and therapy

In patients with neuroendocrine tumours (NETs), a combination of morphological imaging and nuclear medicine techniques is mandatory for primary tumour visualization, staging and evaluation of somatostatin receptor status. CT and MRI are well-suited for discerning small lesions that might escape detection by single photon emission tomography (SPECT) or PET, as well as for assessing the local invasiveness of the tumour or the response to therapy. Somatostatin receptor imaging, by (111)In-pentetreotide scintigraphy or PET with (68)Ga-labelled somatostatin analogues, frequently identifies additional lesions that are not visible on CT or MRI scans. Currently, somatostatin receptor scintigraphy with (111)In-pentetreotide is the more frequently available of the two techniques to determine somatostatin receptor expression and is needed to select patients for peptide receptor radionuclide therapy. In the future, because of its higher sensitivity, PET with (68)Ga-labelled somatostatin analogues is expected to replace somatostatin receptor scintigraphy. Whereas (18)F-FDG-PET is only used in high-grade neuroendocrine cancers, PET-CT with (18)F-dihydroxy-L-phenylalanine or (11)C-5-hydroxy-L-tryptophan is a useful problem-solving tool and could be considered for the evaluation of therapy response in the future. This article reviews the role of imaging for the diagnosis and management of intestinal and pancreatic NETs. Response evaluation and controversies in NET imaging will also be discussed.

(11)C-hydroxyephedrine positron emission tomography in the postoperative management of pheochromocytoma and paraganglioma

AIM

Accurate detection of recurrent disease and restaging are essential in the postoperative surveillance of many patients with pheochromocytomas (PHEOs) and paragangliomas (PGLs). In this study, the impact of positron emission tomography (PET) and PET/computed tomography (CT) with (11)C-hydroxyephedrine (HED) was evaluated for the postoperative surveillance and diagnosis of recurrent disease and for functional monitoring of locoregional and systemic therapy.

METHODS

One hundred and eleven HED-PET and PET/CT examinations performed in 48 patients after surgical intervention for PHEO/PGL were analyzed retrospectively. In a subgroup of 16 patients who underwent systemic and locoregional therapies, the tracer uptake in tumors was also measured as the functional volume (FV), maximum standardized uptake value (SUVmax), mean SUV (SUVmean) and as the total catecholamine transporter tumor volume (TCTTV) calculated as TCTTV = FV × SUVmean. The PET imaging results were correlated with CT/magnetic resonance imaging findings and biochemical and clinical follow-up data.

RESULTS

In the first postoperative examination, HED-PET was positive in 24/48 and negative in 24/48 patients with no false-positive results, yielding 92.3% sensitivity and 100% specificity. For the 16 patients, there was a significant correlation between FV and SUVmax and SUVmax and TCTTV. TCTTV correlated significantly with plasma and urinary catecholamines. In 11/16 patients, SUVmax and TCTTV increased/decreased in parallel but not in the remaining 5 patients.

CONCLUSION

HED-PET and PET/CT were found to be valuable in the postoperative follow-up in detecting recurrent and metastatic disease. In a subgroup of patients, functional monitoring of systemic and locoregional therapies was feasible by assessing the changes of the TCTTV, and therefore warrants further prospective evaluation.

Update on the management of gastroenteropancreatic neuroendocrine tumors with emphasis on the role of imaging

OBJECTIVE

The purposes of this article are to review the current management of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) based on the 2012 National Comprehensive Cancer Network guidelines and to describe the role of imaging in a multidisciplinary approach.

CONCLUSION

The management of GEP-NETs has become complex, requiring a multidisciplinary approach. The World Health Organization classification of GEP-NETs has been revised; the U.S. Food and Drug Administration has approved molecular targeted agents (sunitinib, everolimus) for the treatment of pancreatic NETs; and the National Comprehensive Cancer Network clinical practice guidelines have been updated.

Theranostics with Ga-68 somatostatin receptor PET/CT: monitoring response to peptide receptor radionuclide therapy

Peptide receptor radionuclide therapy involves selective targeting of neuroendocrine tumors through the somatostatin receptors, the aim being to increase radiation dose to the tumors and spare the normal tissue. The advantage of this internal radiation therapy is the ability to selectively target multiple metastases throughout the body. Early and accurate assessment of therapy response helps not only to identify the poor responders but also to personalize the treatment regimes with the aim of achieving maximum treatment benefit. This is the basis of theranostics.

Diffusion-weighted imaging with acquisition of three b-values for response evaluation of neuroendocrine liver metastases undergoing selective internal radiotherapy

OBJECTIVES

To evaluate diffusion-weighted MRI with acquisition of three b-values and calculation of fractioned ADCs for response evaluation of neuroendocrine liver metastases undergoing selective internal radiotherapy (SIRT).

METHODS

Ten consecutive patients with neuroendocrine liver metastases underwent MRI before and following SIRT. Diffusion-weighted imaging included acquisition of the b-values 0, 50 and 800 s/mm(2) and calculation of ADC(50,800), ADC(0,50) and ADC(0,800) maps. According to therapy response, lesions were categorised into group A [≥20% reduction of the longest diameter (LD) in comparison to baseline MRI] and group B (<20% reduction of the LD).

RESULTS

Twelve out of 31 metastases were categorised as group A and 19 out of 31 metastases were categorised as group B. Pretherapeutic values of ADC(0,800) and ADC(50,800) did not differ significantly between the two groups; however, ADC(0,50) was 32% lower in group A (P = 0.049). ADC(0,800) and ADC(50,800) increased significantly after therapy in both groups, however, group differences were not statistically significant. Conversely, the increase in ADC(0,50) was about a factor of 7 larger in group A than in group B (P = 0.023).

CONCLUSIONS

Our study showed that the ADC(0,50) is a promising biomarker for response assessment of neuroendocrine liver metastases following SIRT.

KEY POINTS

• Diffusion-weighted MRI offers new information about neuroendocrine hepatic metastases. • Evaluation of perfusion and diffusion components requires fractioned apparent diffusion coefficients (ADCs). • Perfusion effects represented by ADC (0.50) can be observed in neuroendocrine metastases. • Pretherapeutic ADC (0.50) was significantly lower in metastases with a response ≥20%. • Such biomarkers may help evaluate liver metastases in patients undergoing therapy.

Somatostatin receptor-based molecular imaging and therapy for neuroendocrine tumors

Neuroendocrine tumors (NETs) are tumors originated from neuroendocrine cells in the body. The localization and the detection of the extent of NETs are important for diagnosis and treatment, which should be individualized according to the tumor type, burden, and symptoms. Molecular imaging of NETs with high sensitivity and specificity is achieved by nuclear medicine method using single photon-emitting and positron-emitting radiopharmaceuticals. Somatostatin receptor imaging (SRI) using SPECT or PET as a whole-body imaging technique has become a crucial part of the management of NETs. The radiotherapy with somatostatin analogues labeled with therapeutic beta emitters, such as lutetium-177 or yttrium-90, has been proved to be an option of therapy for patients with unresectable and metastasized NETs. Molecular imaging can deliver an important message to improve the outcome for patients with NETs by earlier diagnosis, better choice of the therapeutic method, and evaluation of the therapeutic response.

Quantification in (68)Ga-DOTA(0)-Phe(1)-Tyr(3)-octreotide positron emission tomography/computed tomography: can we be impartial about partial volume effects?

AIM

In combined positron emission tomography/computed tomography (PET/CT) of neuroendocrine neoplasms using (68)Ga-DOTA(0)-Phe(1)-Tyr(3)-octreotide ((68)Ga-DOTATOC), partial volume effects (PVEs) may occur in smaller lesions. This study determined the lesional cutoff size for the occurrence of PVEs in a clinical setting.

METHODS

Retrospective assessment of 51 PET/CT examinations (16-slice PET/CT device) for malignant PET foci was carried out. In all foci, the maximal standardized uptake value (SUVmax) and maximal lesion diameter on axial CT was documented. Determined SUVmax and lesional sizes were correlated via LOESS regression. In the resulting curve, the cutoff point for SUVmax size dependency was determined visually and mathematically using 2 approximating straight lines.

RESULTS

In 45 patients, 313 of 413 PET foci found were malignant, measurable on CT and had a roughly spherical geometry (SUVmax: 2.5-103.3, mean ± SD 20.5 ± 15.18; CT diameter: 5-103 mm, mean ± SD 21.8 ± 13.1 mm). The cutoff lesional size for the occurrence of PVEs was 20.4 mm by the mathematical approach and 25 mm by visual assessment.

CONCLUSION

In (68)Ga-DOTATOC imaging, the clinical lesional size threshold is far larger than expected from systemic resolution only. Thus, tracer uptake quantification is only acceptable in sufficiently large lesions.

Radiological and nuclear medicine imaging of gastroenteropancreatic neuroendocrine tumours

Neuroendocrine tumours (NETs) comprise a heterogeneous group of neoplasms with very varying clinical expression. A functioning NET, for instance in the pancreas, may be very small and yet give rise to severe endocrine symptoms whereas a patient with a small bowel tumour may present with diffuse symptoms and disseminated disease with a palpable bulky liver. Imaging of NETs is therefore challenging and the imaging needs in the various patients are diverse. The basic modalities for NET imaging are computed tomography (CT) or magnetic resonance imaging (MRI) in combination with somatostatin receptor imaging (SMI) by scintigraphy with 111In-labelled octreotide (OctreoScan) or more recently by positron emission tomography (PET) with 68Ga-labelled somatostatin analogues. In this review these various morphological and functional imaging modalities and important methodological aspects are described. Imaging requirements for the various types of NETs are discussed and typical image findings are illustrated.