MIB-1 Index-Stratified Assessment of Dual-Tracer PET/CT with 68Ga-DOTATATE and 18F-FDG and Multimodality Anatomic Imaging in Metastatic Neuroendocrine Tumors of Unknown Primary in a PRRT Workup Setting

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.

Diagnostic Anatomic Imaging for Neuroendocrine Neoplasms: Maximizing Strengths and Mitigating Weaknesses

ABSTRACT

Neuroendocrine neoplasms are a heterogeneous group of gastrointestinal and lung tumors. Their diverse clinical manifestations, variable locations, and heterogeneity present notable diagnostic challenges. This article delves into the imaging modalities vital for their detection and characterization. Computed tomography is essential for initial assessment and staging. At the same time, magnetic resonance imaging (MRI) is particularly adept for liver, pancreatic, osseous, and rectal imaging, offering superior soft tissue contrast. The article also highlights the limitations of these imaging techniques, such as MRI's inability to effectively evaluate the cortical bone and the questioned cost-effectiveness of computed tomography and MRI for detecting specific gastric lesions. By emphasizing the strengths and weaknesses of these imaging techniques, the review offers insights into optimizing their utilization for improved diagnosis, staging, and therapeutic management of neuroendocrine neoplasms.

Surgery as a Principle and Technical Consideration for Primary Tumor Resection of Small Bowel Neuroendocrine Tumors

Small bowel neuroendocrine tumors (SB-NETs) are increasingly identified and have become the most frequent entity among small bowel tumors. An increasing incidence, a high prevalence, and a prolonged survival with optimal modern multidisciplinary management makes SB-NETs a unique set of tumors to consider for surgical oncologists. The major goals of surgical treatment in the setting of SB-NET include control of tumor volume, control of endocrine secretion, and prevention of locoregional complications. Key considerations include assessment of multifocality and resection of mesenteric nodal masses with the use of mesenteric-sparing approaches and acceptance of R1 margins if necessary to clear disease while avoiding short bowel syndrome. A description through eight steps for consideration is presented to allow for systematic surgical planning and execution of resection. Moreover, some controversies and evolving considerations to the surgical principles and technical procedures remain. The role of primary tumor resection in the presence of (unresectable) liver metastasis is still unclear. Reports of feasibility of minimally invasive surgery are emerging, with undetermined selection criteria for appropriateness or long-term outcomes. Resection of SB-NETs should be considered in all patients fit for surgery and should follow principles to achieve surgical oncological control that is appropriate for the stage and tumor burden, considering the age and comorbidity of the individual patient.

PPY-cell hyperplasia accompanying NENs: Immunohistochemical and nuclear medicine analysis

Pancreatic polypeptide cell hyperplasia (PPY-H) is a multiplication of the neuroendocrine cells producing pancreatic polypeptide (PPY). The development and role of PPY-H and its corresponding clinical and imaging findings still need to be fully elucidated. We present 12 cases of PPY-H accompanying pancreatic neuroendocrine neoplasias (NEN). PPY-H was analyzed with the help of immunohistochemistry and confocal microscopy; preoperative clinical data and imaging studies were evaluated retrospectively. We observed PPY-H emerging from pancreatic ducts, and in some cases, we observed simultaneous NKX6.1 positivity in ducts and PPY-H. Additional clinical-pathological correlations suggests that gastrointestinal symptoms (e.g., epigastric pain and cholestasis) could be more related to PPY-H than to NEN hormonal production. In particular cases, SSTR2 expression was strong in PPY-H and correlated with distinguishable accumulation of activity next to NEN on 99 mTc EDDA/Hynic-TOC SPECT/CT. In another case, 18F-FDG-PET/CT showed increased metabolic activity in the area of PPY-H surrounding NEN. Our data suggest that PPY-H originates in the lining of pancreatic ducts. Confirmation of SSTR2 in PPY-H, using immunohistochemistry, suggests the utility of 99 mTc EDDA/Hynic-TOC or 68Ga-DOTA radiotracers in clinical diagnostics; however, studies with larger cohort are needed.

Somatostatin Receptor Targeted PET-CT and Its Role in the Management and Theranostics of Gastroenteropancreatic Neuroendocrine Neoplasms

Somatostatin receptor (SSTR) agonist-based Positron Emission Tomography-Computed Tomography (PET-CT) imaging is nowadays the mainstay for the assessment and diagnostic imaging of neuroendocrine neoplasms (NEN), especially in well-differentiated neuroendocrine tumors (NET) (World Health Organization (WHO) grade I and II). Major clinical indications for SSTR imaging are primary staging and metastatic workup, especially (a) before surgery, (b) detection of unknown primary in metastatic NET, (c) patient selection for theranostics and appropriate therapy, especially peptide receptor radionuclide therapy (PRRT), while less major indications include treatment response evaluation on and disease prognostication. Dual tracer PET-CT imaging using SSTR targeted PET tracers, viz. [⁶⁸Ga]Ga-DOTA-Tyr3-Octreotate (DOTA-TATE) and [⁶⁸Ga]Ga-DOTA-NaI3-Octreotide (DOTA-NOC), and fluorodeoxyglucose (FDG), have recently gained widespread acceptance for better assessment of whole-body tumor biology compared to single-site histopathology, in terms of being non-invasive and the ability to assess inter- and intra-tumoral heterogeneity on a global scale. FDG uptake has been identified as independent adverse risk factor in various studies. Recently, somatostatin receptor antagonists have been shown to be more sensitive and specific in detecting the disease. The aim of this review article is to summarize the clinical importance of SSTR-based imaging in the clinical management of neuroendocrine and related tumors.

Lutathera® Orphans: State of the Art and Future Application of Radioligand Therapy with 177Lu-DOTATATE

Lutathera® is the first EMA- and FDA-approved radiopharmaceutical for radioligand therapy (RLT). Currently, on the legacy of the NETTER1 trial, only adult patients with progressive unresectable somatostatin receptor (SSTR) positive gastroenteropancreatic (GEP) neuroendocrine neoplasms (NET) can be treated with Lutathera®. Conversely, patients with SSTR-positive disease arising from outside the gastroenteric region do not currently have access to Lutathera® treatment despite several papers in the literature reporting the effectiveness and safety of RLT in these settings. Moreover, patients with well-differentiated G3 GEP-NET are also still “Lutathera orphans”, and retreatment with RLT in patients with disease relapse is currently not approved. The aim of this critical review is to summarize current literature evidence assessing the role of Lutathera® outside the approved indications. Moreover, ongoing clinical trials evaluating new possible applications of Lutathera® will be considered and discussed to provide an updated picture of future investigations.

Imaging Recommendations for Theranostic PET-CT in Oncology

We in this article have presented a review of the guideline recommendations on theranostic positron emission tomography-computed tomography (PET-CT) imaging which will be helpful to assist practitioners in providing appropriate patient care. Multiple guidelines by different societies and medical associations provide standards for diagnosis, imaging, and treatment of cancer patients. They have generated a number of recommendations related to 68Ga-DOTATATE and 68Ga-PSMA-11 PET-CT, which are the classical examples of theranostic PET-CT imaging in current practice.

Imaging Recommendations for Diagnosis, Staging, and Management of Carcinoma of Unknown Origin (Lymph Node, Pulmonary, Liver, Skeletal, and Brain) with Emphasis on the Current Position of PET-CT in Carcinoma of Unknown Origin (CUP)

Most of the established guidelines mention and recommend the use of FDG-PET/CT (fluorodeoxyglucose positron emission tomography/computed tomography) in carcinoma of unknown primary (CUP) especially in head–neck squamous cell carcinoma; as described in this article, this forms a powerful one-stop shop in diagnosing and staging modality and has multiple applications in difficult situations of CUPs. Although not used as a screening modality, FDG-PET/CT is recommended as the primary imaging modality in the evaluation of primary, staging, and response evaluation for CUP with histology known to demonstrate FDG avidity, especially patients presenting with lymph nodal disease. It should be remembered that many histological types do not concentrate on FDG and FDG also shows false-positive results in many other conditions like infection-inflammation; however, at the same time, it delivers high negative predictive values, an important consideration when employing FDG-PET/CT in the CUP scenario. SSTR-based PET/CT plays a pivotal role in primary diagnosis, staging, therapy planning, and response assessment in CUPs with neuroendocrine tumor or neuroendocrine neoplasm histology. The last two decades has witnessed great advancement in PET instrumentation and radiopharmaceuticals: particularly techniques like PET/magnetic resonance imaging and radiopharmaceuticals like FAPI (fibroblast-activation protein inhibitor)-based PET tracers. Hence, the role of PET/CT is expected to expand its reach in the coming years in line with accruing literature evidence, thereby upgrading its role and reliability in oncological practice strategies.

Discordance between Histopathological grading and Dual Tracer PET-CT findings (68Ga-DOTATATE and FDG) in metastatic Neuroendocrine Neoplasms and outcome of 177Lu-DOTATATE PRRT: does in-vivo molecular PET imaging perform better from 'prediction of tumour biology' viewpoint?

Background and Aim: Discordance between histopathological grading and dual tracer PET-CT (⁶⁸Ga-DOTATATE and FDG) findings in neuroendocrine tumours (NETs), though not typical, can be encountered in real-world scenario. The aim of this study was to assess patients with discordance between WHO 2017 grade predicted molecular PET-CT imaging and the actual dual tracer PET-CT findings (by exploring their histopathological, immunohistochemical and molecular imaging characteristics), with a view to identifying the prognostic determinants effecting outcome in a peptide receptor radionuclide therapy (PRRT) set-up. Methods: Thirty six patients of histopathologically proven inoperable, locally advanced/metastatic NETs, referred for PRRT were included in this study. The cohort was divided into two broad population groups: (a) those with discordance (between WHO 2017 grade predicted molecular imaging and the dual tracer PET-CT findings) and (b) control (showing both FDG and ⁶⁸Ga-DOTATATE uptake). The cohort was divided based on dual tracer PET-CT into: (i) metabolically FDG non-avid and SSTR expressing tumors, (ii) metabolically active and non-⁶⁸Ga-DOTATATE concentrating (SSTR expressing) and (iii) matched imaging characteristics with WHO 2017 grading system (showing both FDG and ⁶⁸Ga-DOTATATE concentrating disease) for statistical analysis. Statistical analyses were done on SPSS 23.0. Descriptive statistics was used to analyze categorical data, multivariate analysis was used to assess the correlation between different variables with progression free survival (PFS) and overall survival (OS). Kaplan-Meier was used for survival analysis to calculate median survival and to analyze the survival based on WHO 2017 grading and dual tracer PET. Cox proportional hazards regression analysis was used to determine predictors of survival (OS and PFS). Results: In the entire cohort (n = 36), 24 patients (66.7%) showed discordance whereas 12 patients (33.3%) were in the control group. Among the patients showing discordance: 14 patients (38.9%) had metabolically inactive and SSTR expressing disease and remaining 10 patients (27.8%) had FDG concentrating and SSTR non-expressing disease. Those in the control group, 12 patients (33.3%) had intermediate grade NETs and showed matched (⁶⁸Ga-DOTATATE and FDG concentrating lesions) disease. Multivariate analysis in patients with discordant findings demonstrated significant correlation of dual tracer PET with overall survival while no significant correlation could be established between WHO grade and overall survival in the discordant subgroups. No significant correlation could be appreciated between PFS and either dual tracer PET or WHO grading. The Kaplan-Meier survival analysis and Cox proportional hazards regression analysis demonstrated dual tracer PET-CT imaging to be significant prognostic determinant and predictor of outcome respectively. Conclusion: In summary, in NET patients with discordance between the two parameters, dual tracer PET-CT with FDG and ⁶⁸Ga-DOTATATE performed better than WHO grading, differentiation status and immunohistochemistry in prognosticating and predicting outcome.

Peptide Receptor Radionuclide Therapy in the Management of Neuroendocrine Tumors (Neoplasms): Fundamentals and Salient Clinical Practice Points for Medical Oncologists

This editorial commentary is an expert summary of “Peptide Receptor Radionuclide Therapy (PRRT),” encompassing the essential fundamentals and salient clinical practice points, deliberated and designed in a point-wise manner with theme-based subheadings. Emphasis has been laid on the topics of practical relevance to the referring oncologists with relevant finer points where necessary. A part of the presented overview has been generated from the authors' own practical experience of more than 3500 successful therapies delivered over the last 9 years at a large tertiary care PRRT setting by the joint efforts of Radiation Medicine Centre (RMC), Bhabha Atomic Research Centre (BARC), and Gastrointestinal services of Tata Memorial Hospital (TMH) at the TMH-RMC premises. While the technical indigenization is beyond the scope of this treatise, we must mention here that India had been one of the frontrunners in this treatment modality, and the PRRT services in this country were developed purely as an indigenous effort right from the production of the radionuclide (177-Lutetium) at the reactor and radiolabeling and production of the radiopharmaceutical (177Lu-DOTATATE) by the radiopharmaceutical scientists at the BARC and RMC; such an endeavor allowed this very specialized therapy to be delivered at a very affordable cost in our setting which could be viewed as a major societal contribution of the atomic energy research in this country.

Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT), over the years, has evolved as an important modality in the therapeutic armamentarium of advanced, metastatic or inoperable, progressive Neuroendocrine Neoplasms (NENs). This review deliberates on the basic understanding and applied clinical aspects of PRRT in NENs, with special reference to (1) tumor biology and receptor characteristics, (2) molecular PET-CT imaging (in particular the invaluable role of dual-tracer PET with [68Ga]-DOTA-TATE/NOC and [18F]-FDG for exploring tumor biology in continuum and individualizing treatment decision making) and NEN theranostics, (3) relevant radiochemistry of different therapeutic radionuclides (both beta emitting 177Lu-DOTATATE and 90Y-DOTATATE and alpha emitting 225Ac-DOTATATE), and (4) related dosimetric considerations. Successful clinical management of the NENs would require multifactorial considerations, and all the aforementioned points pertaining to the disease process and available logistics are key considerations for state-of-the-art clinical practice and delivering personalized care in this group of patients. Emphasis has been placed on relatively intriguing areas such as (1) NET grade 3 of WHO 2017 classification (ie, Ki-67>20% but well-differentiation features), (2) "Neoadjuvant PRRT," (3) combining chemotherapy and PRRT, (4) 'Sandwich Chemo-PRRT', (5) duo-PRRT and tandem PRRT, (6) resistant functioning disease with nuances in clinical management and how one can advocate PRRT rationally in such clinical settings and individualize the management in a patient specific manner. Relevant clinical management issues related to some difficult case scenarios, which the Nuclear Medicine attending physician should be aware of to run an efficient clinical PRRT services, are described.

Diagnostic Approaches to Neuroendocrine Neoplasms of Unknown Primary Site

Neuroendocrine neoplasms (NENs) arise from cells of neuronal and endocrine differentiation. While they are a rare entity, an increasing proportion of patients with NEN present with metastatic disease and no evident primary site using routine imaging or histopathology. NENs of unknown primary site have a poorer prognosis, often due to the challenge of selecting appropriate evidence-based management. We review the available literature and guidelines for the management of NENs of unknown primary site including clinical features, biochemical tests, histopathology, imaging, surgical exploration and localised and systemic treatments. We also discuss novel molecular techniques currently under investigation to aid primary site identification.

Predictive Value of 99MTC-hynic-toc Scintigraphy in Lung Neuroendocrine Tumor Diagnosis

Background:

Νeuroendocrine tumors of the lungs are rare arising in the thymus and gastro-entero-pancreatic tract and belonging to foregut of neuroendocrine tumors. The aim of the present prospective study was to estimate the potential impact of single-photon emission computed tomography somatostatin receptor scintigraphy using 99mTc-Tektrotyd on diagnosis, treatment response, and prognosis in patients with neuroendocrine tumors of the lungs.

Methods:

Thirty-six patients with neuroendocrine tumors of the lungs were evaluated by using 99mTc-HYNIC-TOC scintigraphy. The scintigraphic results were compared to liver tissue uptake (Krenning score). Likewise, the functional imaging results were compared with biochemical indices including chromogranin A, neuroendocrine-specific enolase, and insulin-like growth factor 1 at the time of diagnosis (baseline) and disease progression.

Results:

The number of somatostatin receptors, expressed with Krenning score, did not show any correlation with the survival of patients both at baseline (P = .08) and at disease progression (P = .24), and scintigraphy results did not relate significantly to progression-free survival. Comparing the results of 99mTc-HYNIC-TOC scintigraphy according to the response of patients in the initial treatment, a statistically significant negative correlation was observed both in the first and in the second scintigraphy with patients’ response (P = .001 and P < .001, respectively). The concentrations of biochemical markers were in accordance with scintigraphy results in the diagnosis.

Conclusion:

This study indicates that 99mTc-HYNIC-TOC scintigraphy appears to be a reliable, noninvasive technique for detection of primary neuroendocrine tumors and their locoregional or distant metastases, although it cannot be used as a neuroendocrine tumors of the lungs predictive technique.

Implications of fluorodeoxyglucose uptake in low-intermediate grade metastatic neuroendocrine tumors from peptide receptor radionuclide therapy outcome viewpoint: A semi-quantitative standardized uptake value-based analysis

Dual tracer positron emission tomography (PET) imaging approach (with ⁶⁸Ga-DOTATATE PET-computed tomography (CT) for somatostatin receptor and 18-fluorodeoxyglucose (¹⁸FDG) PET-CT for glucose transporter receptor) plays a vital role in baseline differentiation, treatment decision-making, and prognostic assessment of neuroendocrine tumors (NETs). The aims of this study were to observe and compare the clinical behavior of low-/intermediate-grade NETs depending on their baseline FDG metabolism (calculated through pre-peptide receptor radionuclide therapy [PRRT] FDG standardized uptake value [SUV]) and to determine its prognostic importance in predicting extent of therapeutic response (post-PRRT) in terms of symptomatic, biochemical, and scan parameters along with the long-term impact on progression-free survival (PFS) and overall survival (OS). Fifty-nine patients with low (≤2%) and intermediate (3–20% Mib-1/Ki-67 index) grade metastatic NET were selected for this retrospective analysis and divided into three groups: Group 1 consisted of patients having low-grade FDG uptake at baseline, predefined as SUV_max< 5 (n = 13); Group 2 consisted of those having intermediate-grade FDG uptake at baseline, SUV_max5–10 (n = 34), and Group 3 consisted of patients having high-grade FDG uptake at baseline, defined as SUV_max>10 (n = 12). The trend of FDG avidity was studied from the baseline till the time of analysis and the overall outcomes were compared in terms of symptomatic response (Karnofsky and ECOG performance score), biochemical response, scan response (anatomical and metabolic, RECIST 1.1 and PERCIST 1.0), PFS and OS. Patients in Groups 1 and 2 showed highest proportion of symptomatic complete response, biochemical partial response, and stable disease on scan. These patients also demonstrated better PFS and OS and lowest hazard ratio compared to patients in the Group 3. An important finding was a substantial fraction of the complete metabolic responders (CMRs) across the groups, achieved CMR within first 2 cycles of PRRT (85% of Group 1, 51% of Group 2, and 47% of Group 3). In conclusion, most of the patients of low-/intermediate-grade NET having low-to-moderate baseline tumor FDG metabolism (SUV_max≤10) showed favorable symptomatic response with good biochemical and anatomical disease control and were associated with prolonged PFS and OS, compared to that of those having high-grade baseline tumor FDG metabolism (SUV_max>10).

PET/CT Evaluation of Head and Neck Cancer of Unknown Primary

The diagnosis of carcinoma of unknown primary in the head and neck is made when there is a metastasis but no primary lesion is identified after physical exam and diagnostic CT or MR imaging. PET/CT is the first step in searching for a primary lesion, followed by more invasive techniques such as endoscopy and surgery. Knowledge of the different tumor histologic types, preferential locations of nodal spread, imaging pitfalls, and other special considerations such as cystic metastases can be helpful in the ultimate identification of primary tumors, which leads to improved overall patient survival.

Prognostic value of somatostatin receptor expressing tumor volume calculated from 68Ga-DOTATATE PET/CT in patients with well-differentiated neuroendocrine tumors

PURPOSE

To evaluate the prognostic value of volumetric parameters calculated from ⁶⁸Ga-1,4,7,10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA)-Thr³-octreotate (⁶⁸Ga-DOTATATE) positron emission tomography/computed tomography (PET/CT) in patients with well-differentiated neuroendocrine tumor (WD-NET).

METHODS

Ninety-two patients (44 men and 48 women, mean age of 59.5-year-old) with pathologically confirmed WD-NET (grades 1 or 2) were enrolled in a prospective expanded access protocol. Selected data was analyzed retrospectively for this project. Maximum standardized uptake value (SUV_max) in the lesion with the highest ⁶⁸Ga-DOTATATE uptake was measured and recorded for each patient. In addition, two volumetric parameters, namely, somatostatin receptor expressing tumor volume (SRETV) and total lesion somatostatin receptor expression (TLSRE), were calculated in each ⁶⁸Ga-DOTATATE-avid lesion. SRETV was defined as tumor volume with higher ⁶⁸Ga-DOTATATE uptake than the 50% of SUV_max within the volume of interest (VOI) for each lesion. TLSRE was calculated by multiplying SRETV and mean SUV within the same VOI. Thereafter, the sum of SRETV (ΣSRETV) and TLSRE (ΣTLSRE) for all detected lesions per patient were calculated. Progression-free survival (PFS) was set as primary endpoint. Kaplan-Meier survival analysis, log-rank test, and Cox's proportional hazard model were used for statistical analysis.

RESULTS

Univariate analyses revealed significant difference of PFS for WHO tumor grade and ΣSRETV (P < 0.05), while there were no significant differences in age, sex, SUV_max, and ΣTLSRE (P > 0.05). Multivariate analysis identified WHO tumor grade and ΣSRETV as independent predictors of PFS.

CONCLUSION

ΣSRETV calculated from ⁶⁸Ga-DOTATATE PET/CT may have prognostic value of PFS in WD-NET patients.

Detection rate of unknown primary tumour by using somatostatin receptor PET/CT in patients with metastatic neuroendocrine tumours: a meta-analysis

PURPOSE

The high diagnostic performance of somatostatin receptor positron emission tomography with computed tomography (PET/CT) in neuroendocrine tumours (NETs) was demonstrated by several articles. However, only some studies evaluated the detection rate (DR) of this imaging method in patients with metastatic NETs and unknown primary tumours (CUP-NETs). Therefore, we aimed to perform a meta-analysis to add evidence-based data in this setting.

METHODS

A comprehensive computer literature search of studies listed in PubMed/MEDLINE, EMBASE, and Cochrane library databases through December 2018 and regarding the use of somatostatin receptor PET/CT in patients with CUP-NETs was carried out. Pooled DR of CUP-NETs by using somatostatin receptor PET/CT was calculated. A pooled analysis evaluating the percentage of change of management by using somatostatin receptor PET/CT in these patients was also performed.

RESULTS

Twelve studies on the use of somatostatin receptor PET/CT in detecting CUP-NETs in 383 metastatic patients were included. The meta-analysis of all these studies provided the following DR on a per patient-based analysis: 56% (95% confidence interval (95% CI): 48-63%). Moderate heterogeneity among the selected studies was found (I² = 50%), whereas a significant publication bias was excluded by Egger's test (p = 0.45). The most common primary tumour sites were the bowel and the pancreas. A change of management by using somatostatin receptor PET/CT was demonstrated in 20% (95% CI: 10-33%) of patients with CUP-NET.

CONCLUSIONS

Somatostatin receptor PET/CT is very useful in detecting CUP-NETs in patients with metastatic disease. More studies on the change of management by using this imaging method in this setting are needed.

Cerebellar Metastasis of Unknown Primary Neuroendocrine Carcinoma: Report of Case Mimicking Hemangioblastoma

BACKGROUND

Neuroendocrine carcinoma (NEC) originates with neuroendocrine cells and is mainly found in the pancreas, lungs and gastrointestinal tract. We surgically treated a case of primary unknown NEC with only cerebral metastasis that mimicked hemangioblastoma. Recurrence was seen at the fornix, and no primary lesion had been identified as of 2 years after treatments despite careful examination.

CASE DESCRIPTION

A 61-year-old man presented with dizziness. Past medical history included hypertension, dyslipidemia, hyperuricemia and colon polyp. We performed magnetic resonance imaging (MRI) to examine the cause of dizziness, revealing tumor with enhancement and peritumoral edema at the right cerebral lesion. Contrast-enhanced whole-body computed tomography (CT) showed no other lesions. We suspected hemangioblastoma from examinations and decided on surgical resection. Neuropathologically, the resected tumor was diagnosed as brain metastasis of NEC, but CT, fluorodeoxyglucose-positron emission tomography, gastrointestinal endoscopy, and somatostatin receptor scintigraphy all failed to reveal the primary lesion. As postoperative MRI showed enhancement around the resection cavity and at the right fornix, radiotherapy was performed. No other lesions were seen at 24 months postoperatively. We are continuing careful monitoring and no chemotherapy has been administered.

CONCLUSIONS

We treated brain metastasis from NEC of unknown primary and mimicking hemangioblastoma using only local treatment. When an enhancing, single, solid tumor is seen in the cerebellum, brain metastasis from NEC of unknown primary is 1 differential diagnosis.

Current concepts in the diagnosis and management of neuroendocrine neoplasms of unknown primary origin

Neuroendocrine neoplasms (NENs) of unknown primary origin (UPO-NENs) are advanced neoplasms constituting 11-22% of all NENs that by definition their primary tissue of origin has not been identified with standard diagnostic work-up. Delineating the primary site of origin of UPO-NENs has important implications for selecting the appropriate treatment and overall prognosis. The small bowel, followed by the lung and pancreas are the most prevalent primary sites of origin of UPO-NENs that are uncovered during an extensive and prolonged diagnostic work-up; however, a number of UPO-NENs may still remain occult even after prolonged follow-up. A number of diagnostic algorithms that incorporate histopathological, molecular, imaging (either morphological or functional imaging), and serum biomarkers can help to identify the primary tumor origin. It is expected that advances in these fields will help reduce significantly the number of UPO-NENs.

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.

Management of neuroendocrine tumors of unknown primary

Neuroendocrine neoplams (NENs) are mostly relatively indolent malignancies but a significant number have metastatic disease at diagnosis mainly to the liver. Although in the majority of such cases the primary origin of the tumor can be identified, in approximately 11-22% no primary tumor is found and such cases are designated as NENs of unknown primary origin (UPO). This has significant therapeutic implications with respect to potentially resectable hepatic disease and/or application of appropriate medical therapy, either chemotherapeutic agents or targeted treatment, as the response to various treatments varies according to the origin of the primary tumor. This lack of tumor specific orientated treatment may also account for the relatively poorer prognosis of NENs of UPO compared to metastatic NENs with a known primary site. In the majority of cases the primary tumors are located in the small bowel and the lung, but a number may still elude detection. Occasionally the presence of a functional syndrome may direct to the specific tissue of origin but in the majority of cases a number of biochemical, imaging, histopathological and molecular modalities are utilized to help identify the primary origin of the tumor and direct treatment accordingly. Several diagnostic algorithms have recently been developed to help localize an occult primary tumor; however, in a number of cases no lesion is identified even after prolonged follow-up. It is expected that the delineation of the molecular signature of the different NENs may help identify such cases and provide appropriate treatment.

Classification of pulmonary neuroendocrine tumors: new insights

Neuroendocrine tumors of the lung (Lu-NETs) embrace a heterogeneous family of neoplasms classified into four histological variants, namely typical carcinoid (TC), atypical carcinoid (AC), large cell neuroendocrine carcinoma (LCNEC) and small cell lung carcinoma (SCLC). Defining criteria on resection specimens include mitotic count in 2 mm2 and the presence or absence of necrosis, alongside a constellation of cytological and histological traits including cell size and shape, nuclear features and overall architecture. Clinically, TC are low-grade malignant tumors, AC intermediate-grade malignant tumors and SCLC/LCNEC high-grade malignant full-blown carcinomas with no significant differences in survival between them. Homologous tumors arise in the thymus that occasionally have some difficulties in differentiating from the lung counterparts when presented with large unresectable or metastatic lesions. Immunohistochemistry (IHC) helps refine NE diagnosis at various anatomical sites, particularly on small-sized tissue material, in which only TC and small cell carcinoma categories can be recognized easily on hematoxylin & eosin stain, while AC and LCNEC can only be suggested on such material. The Ki-67 labeling index effectively separates carcinoids from small cell carcinoma and may prove useful for the clinical management of a metastatic disease to help the therapeutic decision-making process. Although carcinoids and high-grade neuroendocrine carcinomas in the lung and elsewhere make up separate tumor categories on molecular grounds, emerging data supports the concept of secondary high-grade NETs arising in the preexisting carcinoids, whose clinical and biological relevance will have to be placed into the proper context for the optimal management of these patients. In this review, we will discuss the selected, recent literature with a focus on current issues regarding Lu-NET nosology, i.e., classification, derivation and tumor evolution.