Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects

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

Evaluation of the prognosis for N2 status in patients with small bowel neuroendocrine tumors

BACKGROUND

The 8th edition AJCC Staging for small bowel neuroendocrine tumors created a novel N2 classification. This study investigates if it is independently prognostic.

METHODS

Records of patients from 2008 to 2019 were reviewed. Survival rates were estimated by Kaplan-Meier method and compared by log-rank. The Cox Proportional Hazards model was used to determine factors associated with overall survival (OS) via multivariate analysis.

RESULTS

Among 300 patients, 225 were N2 and 60 were N1. No differences were seen in pathologic markers for N1 compared to N2. N2 were more likely to have liver metastases (LM) (p = 0.048) but rates of resectability were similar. Median OS for N1 with >70% liver cytoreduction was not yet reached compared to 121 months for N2 (p = 0.005). On multivariate analysis, LM was associated with shorter survival (p = 0.028), but nodal status was not.

CONCLUSIONS

Unlike LM, N2 status is not independently prognostic, but a marker for aggressive LM.

Home Total Parenteral Nutrition for Intestinal Failure in Patients with Advanced Small Intestinal Neuroendocrine Neoplasms

The role of total parenteral nutrition (TPN) in cancer patients is controversial, but it may be a treatment option for some patients with indolent but advanced small intestinal neuroendocrine neoplasms (SI-NENs). The aim of this study is to investigate whether home TPN was associated with long-term survival and to assess the indications, duration and complications of TPN in patients with advanced SI-NENs. Patients with advanced SI-NENs who received home TPN were retrospectively included. Electronic records were reviewed for clinical information. Five patients receiving home TPN were identified out of 1011 patients with SI-NENs in our center. The median duration of TPN administration was 12 mo. Small bowel obstruction was the most common reason for TPN initiation. TPN-related complications included two catheter infections, one thrombosis and one episode of TPN-related transaminitis. At the last follow-up, three patients had died and two were alive. The median survival was 12 mo. Overall estimated 1-yr probability of survival on home TPN by Kaplan-Meier analysis was 40%. In conclusion, home TPN may be a treatment option in highly selected advanced SI-NEN patients with severe gastrointestinal tract dysfunction. The initiation of home TPN is associated with long-term survival (≥1 yr), and complication rates appear acceptable.

Evaluation of circulating transcript analysis (NETest) in small intestinal neuroendocrine neoplasms after surgical resection

PURPOSE

Surgical resection is the only effective curative strategy for small intestinal neuroendocrine neoplasms (SINENs). Nevertheless, the evaluation of residual disease and prediction of disease recurrence/progression remains a problematic issue.

METHODS

We evaluated 13 SINENs that underwent surgical resection of the primary tumour and/or mesenteric mass. Patients were divided in three groups: (a) Group 1: SINENs that underwent resection with curative intent, (b) Group 2: SINENs treated with resection in the setting of metastatic disease, which remained stable and (c) Group 3: SINENs treated with resection in the setting of metastatic disease, with evidence of any progression at follow-up. NETest and chromogranin A were measured pre-operatively and post-operatively during a 22-month median follow-up period and compared with imaging studies. NETest score <20% was determined as normal, 20-40% low, 41-79% intermediate and ≥80% high score.

RESULTS

NETest score was raised in all (100%) SINENs pre-operatively. Surgery with curative intent resulted in NETest score reduction from 78.25 ± 15.32 to 25.25 ± 1.75 (p < 0.05). Low NETest scores post-operatively were evident in all cases without clinical evidence of residual disease (Group 1). However, the low disease activity score suggested the presence of microscopic residual disease. In three cases (75%) with stable disease (Group 2) the NETest score was low consistent with indolent disease. In the progressive disease group (Group 3), a high NETest score was present in three cases (60%) and an intermediate NETest score in the remainder (40%).

CONCLUSIONS

Blood NETest scores accurately identified SINENs and were significantly decreased by curative surgery. Monitoring NETest post-operatively may facilitate management by identifying the presence of residual/progressive disease.

Surgical Management of Primary Small Bowel NET Presenting Acutely with Obstruction or Perforation

Up to 35% of small bowel neuroendocrine tumors (SBNETs) may present with an acute intra-abdominal complication including obstruction, perforation, bleeding or ischemia and may require emergency surgical treatment in centers not normally accustomed to managing patients with neuroendocrine tumors. These patients may have a known diagnosis of SBNET, be suspected as suffering from SBNET or have SBNET diagnosed as an incidental finding on presenting radiology or postoperative pathology. Perioperative priorities include obtaining both clinical and radiological staging with cross-sectional imaging and clinical examination, screening for the presence of carcinoid syndrome and right-sided cardiac disease and assessment of prognosis. Intraoperatively careful attention should be paid to noting the presence and location of multifocal primary and metastatic disease. Ideally, surgical resection with mesenteric lymph node dissection is the treatment of choice for obstructing and perforating lesions. Extended lymphadenectomy along the SMA, SMV and behind the pancreas should be primarily considered an elective procedure. In unwell patients with advanced disease surgical bypass (jejuno or ileocolic) or proximal defunctioning should be undertaken but, given the excellent long-term survivals in patients with stage IV disease, could be considered bridging procedures to elective resection following formal staging and multidisciplinary review.

Magnetic Resonance of Small Bowel Tumors

Tumors of the small intestine represent less than 5% of all gastrointestinal tract neoplasms. Magnetic resonance (MR) imaging is rapidly increasing clinical acceptance to evaluate the small bowel and can be the initial imaging method to investigate small bowel diseases. MR examinations may provide the first opportunity to detect and characterize tumors of the small bowel. Intraluminal and extraluminal MR findings, combined with contrast enhancement and functional information, allow accurate diagnoses and consequently characterization of small bowel neoplasms. This article describes the MR findings of primary small bowel neoplasms and the MR findings for the differential diagnosis are discussed.

Multimodality Imaging of Ileal Neuroendocrine (Carcinoid) Tumor

OBJECTIVE. The purpose of this article is to provide a multimodality imaging review of ileal carcinoid tumor. CONCLUSION. Ileal carcinoid tumors display a variety of radiologic findings. Delay in diagnosis is common because of initial nonspecific symptoms and subtle imaging findings. Reviewing the multimodality imaging appearance of the primary tumor, metastatic disease, and associated ancillary findings can help improve patient care.

Usefulness of Capsule Endoscopy and Double-balloon Enteroscopy for the Diagnosis of Multiple Carcinoid Tumors in the Small Intestine: Case Reports and a Literature Review

The incidence of carcinoid tumor in the small intestine is increasing; however, its preoperative diagnosis is difficult. We recently experienced three cases of multiple carcinoid tumors in the small intestine successfully detected using capsule endoscopy (CE), followed by a pathological diagnosis using double-balloon enteroscopy (DBE). To diagnose multiple carcinoid in the small intestine appropriately, we reviewed the information of five cases reported to date along with our three recent cases. The literature review demonstrated that CE and DBE are useful for detecting and diagnosing small intestinal carcinoids and tumor multiplicity, which aids in determining the appropriate resection range.

Tumor Cystic Necrosis Following Peptide Receptor Radionuclide Therapy in Neuroendocrine Tumors

The response assessment to peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumors is complex. We present the case of a 49-year-old man with metastatic rectal neuroendocrine tumor whose clinical symptoms and response evaluation criteria in solid tumors suggested progressive disease following PRRT. However, Ga-DOTA-(Tyr3)-octreotate PET/CT showed a partial scintigraphic response with absence of F-FDG PET/CT uptake consistent with tumor cystic necrosis. Long-term follow-up confirmed ongoing tumor response to treatment. Utilizing all modalities of response assessment seems to be important in correctly judging the benefit from PRRT and will need to be incorporated when developing response assessment tools.

Hindgut gastropancreatic neuroendocrine carcinoma mimicking hydatid disease

Primary neuroendocrine tumors of the colon are usually very rare and difficult to spot on a nonfunctional imaging. Metastatic lesions are mostly hypervascular, with only a small percentage appearing as cystic or hypovascular lesions. We present a case of a 34-year-old Hispanic female with a history of dull aching upper abdominal pain lasting for a few months. Initial abdominal ultrasound revealed multiple cystic lesions replacing the hepatic parenchyma concerning for a hydatid disease. Liver biopsy was obtained due to negative serology for hydatid disease, which surprisingly revealed a metastatic neuroendocrine tumor of unknown etiology. The primary disease was depicted within the sigmoid colon on a whole-body Octreotide single-photon emission computed tomography-computed tomography done following the biopsy.

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

Imaging is critical in the diagnosis, prognosis, and management of neuroendocrine tumors (NETs). NETs share common imaging features, but each type exhibits unique features. Computed tomography scans or MRI of the abdomen is used to assess tumor burden routinely. Functional imaging with octreotide scan or gallium-68 somatostatin analog PET is used selectively to confirm diagnosis and guide therapy. Clinicians and radiologists should be familiar with the indications and interpretations of imaging modalities. Novel functional imaging modalities likely will be developed to detect small NETs, predict prognosis, guide therapeutic choices, and design novel therapies.

Biochemical Diagnosis and Preoperative Imaging of Gastroenteropancreatic Neuroendocrine Tumors

Neuroendocrine tumors are a group of neoplasms that can arise in a variety of locations throughout the body and often metastasize early. A patient's only chance for cure is surgical removal of the primary tumor and all associated metastases, although even when surgical cure is unlikely, patients can benefit from surgical debulking. A thorough preoperative workup will often require multiple clinical tests and imaging studies to locate the primary tumor, delineate the extent of the disease, and assess tumor functionality. This review discusses the biomarkers important for the diagnosis of these tumors and the imaging modalities needed.

Ileal neuroendocrine tumors and heart: not only valvular consequences

Ileal neuroendocrine tumors (NETs) often progress slowly, but because of their generally nonspecific symptoms, they have often metastasized to local lymph nodes and to the liver by the time the patient presents. Biochemically, most of these patients have increased levels of whole blood serotonin, urinary 5-hydroxyindoleacetic acid, and chromogranin A. Imaging work-up generally comprises computed tomography or magnetic resonance imaging and somatostatin receptor scintigraphy, or in recent years positron emission tomography with 68Ga-labeled somatostatin analogs, allowing for detection of even sub-cm lesions. Carcinoid heart disease with affected leaflets, mainly to the right side of the heart, is a well-known complication and patients routinely undergo echocardiography to diagnose and monitor this. Multitasking surgery is currently recognized as first-line treatment for ileal NETs with metastases and carcinoid heart disease. Open heart surgery and valve replacement are advocated in patients with valvular disease and progressive heart failure. When valvulopathy in the tricuspid valve results in right-sided heart failure, a sequential approach, performing valve replacement first before intra-abdominal tumor-reductive procedures are conducted, reduces the risk of bleeding. Metastases to the myocardium from ileal NETs are seen in <1-4.3% of patients, depending partly on the imaging technique used, and are generally discovered in those affected with widespread disease. Systemic treatment with somatostatin analogs, and sometimes alpha interferon, is first-line medical therapy in metastatic disease to relieve hormonal symptoms and stabilize the tumor. This treatment is also indicated when heart metastases are detected, with the addition of diuretics and fluid restriction in cases of heart failure. Myocardial metastases are rarely treated by surgical resection.

MRI of uncommon lesions of the large bowel: a pictorial essay

This pictorial essay briefly discusses methods for optimizing bowel imaging with magnetic resonance imaging (MRI) and illustrates the MRI appearance of a variety of unusual lesions involving or related specifically to the large bowel.

Hypervascular mediastinal masses: action points for radiologists

Hypervascular mediastinal masses are a distinct group of rare diseases that include a subset of benign and malignant entities. Characteristic features and known association with syndromes and genetic mutations assist in achieving a diagnosis. Imaging allows an understanding of the vascularity of the lesion and should alert the radiologist and clinician to potential hemorrhagic complications and avoid percutaneous CT guided biopsies. In such cases, pre-procedure embolization and surgical biopsy maybe considered for better control of post procedure hemorrhage. The purpose of this article is to describe and illustrate the clinical features and radiologic spectrum of hypervascular mediastinal masses, and discuss the associated clinical and genetic syndromes. We will present an imaging algorithm to determine further evaluation and subsequently guide treatment.