[Receptor scintigraphy in endocrine gastrointestinal and pancreatic tumors]

[PET-CT for neuroendocrine tumors and nuclear medicine therapy options]

Neuroendocrine tumors (NET) are defined by biochemical characteristics and structures which can be specifically addressed by radioligands for diagnostic imaging as well as radionuclide therapy in nuclear medicine. Somatostatin receptor imaging has been shown to be an important part of the diagnostic process in the management of NET for a long time. In recent years a number of tracers enabling PET-based imaging of somatostatin receptors and amine precursor uptake have been developed. By combining the specific functional information of the PET signal with anatomical information by CT imaging using PET-CT hybrid scanners, primary tumors and metastases can be detected with high resolution and high sensitivity. Compared with conventional indium-111 octreotide scintigraphy PET-CT has a higher resolution and also a lower radiation exposure. In addition, quantification of the tracer uptake allows therapy monitoring. By labelling with therapeutic beta-emitters, such as lutetium-177 or yttrium-90, a systemic internal radiotherapy with somotostatin analogues (peptide radionuclide radiation therapy, PRRT) can be provided as a therapeutic option for patients with unresectable and metastasized neuroendocrine tumors.

Scintigraphic detection of carcinoid tumors with a cost effectiveness analysis

AIM: To evaluate the diagnostic sensitivity and accuracy and the cost-effectiveness of this technique in the detection of gastroenteropancreatic carcinoid tumors and their metastases in comparison with conventional imaging methods.

METHODS: Somatostatin receptor scintigraphy (SRS) was performed in 24 patients with confirmed carcinoids and 7 under investigation. The results were compared with those of conventional imaging methods (chest X-ray, upper abdominal ultrasound, chest CT, upper and lower abdominal CT). Also a cost-effectiveness analysis was performed comparing the cost in Euro of several combinations of SRS with conventional imaging modalities.

RESULTS: SRS visualized primary or metastatic sites in 71.0% of cases and 61.3% of conventional imagings. The diagnostic sensitivity of the method was higher in patients with suspected lesions (85.7% vs 57.1%). SRS was less sensitive in the detection of metastatic sites (78.9% vs 84.2%). The undetectable lesions by SRS metastatic sites were all in the liver. Between several imaging combinations, the combinations of chest X-ray/upper abdominal CT/SRS and chest CT/upper abdominal CT/SRS showed the highest sensitivity (88.75%) in terms of the number of detected lesions. The combinations of chest X-ray/upper abdominal US/SRS and chest CT/upper abdominal ultrasound/SRS yielded also a quite similar sensitivity (82%). Compared to the cost of the four sensitive combinations the combination of chest X-ray/upper abdominal ultrasound/SRS presented the lower cost, 1183.99 Euro vs 1251.75 Euro for chest CT/upper abdominal ultrasound/SRS, 1294.93 Euro for chest X/ray/upper abdominal CT/SRS and 1362.75 Euro for chest CT/upper abdominal CT/SRS.

CONCLUSION: SRS imaging is a very sensitive method for the detection of gastroenteropancreatic carcinoids but is less sensitive than ultrasound and CT in the detection of liver metastases. Between several imaging combinations, the combination of chest X-ray/upper abdominal CT/SRS shows the highest sensitivity with a cost of 1294.93 Euro.

[Clinical value of somatostatin receptor scintigraphy. Studies of pre- and intraoperative localization of gastrointestinal and pancreatic tumors]

BACKGROUND

[111In-DTPA-D-Phe1]-pentetreotide scintigraphy is able to detect neuroendocrine tumors not shown by radiological methods.

PATIENTS AND METHODS

In 270 patients with neuroendocrine gastroenteropancreatic tumors (GEP tumors) 400 somatostatin receptor scintigraphies were performed. 70 patients (38 female, 32 male, aged 28 to 74 [56 +/- 12.6] years) underwent surgery and follow-up over 2 years. The aim of the present study was the comparison of preoperative somatostatin receptor scintigraphy with radiological methods (sonography, CT) and intraoperative localization of GEP tumors with a hand-held gamma-probe.

RESULTS

Somatostatin receptor scintigraphy was successful in localizing primary tumors in all patients. Liver- and lymph node metastases could be visualized with a sensitivity of 94 and 95 percent. In 7 patients 35 lesions could be identified by intraoperative tumor localization using a hand held gamma probe. Radiological methods identified only 11, surgical palpation 15 and preoperative somatostatin receptor scintigraphy 27 lesions.

CONCLUSION

Somatostatin receptor scintigraphy improves detection of small and occult GEP tumors. Intraoperative probe counting with a hand-held gamma probe can identify tumors even when they are small and impalpable, but receptor positive.

Vasoactive intestinal polypeptide-secreting tumours: biology and therapy

VIP-secreting tumours are rare, but they produce a dramatic clinical picture, the most prominent feature being profuse, watery diarrhoea and hypokalaemia. VIPomas are malignant and require sophisticated diagnostic and localization techniques in order to identify their presence. Delays in diagnosis are the rule rather than the exception. Improvements in the diagnosis of VIPomas appear to result in an increase in resectability rates. A definitive diagnosis is aided by the determination of plasma VIP concentrations through the use of sensitive radioimmunoassays. With heightened awareness of this syndrome, increasing numbers of patients can be identified and more effective treatments developed for the refractory and recurrent tumours.

Endoscopic ultrasonography and somatostatin receptor scintigraphy in the preoperative localisation of insulinomas and gastrinomas

BACKGROUND

Endoscopic ultrasonography (EUS) and somatostatin receptor scintigraphy (SRS) can detect a high percentage of gastroenteropancreatic neuroendocrine tumours especially in the upper gastrointestinal tract. The ability of these procedures to localise primary tumour lesions and metastases of gastrinomas and insulinomas was evaluated in comparison with transabdominal ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI).

PATIENTS AND METHODS

In a prospective trial, patients with gastrinomas (n = 10) and insulinomas (n = 10) diagnosed by clinical signs and laboratory tests were assessed by EUS, SRS, US, CT and MRI.

RESULTS

In 10 patients with gastrinoma and 10 patients with insulinoma, a total of 14 separate primary tumour lesions were histologically confirmed for each of the tumour entities. The mean diameter was 2.1 cm for gastrinomas and 1.5 cm for insulinomas. All insulinomas and nine gastrinoma lesions were located in the pancreas. Three gastrinomas were found in the duodenal wall, one in a periduodenal lymph node, and one in the liver, For gastrinomas, sensitivities were 79% with EUS, 86% with SRS and 29% with CT, US, and MRI. For insulinomas, sensitivities were 93% with EUS, 14% with SRS, 21% with CT and 7% with US and MRI.

CONCLUSIONS

EUS is of high value for localising primary lesions of both tumour entities. SRS is a very sensitive procedure for diagnosing of gastrinomas but not insulinomas. CT, US and MRI are primarily useful for visualising metastases.

The diagnostic utility of somatostatin receptor scintigraphy in oncology

Somatostatin receptor scintigraphy (SRS) with the diethylenetriaminopentaacetic-acid-conjugated somatostatin analogue [111In-DTPA-D-Phe1] octreotide, also known as 111In-pentetreotide, is a new non-invasive modality for the evaluation of tumours that express receptors for somatostatin. These receptors are present on neuroendocrine and other tumours, including lymphomas and some breast cancers. In oncology SRS is a promising diagnostic tool for localizing primary tumours, staging, control and follow-up after therapy, and for identification of patients who may benefit from therapy with unlabelled octreotide or, in the future, with radiolabelled octreotide. In the past few years many small and large studies investigating various aspects of SRS have been reported. In this review the value of SRS in the management of individual tumour types is explored. For many tumours the best sensitivity in lesion detection is only achieved by very careful imaging after the administration of at least 200 MBq 111In-pentetreotide. On the basis of the current experience the main value of SRS in oncology is in the staging and evaluation of gastroenteropancreatic tumours, paragangliomas, small-cell lung cancer and lymphomas. Promising areas for SRS are the evaluation of breast cancer, non-medullary thyroid cancer and melanoma, and initial results with targeted radionuclide therapy using radiolabelled octreotide have been reported.

Preliminary evaluation of the usefulness of Tc-99m (V) DMSA in pancreatic neuroendocrine tumors

The authors describe the possible application of Tc-99m (V) DMSA scintigraphy in pancreatic neuroendocrine tumors. In consideration of the common embryonic origin of these tumors and other neoplastic diseases (medullary thyroid carcinoma, pheocromocytoma, neuroblastoma) that have been well studied with radionuclide imaging, five cases of pancreatic neuroendocrine tumors (two insulinomas, one vipoma, and two unclassified neuroendocrine tumors) were successfully visualized with Tc-99m (V) DMSA scintigraphy, thus giving an overall "imaging confirmation" of the histologic and/or cytologic results in terms of primary and metastatic localization. The authors point out the importance of their results, obtained in a simple and repeatable manner, and suggest a real comparison in this setting between this approach and octreotide scintigraphy.

High sensitivity of the in vivo detection of somatostatin receptors by 111indium (DTPA-octreotide)-scintigraphy in meningioma patients

The recent availability of isotope-labelled somatostatin analogues has allowed one to detect somatostatin receptors in normal tissue as well as in endocrine or non-endocrine cranial tumours. The purpose of the present study was to establish the value of somatostatin receptor scintigraphy using an 111Indium-labelled somatostatin analogue, octreotide, in the diagnostic work-up of meningioma patients. Twenty-two patients (16 women, 6 men, aged from 19-70 years) with newly diagnosed, residual or recurrent cranial meningiomas were examined. 111Indium-labelled DTPA-octreotide was injected i.v.. Planar and tomographic images were obtained with a gamma camera 4-6, and 24 hours after injection. In all of the meningiomas studied a high density of somatostatin receptors was detected by scintigraphy. No false negative test result was found. Due to this, a 100% predictive value of a negative test was calculated. However, when the tumours were taken in culture differing staining intensity could be seen in the light- and electron microscopic level even on individual cells of a single culture when silver intensified somatostatin-gold was used as ligand. We conclude, that in vivo somatostatin receptor scintigraphy may aid in the pre-operative differential diagnosis of skull base tumours.

Somatostatin receptor scintigraphy with [111In-DTPA-D-Phe1]- and [123I-Tyr3]-octreotide: the Rotterdam experience with more than 1000 patients

Various tumours, classically specified as either neuroendocrine or non-neuroendocrine, contain high numbers of somatostatin receptors, which enable in vivo localization of the primary tumour and its metastases by scintigraphy with the radiolabelled somatostatin analogue octreotide. In addition granulomas and autoimmune processes can be visualized because of local accumulation of somatostatin receptor-positive activated mononuclear leucocytes. In many instances a positive scintigram predicts a favourable response to treatment with octreotide. It is tempting to speculate that octreotide labelled with an appropriate radionuclide might be used in cancer therapy. The successful application of radiolabelled octreotide in scintigraphy indicates the possible usefulness of other radiolabelled peptides, either native peptides or derivatives of these, in, for example, nuclear oncology. The small size of these peptides, e.g. bombesin and substance P, is of the utmost importance for a relatively fast blood clearance, thus leading to low background radioactivity. In this way peptides are powerful alternatives to (fragments of) monoclonal antibodies, the application of which to scintigraphic localization of specific cell surface antigen-bearing tumours is plagued by slow blood clearance and, hence, high background levels.