The diagnostic utility of somatostatin receptor scintigraphy in oncology

Current Role of 111In-DTPA-Octreotide Scintigraphy in Diagnosis of Thymic Masses

Aims and background

Thymic tumors (thymomas and thymic carcinomas) represent 50% of all mediastinal tumors. Thymomas usually express high levels of somatostatin receptors, which enable in vivo imaging with 111In-DTPA-octreotide (OctreoScan®). The aim of this study was to further investigate the role of radionuclide techniques in the diagnosis, staging and follow-up of these tumors.

Methods

Eight patients (5 women, 3 men, age range 35–79 years; mean ± SD 56.1 ± 15.8 years) entered the study. In 4 patients, myasthenia gravis was the presenting symptom. 111In-DTPA-octreotide scan was performed within 3 weeks after contrast enhanced CT and/or MRI. Planar and tomographic images were acquired within 24 hours of the injection of 111 MBq OctreoScan. The scintigraphic results were defined in correlation with the histological findings.

Results

Histology revealed thymoma in 3 patients, thymic carcinoma in 1, insular carcinoma of presumably thymic origin in 1, thymic carcinoid in 1, and thymic hyperplasia in 2 patients. Two thymomas were at stage I, 1 thymoma and 1 thymic carcinoma at stage II, 1 insular carcinoma of presumably thymic origin at stage IV, and 1 thymic carcinoid at stage IV. OctreoScan consistently accumulated in primary and/or metastatic sites of thymic tumors while no radiotracer uptake was detected in the 2 patients with benign thymic hyperplasia. In 1 patient with a very large mediastinal mass (13 cm in largest diameter) and multiple metastatic deposits in the lungs, OctreoScan scintigraphy showed a large area of pathological uptake in the anterior mediastinum and a small area of focal uptake in the cervical-dorsal region of the right lung corresponding to a lymph node expressing somatostatin receptors.

Conclusions

OctreoScan is avidly taken up by thymic tumors, enabling the diagnosis of these tumors and a better evaluation of their extension. It does not accumulate in thymic hyperplasia, thus allowing the differential diagnosis between these 2 pathological conditions. In patients affected by myasthenia gravis, OctreoScan scintigraphy can play an important role in characterizing thymic masses.

99mTc-Hynic-TOC imaging in the diagnostic of neuroendocrine tumors

The aim of this study was to assess the potential of ^99mTc-Hynic-TOC imaging in the primary diagnosis and follow-up of midgut neuroendocrine tumors (NETs). In comparison to ¹¹¹In-octreotide, ^99mTc-Hynic-TOC has a higher imaging quality and leads to a lower radiation absorption in patients. ^99mTc-Hynic-TOC was used for assessing primary diagnosis (n = 14) and during follow-up (n = 17) in patients with NETs. The scintigraphic findings were compared with computed tomography scans and follow-up. In 31 patients, 34 somatostatin receptor scans using 99mTc-Hynic-TOC were performed. The primary diagnoses were midgut NET. The scintigraphy was true positive in 17 patients, true negative in 9, false negative in 4, and false positive in 1. From these data, a sensitivity of 81%, specificity of 90%, positive predictive value of 94%, and negative predictive value of 69% were calculated. In summary, ^99mTc-TOC represents a useful radiotracer in imaging SSTR-expressing tumor lesions with slightly higher sensitivity, higher imaging quality, and lower radiation exposure for patients compared to ¹¹¹In-octreotide. A 1-day double-acquisition protocol should be used to reduce false-positive findings of the gut.

The clinical impact of a combined gamma camera/CT imaging system on somatostatin receptor imaging of neuroendocrine tumours

AIM

With a combined gamma camera/CT imaging system, CT images are obtained which are inherently registered to the emission images and can be used for the attenuation correction of SPECT and for mapping the functional information from these nuclear medicine tomograms onto anatomy. The aim of this study was to evaluate the clinical impact of SPECT/CT using such a system for somatostatin receptor imaging (SRI) of neuroendocrine tumours.

MATERIALS AND METHODS

SPECT/CT imaging with (111)In-Pentetreotide was performed on 29 consecutive patients, the majority of whom had carcinoid disease. All SPECT images were first reported in isolation and then re-reported with the addition of the CT images for functional anatomical mapping (FAM).

RESULTS

Fifteen of the 29 SPECT images were reported as abnormal, and in 11 of these abnormal images (73%) FAM was found to either establish a previously unknown location (7/11) or change the location (4/11) of at least one lesion. The revised location could be independently confirmed in 64% of these cases. Confirmation of location was not possible in the other patients due to either a lack of other relevant investigations, or the fact that lesions seen in the SPECT images were not apparent in the other investigations. FAM affected patient management in 64% of the cases where the additional anatomical information caused a change in the reported location of lesions.

CONCLUSION

These results imply that FAM can improve the reporting accuracy for SPECT SRI with significant impact on patient management.

Receptor-Mediated Tumor Targeting with Radiopeptides. Part 1. General Concepts and Methods: Applications to Somatostatin Receptor-Expressing Tumors

Radiolabeled peptides have become important tools in nuclear oncology, both as diagnostics and more recently also as therapeutics. They represent a distinct sector of the molecular targeting approach, which in many areas of therapy will implement the old "magic bullet" concept by specifically directing the therapeutic agent to the site of action. In this three-part review, we present a comprehensive overview of the literature on receptor-mediated tumor targeting with the different radiopeptides currently studied. Part I summarizes the general concepts and methods of targeting, the selection of radioisotopes, chelators, and the criteria of peptide ligand development. Then, the >400 studies on the application to somatostatin/somatostatin-release inhibiting factor receptor-mediated tumor localization and treatment will be reviewed, demonstrating that peptide radiopharmaceuticals have gained an important position in clinical medicine.

[Radio-guided resection of residual metastatic lymph node from a previously resected neuroendocrine tumor]

Neuroendocrine tumors are slowly growing and carry a high risk of recurrence. Somatostatin receptor scintigraphy is considered as the gold standard for preoperative evaluation and postoperative follow-up. The use of an intraoperative detection probe makes easier a complete resection of abdominal residual or recurrent tumor. These resections may be incomplete because of the small size of the tumor and the postoperative adhesions. Radio-guided surgery is recommended in order to reduce the need for reoperation.

Somatostatin receptor imaging, therapy and new strategies in patients with neuroendocrine tumours

BACKGROUND

Somatostatin receptors have been found on a variety of neuroendocrine tumours, such as carcinoids and paragangliomas, as well as on most pancreatic endocrine and breast tumours. Somatostatin receptor scintigraphy with a radionuclide-labelled somatostatin analogue, [111Indium- diethylenetriaminopenta-acetic acid]octreotide, is a sensitive and specific technique for visualizing in vivo the presence of somatostatin receptors on various tumours.

METHODS

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature. Additional material was obtained from recently published abstracts of meetings.

RESULTS AND CONCLUSION

Somatostatin receptor imaging of neuroendocrine tumours is essential in the diagnostic evaluation of most of these tumours. The expression of somatostatin receptors in vivo not only predicts the outcome of somatostatin analogue treatment but also opens the possibility of new therapeutic strategies. Because better information about spread of the disease can be obtained, more justifiable options for therapy can be proposed.

Somatostatin receptor scintigraphy in thymoma imaging method and clinical application

Somatostatin receptor scintigraphy with 111In-[DTPA-D-Phe1]-octreotide has the potential for visualizing primary and recurrent thymomas in patients with myasthenia gravis, whereas thymic hyperplasias fail to accumulate somatostatin analog peptides. We demonstrate somatostatin receptor imaging findings in a patient with a mixed encapsulated thymoma which exhibited intense 111In-[DTPA-D-Phe1]-octreotide uptake in early and late scans. In another patient with a history of malignant thymoma 111In-[DTPA-D-Phe1]-octreotide accumulation was clearly seen in a mass suspected to be a recurrence. This paper describes the imaging protocol including Single Photon Emission Computed Tomography (SPECT) and discusses the clinical applications of this feasible functional imaging method in patients with thymomas.

Somatostatin receptor scintigraphy and somatostatin therapy in the evaluation and treatment of malignant thymoma

PURPOSE

This report illustrates the potential diagnostic and therapeutic utility of somatostatin receptor scintigraphy and therapy with somatostatin.

METHODS

In-111 pentetreotide (In-111 octreotide), a somatostatin analog, was used to define the receptor status and the extent of disease in a case of malignant thymoma.

RESULTS

Subsequent treatment with nonradioactive somatostatin inhibited tumor growth.

CONCLUSION

In-111 octreotide may be useful to define tumor receptor status and may provide prognostic information useful in determining subsequent therapy.