Intraoperative detection of somatostatin-receptor-positive neuroendocrine tumours using indium-111-labelled DTPA-D-Phe1-octreotide

Radioguided Surgery for Gastroenteropancreatic Neuroendocrine Tumours: a Systematic Literature Review

BACKGROUND

Radioguided surgery (RGS) for gastroenteropancreatic neuroendocrine tumours (GEP-NETs) has been suggested as a way to improve intraoperative lesion detection. This systematic literature review of reports of the use of RGS for GEP-NETs was performed to determine if there is a benefit.

METHODS

A literature search was conducted using Google Scholar and PubMed, and snowballing from any relevant literature. Full-text studies were included if they were published in the English language and reported outcomes of RGS on human subjects with GEP-NETs. Qualitative data synthesis was performed.

RESULTS

Twenty-six papers including a total of 209 patients were included. The tracers used were predominantly indium-111 pentetreotide, gallium-68 DOTA-peptides, and technetium-99m EDDA/HYNIC-peptides. Heterogeneous protocols make comparisons difficult, but most papers reported a benefit from the use of RGS in tumours in the gastrointestinal tract; utility in localisation of pancreatic tumours was less clear. Time between tracer administration and operation varied: from 16 h to 8 days with indium-111, 0-24 h with technetium-99m, and 19-193 min with gallium-68. Eight teams reported the thresholding technique used for discrimination-four used a ratio, four statistical methods, and one looked at the sensitivity and specificity of different cut-offs. Six teams performed follow-up of 24 patients (three pancreas, eight gastrinoma, 13 gastrointestinal tract) for between 3 months and 3 years. Two patients relapsed (one pancreas, one gastrinoma) between 6 and 12 months post-surgery.

CONCLUSIONS

RGS appears to aid in localisation of gastrointestinal NETs, but the benefit is more equivocal in pancreatic NETs. Further work into outcomes is warranted.

Local treatment of liver metastases by administration of 177Lu-octreotate via isolated hepatic perfusion - A preclinical simulation of a novel treatment strategy

INTRODUCTION

Systemic ¹⁷⁷Lu-octreotate treatment for metastatic neuroendocrine tumours is restricted by organs at risk. By administering ¹⁷⁷Lu-octreotate during isolated hepatic perfusion (IHP), the uptake in organs at risk might be strongly reduced. The aim of this study was to investigate the feasibility to use the combination of IHP and radionuclide therapy.

METHODS

To simulate IHP, the liver of a pig was prepared for ex vivo perfusion. Blood containing 490 MBq ¹⁷⁷Lu-octreotate was circulated through the liver for 60 min, after which the liver was rinsed. After IHP, the liver was examined by SPECT/CT. Lastly, an intraoperative gamma detector (IGD) was used to determine ¹⁷⁷Lu activity concentration in the liver and results were compared with the activity concentration in corresponding liver biopsies.

RESULTS

Detector measurements over the liver during the IHP showed a fast increase with a maximum after approximately 10-15 min. After IHP, about 75% of the ¹⁷⁷Lu in the liver could be washed out. The SPECT/CT images revealed a relatively inhomogeneous distribution. Nevertheless, the IGD values of ¹⁷⁷Lu activity concentration showed acceptable agreement with the biopsy values.

CONCLUSIONS

Our results in pig show that it could be feasible to treat patients with liver metastases from NETs with ¹⁷⁷Lu-octreotate via IHP ¹⁷⁷. However, an inhomogeneous distribution of ¹⁷⁷Lu-octreotate in normal liver tissue is expected, and in order to determine the activity concentration with satisfactory accuracy using an IGD, measurements need to be performed at several positions over the liver.

Evaluation of two intraoperative gamma detectors for assessment of 177Lu activity concentration in vivo

BACKGROUND

Patients with somatostatin receptor-expressing neuroendocrine tumours can be treated with intravenously administered ¹⁷⁷Lu-octreotate. Few patients are cured with the present protocol due to the current dose limitation of normal organs at risk, such as the kidneys. By locally administering ¹⁷⁷Lu-octreotate to the liver for the purpose of treating liver metastases, a substantially reduced absorbed dose to organs at risk could be achieved. The development of such a technique requires the capability of measuring the ¹⁷⁷Lu activity concentration in tissues in vivo. The aim of this study was to evaluate different performance parameters of two commercially available intraoperative gamma detectors in order to investigate whether intraoperative gamma detector measurements could be used to determine ¹⁷⁷Lu activity concentration in vivo.

RESULTS

Measurements were made using different sources containing ¹⁷⁷Lu. Response linearity, sensitivity, spatial resolution and its depth dependence, organ thickness dependence of the measured count rate and tumour detectability were assessed for two intraoperative gamma detectors. The two detectors (a scintillation and a semiconductor detector) showed differences in technical performance. For example, the sensitivity was higher for the scintillation detector, while the spatial resolution was better for the semiconductor detector. Regarding organ thickness dependence and tumour detectability, similar results were obtained for both detectors, and even relatively small simulated tumours of low tumour-to-background activity concentration ratios could be detected.

CONCLUSIONS

Acceptable results were obtained for both detectors, although the semiconductor detector proved more advantageous for our purpose. The measurements demonstrated factors that must be corrected for, such as organ thickness or dead-time effects. Altogether, intraoperative gamma detector measurements could be used to determine ¹⁷⁷Lu activity concentration in vivo.

Radioguided exploration facilitates surgical cytoreduction of neuroendocrine tumors

INTRODUCTION

Radioguided exploration (RGS) can be an important tool to direct the cytoreduction of neuroendocrine tumors (NETs). The selection of the proper radiolabeled isotope, the dose, and the time interval between isotope injection and exploration are the major factors that lead to the successful use of this technique.

METHODS

Data on 43 patients who underwent RGS of their NET at our facility (Ochsner Medical Center-Kenner) was collected. These cases were reviewed to determine the optimal radiopharmaceutical, dose, and interval between injection and exploration.

RESULTS

The isotopes used were (99)technetium sulfur colloid in three patients, (123)I metaiodobenzylguanidine ((123)I-MIBG) in six patients, and (111)In-pentreotide in 30 abdominal NET patients and in four patients undergoing neck and mediastinum explorations. In 29 of 30 (111)In-pentreotide-guided abdominal explorations (five of which were re-explorations, all successful), the gamma detector was determined to be "helpful". In the four neck and mediastinum explorations, the gamma probe was deemed "essential" for completing a quick, safe, and minimally invasive procedure. (123)I-MIBG injection, in contrast, was useful in only one patient. The optimal dose and interval between injection and exploration of (111)In-pentreotide were discovered to be 6 mCi injected 7 days prior to the planned exploration.

CONCLUSION

Radioguided exploration is a useful tool to guide the cytoreduction of NETs. The correct choice of radiopharmaceutical, its dose, and the interval between injection and exploration are critical for obtaining optimal results.

Carcinoid syndrome and perioperative anesthetic considerations

Carcinoid tumors are uncommon, slow-growing neoplasms. These tumors are capable of secreting numerous bioactive substances, which results in significant potential challenges in the management of patients afflicted with carcinoid syndrome. Over the past two decades, both surgical and medical therapeutic options have broadened, resulting in improved outcomes. The pathophysiology, clinical signs and symptoms, diagnosis, treatment options, and perioperative management, including anesthetic considerations, of carcinoid syndrome are presented.

Long-term survival of patients with small intestinal carcinoid tumors

Midgut carcinoid tumors are rare and have a markedly better prognosis than adenocarcinoma in the small intestine. New diagnostic methods and medical as well as surgical therapies have evolved during the last decades, leading to more active care of these patients. Patients with small intestinal carcinoids diagnosed from 1960 to 2000 in the duodenum (n = 89) and jejunum/ileum (n = 2437) were identified in the Swedish Cancer Registry. Cases without histologic verification and autopsy cases were excluded. Overall, cause-specific and relative survival were calculated. The overall 5-, 10-, and 15 year survivals were, respectively, 60%, 46%, and 28% for duodenal tumors and 56%, 36%, and 23% for jejunal/ileal tumors. Cause-specific 5-, 10-, and 15-year survival was 94% for all three follow-up periods for duodenal tumors and 87%, 80%, and 77% for those in the jejunum/ileum. The corresponding relative survivals were, respectively, 72%, 67%, and 51% for duodenal tumors and 67%, 54%, and 44% for those in the jejunum/ileum. Sex did not influence overall or cause-specific survival. The age at diagnosis correlated inversely with overall and cause-specific survival for tumors in the jejunum/ileum. For tumors in the jejunum/ileum, the overall and cause-specific survival correlated with the time period of diagnosis, with a more favorable prognosis for those diagnosed in recent years. A multivariate Cox proportional hazards model showed similar results. We concluded that young age and diagnosis in recent years are positive predictors of survival for patients with midgut carcinoids. The divergence between cause-specific and relative survival implies the need for a more detailed analysis of the causes of death of these patients.

Intraoperative gamma probe detection of lymph node recurrence of insulinoma

Insulinomas are rare endocrine tumors that are mostly sporadic, benign, and small. Preoperative radiography diagnosis may be difficult. Intraoperative palpation and ultrasound remain the gold standard for detection and planned resection. Recent studies find intraoperative gamma-probe localization as a good technique for identifying primary neuroendocrine tumors. We report a case of a 75-year-old woman with functioning lymph node recurrence of a malignant insulinoma. Spleno-pancreatectomy was performed in order to treat the malignant insulinoma. Clinical, biochemical, and radiological examination confirmed the total excision of the primary lesion. However, clinical symptoms appeared 9 months later. Octreo-scan, abdominal CT, and biochemical study showed lymph node recurrence and four hepatic metastases. Surgery was performed after two [111In-DTPA] octreotide scans. Intraoperative gamma probe detection was planned in order to localize a small latero-aortic lymph node recurrence. Intraoperative count rates were high in para-aortic tissue. Para-aortic lymphadenectomy and metastasectomy were carried out. Ex-situ count rates and histological examination confirmed the recurrence. Six months later clinical and biochemical studies and scans remain negative for recurrence. Intraoperative [111In-DTPA] octreotide gamma probe examination may be a useful tool in the surgical approach to insulinoma recurrence.

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.

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

111In-labelled octreotide binding by the somatostatin receptor subtype 2 in neuroendocrine tumours

BACKGROUND

The aim of this study was to investigate the importance of somatostatin receptor subtype 2 (SSTR2) expression for 111In-labelled diethylenetriamine-pentaacetic acid (DTPA)-D-Phe1-octreotide binding and uptake of 111In in neuroendocrine tumours.

METHODS

111In activity concentrations in surgical biopsies from neuroendocrine tumours (midgut carcinoid and medullary thyroid carcinoma), breast carcinoma and blood were determined 1-8 days after intravenous injection of 111In-labelled DTPA-D-Phe1-octreotide (140-350 MBq). The ratio of 111In activity concentrations between tumour tissue and blood (T/B value) was calculated. The expression of SSTR2 messenger RNA (mRNA) in tumour biopsies was quantitated by ribonuclease protection assay and SSTR2 protein was localized by immunocytochemistry.

RESULTS

T/B values were highest for tumour biopsies from midgut carcinoids (mean 160 (range 4-1200); n = 65) followed by medullary thyroid carcinoma (mean 38 (range 2-350); n = 88) and breast carcinoma (mean 18 (range 4-41); n = 4). The expression of SSTR2 mRNA (relative to the NCI-H69 cell line) was highest in tumour biopsies from midgut carcinoids (mean 2.5 (range 0.83-6.0); n = 40) followed by medullary thyroid carcinoma (mean 1.3 (range 0.20-6.0); n = 7) and breast carcinoma (mean 0.66 (range 0.29-1.0); n = 9). In tumour biopsies SSTR2 protein was localized exclusively to tumour cells.

CONCLUSION

Midgut carcinoid tumours showed a much higher level of SSTR2 expression than medullary thyroid carcinoma in accordance with superior tumour imaging by octreotide scintigraphy. The high SSTR2 mRNA values and T/B values observed in midgut carcinoid tumours were positively correlated.

Biodistribution of 111in-DTPA-D-Phe1-octreotide in tumor-bearing nude mice: influence of amount injected and route of administration

In nude mice carrying the human carcionoid GOT1 different amounts of (111)In-DTPA-Phe(1)-octreotide and routes of administration were studied in relation to uptake in tumor and normal organs. The relative organ uptake varied with given amount; highest in tumor after 0.1 and 1 microg and lowest in muscle, heart and blood after 0.1 microg. The uptake decreased in lungs and spleen with higher amounts of (111)In-DTPA-Phe(1)-octreotide. In all organs studied the tumor-to-normal-tissue activity concentration ratio was maximal at 0.1 and 1 microg, but route of administration influenced the uptake only little.

Somatostatin analogs in the diagnosis and treatment of cancer

Over the past few years, significant progress has been made in our understanding of the biology and functional significance of somatostatin receptors (sst) on human tumors. Somatostatin analogs, such as octreotide, bind predominantly to sst(2) and successfully control hormone hypersecretion in patients with acromegaly, islet cell tumors and carcinoids, and (temporary) control of tumor growth is often also seen. Furthermore, sst(2) on tumors can be imaged in vivo after the injection of radionuclide-coupled octreotide. Targeted chemo- and radiotherapy, in which somatostatin analogs coupled to a chemotherapeutic agent or a radionuclide are selectively internalized by sst-positive tumors, are now being studied for their effect on tumor growth. Knowledge about the differential anti-tumor effects of the sst subtypes on tumor cells might have clinical significance after the development of new subtype-specific somatostatin analogs.

Indium-111-octreotide scintigraphy, intraoperative gamma-detector localisation and somatostatin receptor expression in primary human breast cancer

12 women with primary breast cancer underwent somatostatin receptor scintigraphy (SRS) with 111In-DTPA-D-Phe1-octreotide. The tumour sizes varied between 2 and 5 cm and were all, except one, palpable at clinical examination. Tumour biopsies were taken with additional sampling from normal breast tissue, fat, muscle, axillary lymph nodes and peripheral blood. Ratios between the 111In activity concentration in the tissue biopsies (Ti) and in peripheral blood (B) as well as in normal breast tissue (Br) were calculated. In 8/12 patients the scintillation detector was used intraoperatively for radioactivity measurements of the biopsies in situ and ex vivo. The sstr-subtype profiles were determined by northern blot analysis and the relative expression of sstr2 by ribonuclease protection assay (RPA) and immunocytochemistry. Preoperative SRS visualised all primary breast cancer tumours. The scintigraphic image showed no correlation with the histopathological type of the tumour or with the abundance of oestrogen/progesterone receptors on the tumour. Two patients with a massive tumour infiltration of the lymph nodes had a distinct positive SRS of the ipsilateral axilla. In one patient with three nodal metastases the scintigraphic image of the axilla was weak but visible. Four other patients with a negative axillary scintigraphy had 1-2 lymph node metastases. The Ti/B ratios for the breast tumours varied between four and 33 and were not different from Ti/Br ratios. In lymph node metastases the Ti/B ratios were higher (10-41). Intraoperative detector measurements showed a significant difference between the breast tumour and normal tissue in 2/8 patients in situ. Similar measurements on excised tissues (ex vivo) showed a significant difference in 6/8 patients. Two patients with lymph node metastases exhibited a significantly increased uptake ex vivo by detector measurements, but in only one of them in situ. All tumour biopsies expressed the presence of sstrl, 3, 4 and 5, but not of sstr2 at northern analysis. On the other hand, sstr2 was detected in all tumours by RPA and immunocytochemistry. Preoperative SRS visualised primary breast cancer lesions in all 12 patients. SRS could also demonstrate extensive axillary tumour infiltration. Intraoperative use of the scintillation detector could not exclude axillary metastases in situ. The low Ti/B values of both primary tumours and metastases indicate limitations of the radiopharmaceutical used.

Nuclear medicine imaging of neuroendocrine tumours

Different tracers have been proposed in nuclear medicine to visualize neuroendocrine tumours: the majority are based on specific uptake mechanisms while some are aspecific. Among the most important gamma-emitting tracers, radiolabelled metaiodobenzylguanidine (123I or 121I-MIBG) and 111In-pentetreotide should be mentioned. In particular. good results can be obtained with 111In-pentetreotide scanning, which visualizes more than 70% of all neuroendocrine tumours and in some indications, as in gastro-entero-pancreatic (GEP) tumours, has a diagnostic sensitivity superior to that of conventional radiological imaging. Radiolabelled monoclonal antibodies have at present only a storical value, while a series of new peptides represent interesting subjects in areas currently being regarded. Positron emission tomography (PET) is a successful modality to detect cancer and recent years, has demonstrated a great diagnostic value in a large series of tumour types. 18F-deoxyglucose (FDG)-PET has also been used to diagnose tumours of neuroendocrine origin. Even if 18F-FDG has been successfully and widely employed in oncology, it has not demostrated a significant uptake in well differentiated neuroendocrine tissues. On the contrary, other positron emitter tracers seem to be more promising. A serotonin precursor 5-hydroxytryptophan (5-HTP) labelled with 11C has shown an increased uptake in carcinoids. This uptake seems to be selective and some clinical evidence has demonstrated that it allows the detection of more lesions with PET than with CT or octreotide scintigraphy. Another radiopharmaceutical in development for PET is 11C L-DOPA, which seems to be useful in visualizing endocrine pancreatic tumours. This Review summarizes the potential of several nuclear medicine techniques in the diagnosis of neuroendocrine tumours and stresses the renewed role of nuclear -medicine in the management of this disease.

Receptor-targeted optical imaging of tumors with near-infrared fluorescent ligands

We report here the in vivo diagnostic use of a peptide-dye conjugate consisting of a cyanine dye and the somatostatin analog octreotate as a contrast agent for optical tumor imaging. When used in whole-body in vivo imaging of mouse xenografts, indotricarbocyanine-octreotate accumulated in tumor tissue. Tumor fluorescence rapidly increased and was more than threefold higher than that of normal tissue from 3 to 24 h after application. The targeting conjugate was also specifically internalized by primary human neuroendocrine tumor cells. This imaging approach, combining the specificity of ligand/receptor interaction with near-infrared fluorescence detection, may be applied in various other fields of cancer diagnosis.

Cushing's syndrome associated with a chemodectoma and a carcinoid tumour

We present a case of Cushing's syndrome where ¹¹¹ In-octreotide scanning provided evidence for the presence of two neuroendocrine tumours. Uptake in the right neck corresponded to a chemodectoma, but there was no change in the clinical condition or fall in ACTH levels following surgical resection. Uptake in the left chest was assumed to relate to a bronchial carcinoid, but a tumour could not initially be localized on magnetic resonance imaging (MRI), spiral CT scanning or on selective venous sampling. A 1 cm bronchial carcinoid tumour was identified post-mortem which immunostained for ACTH. This case demonstrates that ¹¹¹ ln-octreotide scanning is a useful technique for identifying the source of ectopic ACTH production in difficult cases of Cushing's syndrome. Reliance should not be placed solely on standard imaging techniques to localize the tumour prior to surgery. Although rare, the possibility of a non-ACTH secreting neuroendocrine tumour should also be considered in patients with ectopic ACTH syndrome, who have positive ¹¹¹ In-octreotide scans.

Internalization of [DOTA degrees,125I-Tyr3]Octreotide by somatostatin receptor-positive cells in vitro and in vivo: implications for somatostatin receptor-targeted radio-guided surgery

We compared internalization of three radioiodinated octreotide (OCT) somatostatin (SS) analogs-[125I-Tyr3]OCT, [DTPA degrees, 125I-Tyr3]OCT, and [DOTA degrees,125I-Tyr3]OCT-by somatostatin receptor (SSR)-positive mouse AtT20 pituitary tumor cells and human insulinoma cells. The three SS analogs were internalized in a specific, time-dependent manner. Internalization was significantly inhibited by pertussis toxin (100 microg/l) by 38%, 43%, and 31%, and by an inhibitor of receptor-mediated endocytosis (phenyl arsine oxide; 10 microM) by 98%, 94%, and 92%, respectively. Binding affinities of the three radioligands were comparable (0.2, 0.2, and 0.3 nM, respectively). However, [DOTA degrees,125I-Tyr3]OCT was internalized in a five-fold higher amount in comparison with the two other radioligands. A comparably high uptake of [DOTA degrees, 125I-Tyr3]OCT was found in SSR-positive organs (pituitary, pancreas, and adrenals) in vivo in rats (a ten-fold, five-fold, and eight-fold higher uptake 4 hr post injection, respectively, compared with the two other radioligands). This resulted in very high target-background ratios for [DOTA degrees,125I-Tyr3]OCT 4 hr post injection amounting to 274, 566, and 623 in the pituitary, adrenals, and pancreas, respectively. Both in vivo and in vitro there was a rapid dissociation of radioactivity from the SSR-positive cells. Main conclusions are that: 1) coupling of chelating groups like DTPA or DOTA to the SS analog [Tyr3]OCT does not prevent the internalization of OCT after binding to SSRs; 2) [DOTA degrees, 125I-Tyr3]OCT is internalized in a significantly higher amount by AtT20 and human insulinoma cells and in vivo in rats in SSR-positive organs, in comparison with [DTPA degrees,125I-Tyr3]OCT and [125I-Tyr3]OCT; and 3) the very high target-background ratios in vivo make radioiodinated [DOTA degrees,Tyr3]OCT a very suitable ligand for SSR-targeted radioguided surgery of SSR-positive human neuroendocrine tumors.

Comparative studies on the expression of somatostatin receptor subtypes, outcome of octreotide scintigraphy and response to octreotide treatment in patients with carcinoid tumours

We have compared the expression of somatostatin receptor (sstr) subtypes with the outcome of somatostatin receptor scintigraphy and the effect of somatostatin receptor activation in patients with disseminated carcinoid tumours. Tumour tissues from nine patients with midgut carcinoids (ileal) and three patients with foregut carcinoids (gastric, thymic) were analysed using Northern blotting. Expression of somatostatin receptors was demonstrated in all tumours (12 out of 12), with all five receptor subtypes present in 9 out of 12 tumours. Somatostatin receptor scintigraphy using [111In]DTPA-D-Phe1-octreotide visualized tumours in all patients (12 out of 12). The 111In activity concentrations in tumour tissue (T) and blood (B) were determined in three tumours 1-7 days after injection of the radionuclide. The T/B 111In activity concentration ratios ranged between 32 and 651. Clinically, treatment with the long-acting somatostatin analogue octreotide resulted in marked symptom relief accompanied by a significant reduction in tumour markers, for example urinary-5-HIAA levels (28-71% reduction). Incubation of midgut carcinoid tumours in primary culture with octreotide (10 microM) resulted in a reduction in spontaneously secreted serotonin (45-71% reduction) and 5-HIAA (41-94% reduction). The results demonstrate that carcinoid tumours possess multiple somatostatin receptor subtypes and that somatostatin analogues such as octreotide, which preferentially bind to somatostatin receptor subtype 2 and 5, can be used in the diagnosis and medical treatment of these tumours. In the future, novel somatostatin analogues with subtype specific receptor profiles may prove to be of value for individualizing the treatment of disseminated carcinoid tumour disease.

The relevance of somatostatin receptors in thyroid neoplasia

111In-octreotide scintigraphy in patients with persistent medullary thyroid carcinoma (MTC) visualized tumors in about half of the surgically explored sites. Tumor visualization correlated with rapid tumor growth and large tumor volume as judged from calcitonin levels. The 111In concentration ratio between tumor (T) and blood (B) in surgically excised lymph node metastases of MTC showed a large variation, with low values for microscopic and high values for macroscopic metastases in individual patients. Three cases of MTC, Hürthle cell adenoma and papillary thyroid cancer are reported with preoperative scintigraphy, T/B ratios and Northern analyses of the surgical biopsies. Visualization of tumors was possible in the absence of sstr2 (the high affinity receptor for octreotide) with the exception of microscopic tumor growth. T/B values in the patient with Hürthle cell adenoma were similar to those found in the contralateral thyroid lobe with goitre. The relatively high uptake of 111In in benign thyroid conditions probably limits the use of octreotide scintigraphy in the diagnosis of primary tumors. The technique has certain advantages over radioiodine scintigraphy after the surgical treatment of thyroid tumors: no need for withdrawal of thyroxin substitution; a possibility to diagnose metastases of tumors that do not concentrate radioiodine (MTC, Hürthle cell cancer); and complementary information about metastatic sites of non-medullary thyroid cancer (papillary and follicular tumors).