Somatostatin-receptor imaging of human malignancies: a new era in the localization, staging, and treatment of tumors

The role of 68Ga-DOTA-NOC PET/CT in evaluating neuroendocrine tumors: real-world experience from two large neuroendocrine tumor centers

OBJECTIVE

Our aim was to assess the role of Ga-DOTA-NOC PET/CT as a tool for the management of neuroendocrine tumors (NETs), evaluating the clinical impact on patients from two large NET centers in different geopolitical settings.

PATIENTS AND METHODS

This is a retrospective study of patients with NETs who underwent Ga-DOTA-NOC PET/CT at Royal Liverpool University Hospital (UK) and at Mount Lebanon Hospital (Lebanon). Indications for imaging and findings of the PET/CT along with demographic and clinical outcome data were recorded and evaluated.

RESULTS

Four hundred and forty-five patients fulfilled the inclusion criteria, with a median age at the time of diagnosis of 56 (range: 3-90) years; 248 (55.7%) patients were male.Ga-DOTA-NOC PET/CT was indicated for staging in 193 (43.4%) patients, for diagnosis in 124 (27.9%) patients, for follow-up in 97 (21.7%) patients, and for identification of a primary NET site in 31 (7%) patients.One hundred and four (27.9%) patients underwent Ga-DOTA-NOC PET/CT for the primary diagnosis of NET, of whom 66 (52.7%) patients presented with a clinical suspicion of NET, 10 (8.3%) patients presented with a biochemical suspicion of NET only, and 48 (38.8%) patients presented with a suspicious NET lesion discovered on another imaging modality. The most common clinical presentation was typical carcinoid syndrome [4 (33%) patients].Results on the basis of histology were used as the gold standard for the diagnosis in 57% of patients and the remaining on the basis of follow-up as per established clinical consensus. Sensitivity, specificity, negative-predictive value, and positive-predictive value of PET/CT were 87.1, 97.7, 79.6, and 98.7%, respectively, for the entire sample. Accuracy was measured using the receiver operating characteristic curve analysis with an area under the curve of 0.924 (95% confidence interval: 0.874-0.974).

CONCLUSION

Ga-DOTA-NOC PET/CT is a highly sensitive and specific study for the diagnosis and follow-up of patients with neuroendocrine tumors. These results support the use of Ga-DOTA-NOC PET/CT contributing significantly toward the clinical management of NET patients.

Diagnostic performance of somatostatin receptor PET/CT using 68Ga-DOTANOC in gastrinoma patients with negative or equivocal CT findings

PURPOSE

Contrast-enhanced CT (CECT) is a standard investigative procedure in the localization of gastrinomas. Small tumors are often missed and metastatic lesions may remain occult on CT. The purpose of present study was to prospectively evaluate the diagnostic performance of (68)Ga-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI(3)-Octreotide ((68)Ga-DOTANOC) positron emission tomography/computed tomography (PET/CT) in gastrinoma patients with negative or equivocal CT findings.

METHODS

Twenty-five patients (age 46.6 ± 13.3 years; male 60%) with clinical/biochemical diagnosis of gastrinoma and negative or equivocal findings on CECT were prospectively evaluated. All of them underwent (68)Ga-DOTANOC PET/CT which was evaluated by two nuclear medicine physicians in consensus. Combination of histopathology, serum gastrin, endoscopy, and follow-up imaging were taken as reference standard.

RESULTS

(68)Ga-DOTANOC PET/CT was positive in 17 patients and negative in 8 patients, yielding an overall detection rate of 68%. It was positive 13/20 patients who underwent baseline evaluation and in 4/5 post-treatment patients. Of the 11 patients who had a negative CT result, (68)Ga-DOTANOC PET/CT was positive in four cases (detection rate 36.4%), while it was abnormal in 13/14 patients who had equivocal CT findings (detection rate 92.8%). Diagnostic performance of (68)Ga-DOTANOC PET/CT was superior in patients with equivocal CECT findings than that in patients with negative CECT (P = 0.010).

CONCLUSION

(68)Ga-DOTANOC PET/CT appears to be useful in patients with gastrinoma with negative or equivocal results on CECT, especially the latter group.

Scintigraphic imaging of body neuroendocrine tumors

Radionuclide imaging is often used in the diagnosis and work-up of a wide range of neoplasms, on the basis of the biologic behavior of the tumor. Neuroendocrine tumors are a subgroup of neoplasms that are generally small and slow growing, and consequently their identification with conventional anatomic imaging can be difficult. Depending on the physiologic properties of the tumor, functional images obtained with radionuclides are often complementary to anatomic images, not only in the localization of the tumor and its metastases, but also in the assessment of prognosis and response to therapy. Familiarity with the choice of the appropriate radiopharmaceutical, proper imaging protocols, and the wide range of imaging patterns will enable the radiologist to guide the clinician in case management.

In-111 DTPA Octreotide Scintigraphy and Intraoperative Gamma Probe Detection in the Diagnosis and Treatment of Residual Lymph Node Metastases of a Rectal Carcinoid Tumor

PURPOSE

We report a case of a rectal carcinoid tumor that was treated using endoscopic resection. This case highlights the usefulness of using somatostatin receptor scintigraphy in the postresection endoscopy of the tumor and the intraoperative use of a gamma probe detector for the surgical resection of metastatic adenopathy that had not been detected using computed tomography (CT) scanning.

METHODS

The patient was studied using CT scanning, somatostatin receptor scintigraphy (SRS), and rectal endoscopic ultrasonography (EUS). A gamma probe detector was scheduled for use during the subsequent surgical intervention.

RESULTS

The SRS demonstrated a pelvic metastatic lymphatic node that had not been detected on CT scanning. Additional EUS did not show regional metastatic lymph nodes. Histopathology following removal of retroperitoneal and presacral lymphatic nodes confirmed the diagnosis of metastatic carcinoid tumor. At follow up at 6 months, SRS and rectoscopy were normal.

CONCLUSION

Somatostatin receptor scintigraphy is very useful in identifying the presence of lymph node metastases, even with a small rectal carcinoid tumor. This is of considerable importance when scheduling surgery and the CT and EUS are normal. The use of an intraoperative gamma-probe detector assists in the surgical excision of the metastatic lymphatic nodes, especially because they had been detected only using SRS, and when their exact location is uncertain.

[Somatostatin receptor scintigraphy. When would a SPECT study be performed?]

Somatostatin receptor scintigraphy has become an essential tool in the treatment planning of patients with carcinoid tumor (CaT) and pancreatic neuroendocrine tumors (PNET). However, the contribution of SPECT images in the diagnosis and staging of these tumors has not been well established.

OBJECTIVE

1) To find out if SPECT improves the sensitivity of planar imaging and adds any value to tumor diagnosis, and 2) To determine under which circumstances SPECT images must be obtained.

MATERIAL AND METHODS

We have evaluated 49 patients, 26 females and 23 males, using both planar and SPECT 111In-DTPAOC images. The patients were classified into three groups according to their clinical indication: Group A: Indolent symptoms of CaT or PNET (n = 9); Group B: Known or functioning CaT or PNET tumors (n = 22); Group C: Post-surgical follow-up (n = 18). The total number of SPECT studies were 51 (37 abdomen, 13 thorax and 1 brain). In all cases SPECT was performed 24 hours after 111In-DTPAOC injection. Scintigraphic images were compared with surgical findings in 17 patients and with a synthesis of biochemical, clinical and CT findings in the other patients.

RESULTS

16 primary lesions were detected with planar images whereas SPECT detected 18. The two tumors detected only by SPECT were a bronchial CaT and an insulinoma located in the pancreatic tail. Planar and SPECT image sensitivities were 66.6% and 75% respectively. Twenty one patients developed metastatic disease. Sensitivities of planar and SPECT images for metastases were 76.1% and 90.4% respectively. Furthermore, SPECT helps planar images in the evaluation of six patients with uncertain images (lesions with low receptor density or with an uncertain scintigraphic localization). Therefore, in 15.6% of patients with primary or metastatic tumors, planar images were normal whereas SPECT was abnormal and SPECT provided an added value in 21.8% of the studies with abnormal planar images.

CONCLUSIONS

We recommend the use of SPECT images in: 1) Patients with specific functional clinical syndrome or with a known CaT or PNET and normal planar images. 2) When planar images are abnormal only in primary tumor. 3) In order to confirm the absence of other metastases in patients with known liver metastases. 4) In order to enhance the detection of lesions with low receptor density and uncertain planar images and 5) In order to determine exactly the anatomic location of some lesions

Radiolabeled peptides in the diagnosis and therapy of oncological diseases

There has been an exponential growth in the development of radiolabeled peptides for diagnostic and therapeutic applications in oncology. Peptides have fast clearance, rapid tissue penetration, low antigenicity and can be produced easily and inexpensively. However, peptides have problems with in vivo catabolism, unwanted physiological effects, and chelate attachment. The approved 111In-DTPA-OctreoScan, a somatostatin receptor binder, is well established for diagnosis of neuroendocrine tumors. NeoTect, an approved, 99mTc-labeled, somatostatin-receptor-binding analogue has good specificity for lung cancer detection. The receptors for Vasoactive Intestinal Peptide, Cholecystokinin-B/gastrin, Bombesin, Epidermal Growth Factor, and Alpha Melanocyte Stimulating Hormone and the Integrin, alpha(v)beta(3), are under active investigation as targets. Octreotide and its analogues labeled with 111In, 90Y, 64Cu or 177Lu are under study for the treatment of patients with promising results.

Radiolabeled peptides in diagnosis and therapy

During the past few years, there has been exponential growth in the development of radiolabeled peptides for diagnosis and therapy. This is because the peptides can be synthesized easily and inexpensively, they have fast clearance and rapid tissue penetration, and they are less likely to be immunogenic. More importantly, most peptides have a high affinity for characteristic receptor molecules that are overexpressed on malignant mammalian cells. Peptides can be labeled with a variety of radionuclides intended for specific applications, diagnostic or therapeutic, by using both conventional and novel chelating moieties, many of which can be incorporated during the solid state synthesis of a chosen peptide. High specific-activity peptides can be prepared and used to minimize unwanted physiologic effects, and known sequences of amino acids can be modified to slow their in vivo catabolic rate. These characteristics have paved the way for the preparation of a large number of radiolabeled peptides for a variety of clinical and experimental applications. This article briefly discusses the peptide chemistry; it also summarizes the preparation of radiolabeled peptides and outlines their applications in imaging vascular thrombosis, detecting infection and inflammation, and localizing tumors. Their therapeutic applications in oncology are also presented and the future directions outlined. Peptides that have been approved for human use, such as AcuTect (Diatide, Londonderry, NH) or OctreoScan (Mallinckrodt, St. Louis, MO), or those that have made it to clinical trials, are emphasized. Also discussed are selected promising agents that are still in preclinical investigation.

Somatostatin receptor scintigraphy: the definitive technique for characterizing vasoactive intestinal peptide-secreting tumors

Vasoactive intestinal peptide-secreting tumors (VIPomas) are extremely rare and difficult to diagnose. The authors describe a patient who was found to have a VIPoma after 3 years of symptoms. Somatostatin receptor scintigraphy using indium-labeled octreotide localized her tumor and prompted a surgical resection. This is the preferred imaging study for the earliest, most accurate, and cost-effective identification of VIPomas and their metastases.

Endoscopic ultrasound is highly accurate and directs management in patients with neuroendocrine tumors of the pancreas

Preoperative localization of pancreatic neuroendocrine tumors with traditional imaging fails in 40-60% of patients. Endoscopic ultrasound (EUS) is highly sensitive in the detection of these tumors. Previous reports included relatively few patients or required the collaboration of multiple centers. We report the results of EUS evaluation of 82 patients with pancreatic neuroendocrine tumors.

METHODS

We prospectively used EUS early in the diagnostic evaluation of patients with biochemical or clinical evidence of neuroendocrine tumors. Patients had surgical confirmation of tumor localization or clinical follow-up of >1 yr.

RESULTS

Eighty-two patients underwent 91 examinations (cases). Thirty patients had multiple endocrine neoplasia syndrome type 1. One hundred pancreatic tumors were visualized by EUS in 54 different patients. The remaining 28 patients had no pancreatic tumor or an extrapancreatic tumor. Surgical/pathological confirmation was obtained in 75 patients. The mean tumor diameter was 1.51 cm and 71% of the tumors were < or =2.0 cm in diameter. Of the 54 explorations with surgical confirmation of a pancreatic tumor, EUS correctly localized the tumor in 50 patients (93%). Twenty-nine insulinomas, 18 gastrinomas, as well as one glucagonoma, one carcinoid tumor, and one somatostatinoma were localized. The most common site for tumor localization was the pancreatic head (46 patients). Most tumors were hypoechoic, homogenous, and had distinct margins. EUS of the pancreas was correctly negative in 20 of 21 patients (specificity, 95%). EUS was more accurate than angiography with or without stimulation testing (secretin for gastrinoma, calcium for insulinoma), transcutaneous ultrasound, and CT in those patients undergoing further imaging procedures. EUS was not reliable in localizing extrapancreatic tumors.

CONCLUSIONS

In this series, the largest single center experience reported to date, EUS had an overall sensitivity and accuracy of 93% for pancreatic neuroendocrine tumors. Our results support the use of EUS as a primary diagnostic modality in the evaluation and management of patients with neuroendocrine tumors of the pancreas.

Synthesis and biological evaluation of Tc-99m-cyclopentadienyltricarbonyltechnetium-labeled octreotide

Octreotide was labeled at its N-terminus with Tc-99m-cyclopentadienyltricarbonyltechnetium, and the biodistribution of the labeled conjugate was studied in adult female Sprague-Dawley rats. The synthesis began with the preparation of Tc-99m-(methoxycarbonylcyclopentadienyl) tricarbonyltechnetium from Tc-99m-pertechnetate using a novel double ligand transfer reaction; it was completed in a total of five steps, with an 8% overall radiochemical yield (15% decay-corrected). The 99mTc-cyclopentadienyltricarbonyltechnetium-labeled octreotide conjugate (99mTc-CpTT-octreotide) showed receptor-mediated uptake in the pancreas and adrenals, which was blocked (80% and 93%, respectively) by excess unlabeled octreotide. These studies illustrate a new method for labeling a peptide with Tc-99m through an organometallic linkage that is stable, nonpolar, and low molecular weight; it complements labeling approaches that utilize inorganic metal complexes.

Use of somatostatin receptor scintigraphy to image extrahepatic metastases of neuroendocrine tumors

BACKGROUND

The presence of lymph node metastases significantly influences the modality of treatment in patients with liver metastases of neuroendocrine tumors (NET). Somatostatin receptor scintigraphy (Octreo-Scan, Mallinckrodt-Diagnostica, Petten, the Netherlands) is a method for localization and staging NET. The aim of our prospective study was to evaluate the effectiveness of somatostatin receptor scintigraphy in the identification of extrahepatic tumor spread.

METHODS

Thirty-five patients with liver metastases of NET were studied over a 5-year period. The presence of NET was confirmed histologically in all cases. To detect extrahepatic metastases or local tumor recurrence, conventional imaging techniques and somatostatin receptor scintigraphy were carried out.

RESULTS

In correlation with the findings of conventional imaging methods, somatostatin receptor scintigraphy confirmed liver metastases in all patients. Additionally, 19 of 35 patients (54.2%) had extrahepatic tumor lesions not detected by other imaging techniques. Of those, 15 had extensive abdominal or thoracic lymph node metastases, 3 patients had bone metastases, and in 1 patient with bronchial carcinoid local tumor recurrence was detected. All 19 patients were excluded from further evaluation for liver resection or transplantation and subjected to conservative treatment. The somatostatin receptor scintigraphy sensitivity, confirmed at the time of operation, was 91.6%. In 1 patient, in whom cluster transplantation was performed, somatostatin receptor scintigraphy failed to disclose disseminated carcinosis of the pleural cavity, detected at autopsy (false-negative rate 8.3%).

CONCLUSION

In our experience, somatostatin receptor scintigraphy provides a highly sensitive diagnostic method to localize metastases of NET. We recommend somatostatin receptor scintigraphy before liver surgery in every patient with hepatic metastases of NET to identify candidates suitable for resection.

Octreotide scanning for carcinoid tumours

The somatostatin analogue octreotide may be used in the diagnosis of carcinoid and other neuroendocrine tumours. Radionuclide scanning following intravenous injection of 111Indium-labelled octreotide (111In-DTPA-pentetreotide) provides a sensitive, non-invasive method of localising somatostatin-positive tumours. The technique may also be used to identify patients who may respond to 'cold' octreotide therapy and to monitor therapeutic efficacy.

Somatostatin receptor regulation of gastric enterochromaffin-like cell transformation to gastric carcinoid

BACKGROUND

Although somatostatin is recognized as an inhibitor of neuroendocrine cell secretion, its effect on cell proliferation has not been well defined. Generation of low acid and hypergastrinemia through irreversible H2-receptor blockade (loxtidine) in the African rodent mastomys results in gastric carcinoids (ECLomas) within 4 months. This study was undertaken to evaluate and characterize the precise somatostatin receptor (SSTR) subtype on the mastomys enterochromaffin-like (ECL) cell and to define its role in the regulation of ECL cell secretion and proliferation.

METHODS

A pure preparation (approximately 90%) of ECL cells was derived by a combination of pronase digestion and density gradient separation. We assessed the effect of somatostatin (10(-15) to 10(-7) mol/L) on gastrin-stimulated ECL cell histamine secretion and DNA synthesis (bromodeoxyuridine uptake). SSTR2 subtype was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) using gene specific primers and mRNA isolated from normal and hypergastrinemia-induced ECLoma. The polymerase chain reaction product was confirmed by Southern analysis, subcloned, and sequenced.

RESULTS

Somatostatin inhibited both gastrin-stimulated histamine secretion (IC50, 5 x 10(-13) mol/L) and DNA synthesis (IC50, 10(-10) mol/L). SSTR2 was identified in the mastomys' brain, and both normal and tumor ECL cells and comparison of the brain and ECL cell SSTR2 nucleotide sequences revealed homology of 99%.

CONCLUSIONS

The SSTR2 is expressed by the mastomys' ECL cell and ECLoma. Receptor activation inhibits both ECL cell secretory and proliferative functions.

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.

Gastrointestinal hormone mRNA expression in human colonic adenocarcinomas, hepatic metastases and cell lines

Aims-(1) To investigate the expression of the four main hormones of the digestive tract by performing reverse transcription polymerase chain reaction (RT-PCR) on a series of samples, comprising tumoral and healthy colonic tissues, hepatic metastases and colonic cell line samples; and (2) to study the patterns of labelling obtained with serological and morphological markers.Methods-After extraction and reverse transcription, gastrin, somatostatin, cholecystokinin (CCK) and transforming growth factor alpha (TGFalpha) mRNAs were detected by PCR and nested PCR using specific primers. The corresponding proteins were detected by immunohistochemistry.Results-The cell lines expressed all four mRNAs. Gastrin mRNA was present in most tumoral and metastatic samples, while the somatostatin transcript was detected in all samples and was frequently overexpressed in the normal colon. TGFalpha mRNA was expressed systematically in tumours of the right and transverse colon, but not in those located in the left colon; the expression of CCK mRNA was systematically absent in the left colon.Conclusions-The data presented here shed some light on the transcriptional events involved in the production of the various hormones present in the gastrointestinal tract, in both healthy and tumoral tissues. The various mRNAs expressed in cell lines are therefore not systematically expressed in the human pathology.

Somatostatin receptor imaging of neuroendocrine tumors with indium-111 pentetreotide (Octreoscan)

Somatostatin, a naturally occurring 14-amino acid peptide, can be thought of as an anti-growth hormone and functional down-regulator of sensitive tissue. Most neuroendocrine tumors seem to possess somatostatin receptors in sufficient abundance to allow successful scintigraphic imaging with radiolabeled somatostatin congeners. Several of these, including Indium-III-DTPA Pentetreotide (Octreoscan [Mallinckrodt Medical, St. Louis, MO]), which was approved for clinical use by the Food and Drug Administration in June 1994, have been of considerable value in scintigraphically identifying various neuroendocrine tumors. The Octreoscan compares favorably with other imaging modalities. The success of somatostatin receptor imaging in evaluating patients with suspected neuroendocrine tumors, including identifying otherwise radiographically occult lesions, has resulted in ranking somatostatin receptor imaging as the prime imaging procedure in patients with suspected neuroendocrine tumors at The Ohio State University.

Detection of somatostatin receptor subtype 2 (SSTR2) in established tumors and tumor cell lines: evidence for SSTR2 heterogeneity

The somatostatin receptor subtype 2 (SSTR2) was detected in a wide range of human and rat tumors using in vitro receptor binding ([125I]MK-678), receptor gene expression analysis, and immunoblotting techniques. The highest receptor concentrations were observed in the rat AR42J pancreatic and human small cell lung cancer (SCLC) cell lines, NCI-H69 and NCI-H345, with much lower levels detected in breast, prostate, melanoma, and hepatic tumors. Several human pancreas tumors were devoid of SSTR2. For all tumors showing detectable [125I]MK-678 binding, SSTR2 receptor mRNA was expressed. Furthermore, a mRNA transcript corresponding to a truncated isoform of SSTR2 was detected at low levels in the human SCLC NCI-H69 cell line, and likely represents a human homologue of rodent SSTR2B. Immunoblotting analysis using the SSTR2-specific antibody, 2e3, detected multiple immunoreactive protein species, including a predominant 150-kDa molecule, which could be blocked by the SSTR2-derived 2e3 peptide. Somatostatin (SRIF) peptides with high SSTR2 affinity and antiproliferative properties were potent inhibitors of [125I]MK-678 binding to several tumor types, suggesting that they may exert antitumor effects via the SSTR2 receptor.