Use of isotope-labeled somatostatin analogs for visualization of islet cell tumors

Somatostatin analogs therapy in gastroenteropancreatic neuroendocrine tumors: current aspects and new perspectives

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare tumors that present many clinical features secreting peptides and neuroamines that cause distinct clinical syndromes such as carcinoid syndrome. However most of them are clinically silent until late presentation with mass effects. Surgical resection is the first line treatment for a patient with a GEP-NET while in metastatic disease multiple therapeutic approaches are possible. GEP-NETs are able to express somatostatin receptors (SSTRs) bounded by somatostatin (SST) or its synthetic analogs, although the subtypes and number of SSTRs expressed are very variable. In particular, SST analogs are used frequently to control hormone-related symptoms while their anti-neoplastic activity seems to result prevalently in tumor stabilization. Patients who fail to respond or cease to respond to standard SST analogs treatment seem to have a response to higher doses of these drugs. For this reason, the use of higher doses of SST analogs will probably improve the clinical management of these patients.

Somatostatin analogues in the treatment of gastroenteropancreatic neuroendocrine tumours, current aspects and new perspectives

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) are rare tumours that present many clinical features.They secrete peptides and neuroamines that cause distinct clinical syndromes, including carcinoid syndrome. However, many are clinically silent until late presentation with mass effects.In 2000 the WHO developed a new classification which gives a better description of the characteristics and biological behaviour of the tumour.Surgical resection is the treatment of first choice for a patient with a GEP NET. In metastatic disease multiple therapeutic approaches are possible. In these cases the goal is to improve quality of life and to extent survival.GEP NETs express somatostatin receptors (SSTRs), which are bound by somatostatin (SST) or its synthetic analogues, although the subtypes and number of SSTRs expressed is very variable.Somatostatin analogues are used frequently to control hormone-related symptoms while their anti-neoplastic activity, even if it has not been widely studied and the regarding data are discordant, seems to result prevalently in tumour stabilisation.A few patients who fail to respond or cease to respond to standard SST analogues treatment seem to have a response to higher doses of these drugs.The use of higher doses of somatostatin analogues or the development of new subtype selective agonists and chimaeric somatostatin analogues, or pan-somatostatin will probably improve the clinical management of these patients.This review provides an update on the use of somatostatin analogues in the management of GEP NETs and discusses novel clinical strategies based on SSTR 2 gene transfer therapy.

Insulin secretion and insulin-producing tumors

Insulinomas are rare neuroendocrine tumors of pancreatic islet cells that retain the ability to produce and secrete insulin. In contrast to normally differentiated β-cells, insulinoma cells continue to secrete insulin and proinsulin at low blood glucose. This deregulated insulin secretion manifests clinically as fasting hypoglycemia. The molecular pathways that characterize normal insulin secretion and β-cell growth are reviewed and contrasted to the biology of insulinomas. The second half of this review summarizes the clinical approach to the disorder. The diagnosis of insulinoma is established by demonstrating inappropriately high insulin levels with coincident hypoglycemia at the time of a supervised fast. Localization of insulinomas is challenging owing to their small size but should be attempted to maximize the chance for successful surgical resection and avoid risks associated with reoperation. In the majority of cases, successful surgical resection leads to lifelong cure.

The role of somatostatin analogues in the treatment of neuroendocrine tumours

Neuroendocrine tumours belong to a heterogeneous family of neoplasms, originating in endocrine glands (such as the pituitary, parathyroid or the neuroendocrine adrenal glands), in endocrine islets (within the thyroid or pancreas) as well as in endocrine cells dispersed between exocrine cells throughout the digestive or respiratory tracts. The clinical behaviour of neuroendocrine tumours is variable; they may be functioning or not functioning, ranging from well-differentiated slow growing neuroendocrine tumours to poorly differentiated neuroendocrine tumours, which are highly aggressive malignant tumours. The development of somatostatin analogues as important diagnostic and treatment tools have revolutionised the clinical management of patients with neuroendocrine tumours. However, although symptomatic relief and stabilisation of tumour growth for various periods of time are observed in many patients treated with somatostatin analogues, tumour regression is rare. Development of new somatostatin analogues and new drug combination therapies should further improve the clinical management of these patients.

Complete clinical remission and disappearance of liver metastases after treatment with somatostatin analogue in a 40-year-old woman with a malignant insulinoma positive for somatostatin receptors type 2

Insulinoma is the most common pancreatic endocrine tumor, accounting for 40% of all pancreatic functional neoplasm, and is characterized by hypersecretion of insulin and hypoglycemia. Elective treatment for insulinomas is surgical enucleation. Medical therapy with diazoxide, followed by somatostatin analogues in some cases, may be necessary to treat the hypoglycemic symptoms. We report a case of a patient affected by metastatic insulinoma with severe hypoglycemia. After surgery, histopathology confirmed the presence of a malignant insulinoma with multiple metastases in the liver. Due to the persistence of hypoglycemia, the patient was started on octreotide LAR treatment, which determined a complete clinical remission with regression of the metastatic lesions in the liver after one year. Repeated CT scans 2 and 3 years after surgery confirmed the remission. To our knowledge, the complete regression of the disease in insulinomas treated with long-standing somatostatin analogue therapy has never been reported. Immunohistochemical analysis in tissue specimens showed a strong membrane immunoreactivity for somatostatin receptors type 2 (SSTR2) in both the primary nodule and the metastases. The capacity of somatostatin analogues to negatively regulate cell proliferation through indirect and direct mechanisms has been experimentally demonstrated. Furthermore, SSTR2 activation may exert pro-apoptotic effects in neoplastic cells. Thus, both mechanisms may have been responsible of the remission of the disease in this patient. This case underlies the potential impact of the treatment of pancreatic insulinomas with somatostatin analogues, and, if confirmed, the usefulness of SSTR determination in these neoplastic specimens.

Pitfalls in the surgical treatment of insulinoma

BACKGROUND

In the 75 years since an insulinoma was first described, the challenge for the surgeon has been one of localization. The combination of endoscopic ultrasound (EUS) or intraoperative ultrasound and operative palpation has led to nearly 100% success rate at primary operation in experienced institutions. However, 13% of patients at referral centers undergo reexploration, which has an increased morbidity. With more successful localization modalities, the operative failures have become more challenging than ever.

METHODS

During the past 35 years, we have treated 118 cases of sporadic insulinoma. Technical advances in EUS have led to preoperative identification of more than 90% of insulinomas. Despite this success we have become increasingly aware of the limitations of EUS in the surgical treatment of insulinoma. We present the pitfalls of 6 recent cases.

RESULTS

The limitations of EUS include the assessment of malignancy, the identification of pedunculated or adjacent lesions, the evaluation of distal pancreatic lesions, and the differentiation of larger homogeneous tumors from surrounding parenchyma.

CONCLUSIONS

The surgical challenge in the treatment of insulinomas has transformed from one of localization to one of recognizing the limitations of our current localization modalities. By sharing our experience with recent difficult cases, we guide the surgeon to greater success and the patient to decreased morbidity.

Laparoscopic detection and resection of insulinomas

BACKGROUND

Laparoscopic ultrasonography as a diagnostic tool for the localization of islet cell tumors has been described before, but few reports on laparoscopic resection of insulinomas exist. We retrospectively reviewed the results of our experience with laparoscopic detection and the resection of insulinomas to determine its feasibility.

METHODS

Between February 1996 and February 1999, 10 patients underwent operation for organic hyperinsulinism at our institution. Patient and clinical characteristics were studied retrospectively. Laparoscopic ultrasonography was performed to localize the insulinoma and then laparoscopic resection was performed.

RESULTS

Eight women and 2 men underwent operation for hyperinsulinism. In 6 patients the insulinoma could be resected laparoscopically, either by enucleation (5 patients) or by resection of the pancreatic tail (1 patient). Four procedures were converted to laparotomy for the proximate location of the insulinoma to the portal vein or pancreatic duct (3 procedures) and failure to identify the insulinoma (1 procedure). The overall success rate of preoperative localization of an insulinoma with the use of various imaging techniques was 60% (6/10 patients). Laparoscopic ultrasonography could identify an insulinoma in 90% of the patients (9/10 patients). The median hospital stay was 7 days.

CONCLUSIONS

Laparoscopic ultrasonography followed by laparoscopic removal of the insulinoma in patients with clinically manifested hyperinsulinism is a feasible and safe technique with low morbidity and fast postoperative recovery. Preoperative localization studies appear of limited value.

The role of fluorodeoxyglucose and positron emission tomography in the evaluation of pancreatic disease

BACKGROUND

The difficulties involved in the timely and accurate diagnosis of pancreatic disease are well known. The usual imaging modalities usually identify abnormalities but may not always differentiate malignancy from other condition such as scar tissue or chronic inflammation. The purpose of our study was to determine if fluorodeoxyglucose positron emission tomography (FDG PET) can accurately diagnose pancreatic disease.

METHODS

The records of 15 patients presenting with pancreatic disease were retrospectively reviewed. The diagnosis suspected by imaging modalities was compared with the final tissue diagnosis. Two patients were excluded because no tissue was obtained.

RESULTS

Adenocarcinoma was diagnosed in 9 patients. A mass consistent with this diagnosis was seen in 8 of 9, 6 of 9, 6 of 8, and 5 of 5 patients by PET, computed tomography (CT), endoscopic retrograde cholangiopancreatography (ERCP), and endoscopic ultrasound (EUS), respectively. Chronic pancreatitis (CP) was diagnosed in 2 patients. The unique appearance on FDG PET made the diagnosis in both these patients. Both patients with CP were thought to have a malignancy by CT and EUS and 1 of 2 by ERCP. Neuroendocrine tumors were diagnosed in 2 other patients. One of 2 was seen by FDG PET and both by CT.

CONCLUSIONS

FDG PET can accurately differentiate a pancreatic adenocarcinoma from chronic pancreatitis in a patient with a suspicious pancreatic mass. Thus, FDG PET may help in establishing a diagnosis and subsequently managing a patient with pancreatic disease.

MR imaging of metastatic pancreatic VIPoma

The MR findings in a 32-year-old man with pancreatic VIPoma and liver metastases are described. A 2-cm mass was present in the region of the tail of the pancreas that was best shown on T1-weighted fat-suppressed images as a low-signal intensity mass. Multiple liver metastases were present that showed intense peripheral ring enhancement on immediate post gadolinium spoiled gradient echo images.

Prospective study of provocative angiograms to localize functional islet cell tumors of the pancreas

BACKGROUND

Controversy exists concerning the use of preoperative imaging studies in patients with islet cell tumors. Since 1993 we have evaluated the use of provocative angiography in patients with insulinoma or Zollinger-Ellison syndrome (ZES).

METHODS

Twelve patients with a working diagnosis of insulinoma (n = 4) or ZES (n = 8) were studied. Of the eight patients with ZES, four were known to have multiple endocrine neoplasia type 1. All patients underwent conventional imaging studies followed by provocative angiography. Angiograms were graded based on the ability to detect tumor and regionalize it within the pancreas.

RESULTS

Of the three patients with a working diagnosis of ZES but equivocal results of biochemical studies, none had arteriographic imaging of an islet cell tumor or a positive provocative study result (true negative result). Of the nine patients with documented islet cell tumor, seven (78%) underwent arteriographic imaging of the tumor and eight (89%) had correct regional localization by provocative angiography. Sensitivity and specificity for imaging were 78% and 100%, respectively, and for regional localization 89% and 100%, respectively.

CONCLUSIONS

Provocative angiography is the localization study of choice for both gastrinoma and insulinoma. Having few false-negative results, it can be used to corroborate the diagnosis and, having few false-positive results, it detects tumor and biochemically confirms localization in nearly every patient.

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.

The use of somatostatin receptor scintigraphy in the differential diagnosis of pancreatic duct cancers and islet cell tumors

OBJECTIVE

In the present study, the diagnostic value of somatostatin receptor scintigraphy (SRS) was evaluated in the preoperative workup in patients with pancreatic duct cancers and islet cell tumors, as well as in the follow-up of these patients.

METHODS

Twenty-six patients with suspected primary pancreatic duct cancers and 48 patients with islet cell tumors were studied. The SRS was performed using the radionuclide-labeled somatostatin analogue 111In-octreotide. Another group of 12 patients who were still alive more than 3 years after pancreaticoduodenectomy for pancreatic duct adenocarcinomas also underwent SRS.

RESULTS

In 31 (65%) of 48 patients, the primary pancreatic islet cell tumor as well as its often previously not yet recognized metastases could be visualized. In contrast, none of the 26 pancreatic adenocarcinomas or their metastases could be seen. In 5 of 12 patients who were alive more than 3 years after pancreaticoduodenectomy for pancreatic duct adenocarcinomas, metastatic lesions were visualized at SRS. In retrospect, these patients were not operated on for adenocarcinomas but for "nonfunctioning" islet cell tumors.

CONCLUSIONS

The present study supports the concept that SRS has a place in the preoperative differential diagnosis of islet cell tumors and pancreatic duct cancers as well as in the follow-up, especially in those cases in which no tumor histologic analysis was obtained, or the pathologic examination of the tumor tissue had not included special staining procedures for neuroendocrine characteristics. Our results also indicate that the evaluation of the results of investigations on the role of surgery or radiation therapy and chemotherapy or both in pancreatic duct cancer have to be interpreted with caution, if no histologic analysis and staining for neuroendocrine characteristics was performed.

Operative tumour yield obviates preoperative pancreatic tumour localization in multiple endocrine neoplasia type 1

The efficiency of pancreatic tumour localization was prospectively evaluated in 12 consecutive patients with multiple endocrine neoplasia type 1 (MEN1), who were subjected to extirpation of 56 islet cell neoplasms of 0.2-4 cm in diameter (mean 0.8 cm) during pancreatic resection and enucleation. Computed tomography, angiography of the coeliac trunc and superior mesenteric artery, and percutaneous ultrasound correctly localized 7-12% of the tumours and 21-37% of the 19 lesions measuring at least one centimetre in diameter. Transhepatic portal vein sampling correctly located tumour sites in the proximal or distal portions of the pancreas in four out of six patients, but demonstrated unsatisfactory specificity. Intra-operative ultrasound and bidigital palpation of the pancreas had overall sensitivities of 86 and 45%, respectively, and eight lesions below 0.3 cm in diameter remained undetected with intraoperative ultrasound. It is concluded that diagnosis of endocrine pancreatic neoplasms is biochemical in MEN1 and that broad screening of tumour markers efficiently reveals pancreatic involvement decades before the development of a clinically overt disease. Intra-operative ultrasound is a requisite for pancreatic endocrine surgery in MEN1, and it obviates the need for conventional pancreatic imaging unless a pre-operative search for metastatic disease and anatomical aberrations is considered important.

Management of patients with Zollinger-Ellison syndrome

Zollinger-Ellison syndrome (ZES) is caused by gastrin-secreting tumors called gastrinomas. Patients commonly present with peptic ulcer disease and may have recurrent, multiple, and atypically located ulcers, e.g. in the jejunum. Alternatively, severe diarrhea may be the only presenting symptom. Patients with multiple endocrine neoplasia Type I (MEN-I) and ZES become symptomatic at an earlier age than patients with sporadic ZES. Patients with ZES have elevated fasting serum gastrin concentrations (> 100 pg/ml) and basal gastric acid hypersecretion (> 15 mEq/h). The secretin stimulation test is the best test to distinguish ZES from other conditions resulting in elevated gastrin levels. Gastric acid hypersecretion can be controlled in virtually all patients with H2-receptor antagonists or omeprazole, thus rendering total gastrectomy unnecessary. Computed tomography (CT), magnetic resonance imaging (MRI), radionuclide octreotide scanning, endoscopic ultrasound, and the selective arterial secretin injection test are the recommended imaging studies for localization of gastrinoma; nevertheless, 50% of gastrinomas are not evident on preoperative imaging studies. All patients with sporadic gastrinoma who do not have unresectable metastatic disease should undergo exploratory laparotomy for potential curative resection. With increased awareness of duodenal tumors, gastrinoma can be found in 80-90% of patients. Surgery may be the most effective treatment for metastatic gastrinoma if most or all of the tumor can be resected. The management of patients with MEN-I and ZES remains controversial. Some clinicians advocate an aggressive surgical approach, whereas others have had little success in rendering patients eugastrinemic.