Somatostatin analogue scintigraphy of malignant lymphomas

68Ga-DOTATATE PET/CT Incidentally Detects Relapsed Chronic Lymphocytic Leukemia in Patient With Metastatic Neuroendocrine Tumor

ABSTRACT

A 54-year-old man with metastatic well-differentiated neuroendocrine tumor of the pancreas underwent 68Ga-DOTATATE PET/CT scan to evaluate treatment response. Patient was known for remote history of chronic lymphocytic leukemia (CLL), previously treated. Scan revealed diffusely increased abnormal tracer uptake throughout the marrow of the axial and proximal appendicular skeleton. Bone marrow biopsy revealed relapsed CLL. We present a rare case of relapsed CLL incidentally detected on 68Ga-DOTATATE PET/CT.

Clinicopathologic characteristics and novel biomarkers of aggressive B-cell lymphomas in the nasopharynx

BACKGROUND

The most common nasopharyngeal lymphoma in the United States are B-cell non-Hodgkin lymphomas (B-NHL). Relatively little is known about the clinicopathologic features of these cases. In this study, we characterize a bi-institutional cohort of aggressive B-NHL primary to the nasopharyngeal area. We compare and contrast EBV-positive versus EBV-negative cases and evaluate expression of SSTR2, CD30, and PD-L1, potential markers for targeted therapeutics.

METHODS AND RESULTS

We retrieved 53 cases of aggressive B-NHL from the two institutions. Staining was performed for in situ EBV (EBER), CD30, SSTR2 and PD-L1. The response to initial therapy, disease-free interval, and survival at two- and five-year following initial diagnosis were used as primary clinical outcome. Overall, 13 out of 53 cases (23%) were EBV positive. CD30 expression was more frequent in EBV-positive than in EBV-negative cases (4/6 vs 1/17). Seven of 14 (50%) cases tested demonstrated expression of PD-L1 within tumor cells; the two EBV-positive DLBCL tested showed substantial PD-L1 reactivity. Six of 15 (40%) cases tested were positive for SSTR2. The three EBV-positive patients with available outcome data died within one year of diagnosis; in contrast, the EBV-negative cases showed survival rate of 100% (8/8) and 83% (5/6) at two- and five-year follow-up, respectively.

DISCUSSION

The aggressive B-NHLs of the nasopharynx show differences between EBV-positive versus EBV-negative cases. The association of EBV-positive cases with expression of CD30 and PD-L1 may be particularly informative for targeted therapies. A significant number of cases expresses SSTR2, which could render them susceptible to somatostatin analogue and peptide receptor radionuclide therapies. Finally, our limited case series suggest that EBV negativity may be associated with a better prognosis.

Somatostatin receptor expression in lymphomas: a source of false diagnosis of neuroendocrine tumor at 68Ga-DOTANOC PET/CT imaging

BACKGROUND

⁶⁸Ga-DOTANOC PET/CT is routinely used to image neuroendocrine tumors (NETs). A case of lymphoma initially thought to be NET based on a positive ⁶⁸Ga-DOTANOC PET/CT was recently seen at our institution. This prompted us to determine prospectively somatostatin receptor (SSTR) status in patients with lymphoma by immunohistochemical analysis of SSTR subtypes 2, 3 and 5 (SSTR_2,3,5) and ⁶⁸Ga-DOTANOC PET/CT imaging.

MATERIAL AND METHODS

Twenty-one patients with newly diagnosed lymphoma were referred to ⁶⁸Ga-DOTANOC and FDG PET/CT prior to any treatment. Tracer uptake was evaluated visually by two nuclear medicine specialists. Maximum standardized uptake values (SUVmax) were determined from 14 nodal and two extranodal regions with highest uptake in each patient. Lesions were then graded with Deauville score (1-5) on FDG PET/CT and modified Krenning score (0-4) on ⁶⁸Ga-DOTANOC PET/CT, respectively. SSTR_2,3,5 status was analyzed from routine biopsies of lymphomatous tissue and matched to corresponding PET/CT findings.

RESULTS

About 20/21 patients had FDG-positive lymphoma (Deauville score ≥3). Uptake of ⁶⁸Ga-DOTANOC was regarded as positive if Krenning score was ≥2 and resulted in 13/21 (62%) patients having ⁶⁸Ga-DOTANOC-positive lymphomas. The highest uptake of ⁶⁸Ga-DOTANOC was seen in Hodgkin's lymphoma of nodular sclerosis subtype and in diffuse large B-cell lymphoma (SUVmax median 9.8 and 9.7, respectively). Both cases showed strong SSTR₂ immunopositivity in tumor cells. Some patients had SSTR₂ immunopositivity predominantly in endothelial and dendritic cells and follicular centers of lymph nodes contributing to a positive PET/CT with probably low tumor-specific uptake. SSTR₃ and SSTR₅ were negative in most lymphoma subtypes.

CONCLUSIONS

According to this pilot study, ⁶⁸Ga-DOTANOC PET/CT is positive in some lymphoma subtypes which express SSTRs. These tumors present a potential risk of being misinterpreted as NETs if a representative tumor sample is not available. Lymphomas with high expression of SSTRs may be amenable to treatments targeting these receptors.

Evaluation of a B-cell leukemia-lymphoma 2-specific radiolabeled peptide nucleic acid-peptide conjugate for scintigraphic detection of neoplastic lymphocytes in dogs with B-cell lymphoma

OBJECTIVE

To evaluate use of a radiolabeled peptide nucleic acid-peptide conjugate (RaPP) targeting B-cell leukemia-lymphoma 2 (BCL2) mRNA for scintigraphic detection of neoplastic lymphocytes in dogs with B-cell lymphoma and to assess associations among RaPP uptake, time to tumor progression (TTP), and BCL2 mRNA expression.

ANIMALS

11 dogs with B-cell lymphoma and 1 clinically normal dog.

PROCEDURES

Scintigraphic images were acquired 1 hour after IV injection of the RaPP. Regions of interest (ROIs) were drawn around lymph nodes, liver, and spleen; ROI intensity (relative to that of an equally sized region of muscle in the same image) was measured. Each ROI was also subjectively categorized as positive or negative for increased RaPP uptake. Expression of BCL2 mRNA was determined via quantitative reverse transcriptase PCR assay of a lymph node sample from dogs with lymphoma. Associations among imaging results, TTP, and BCL2 mRNA expression were evaluated.

RESULTS

Increased RaPP uptake was detected in affected tissues of dogs with lymphoma. Dogs with superficial cervical lymph node ROIs categorized as negative (n = 8) for increased RaPP uptake had a significantly longer TTP than did dogs for which this ROI was considered positive (2). Measured intensity of mandibular and superficial cervical lymph node ROIs was negatively associated with TTP. Associations among BCL2 mRNA and ROI intensity or TTP were not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased RaPP uptake at mandibular or superficial cervical lymph node ROIs may be a negative prognostic indicator in dogs with lymphoma. A larger investigation is needed to determine clinical value of the RaPP for disease detection and prognostication.

Future clinical prospects in somatostatin/cortistatin/somatostatin receptor field

Somatostatin receptors (sst), somatostatin (SS) and cortistatin (CST) are widely expressed in the various systems in the human and rodent organisms and are "responsible" for maintaining homeostasis, which is essential for survival. Because of their broad expression pattern sst, SS and CST interactions may play regulatory roles in both physiology and pathophysiology in mammalian organisms. SS analogue treatment strategies as well as the use of SS analogues for diagnostic purposes have been established in diseases of different origins. This review focuses on the currently determined role for SS analogues in today's clinical practice and the potential clinical prospects for SS, CST and sst interactions in the future, with a focus on neuroendocrine and non-neuroendocrine tumours and immune-mediated diseases. Moreover, the role of new SS analogues and new insights in sst physiology will be discussed.

The role of cortistatin in the human immune system

Cortistatin (CST) is a recently described neuropeptide that shares high homology with somatostatin (somatotropin release-inhibiting factor, SRIF) and binds with high affinity to all somatostatin (sst) receptor subtypes. CST is currently known to have a widespread distribution in many human organs including the immune system. The activities specific to CST may be partially attributable to its binding to the growth hormone secretagogue (GHS)-receptor (GHS-R) and the orphan G-protein-coupled receptor MrgX2. Human immune cells produce CST, whereas macrophage lineage and activated endothelium express sst2, and human lymphocytes express sst3. The human thymus expresses sst1, 2, 3, MrgX2 and almost all immune cells express GHS-R. Moreover, at this very moment promising research with CST in experimental animal models is being performed. On the basis of these promising results, studies aiming to further evaluate the possibilities of CST as a therapeutic agent in human immune-mediated inflammatory diseases are warranted.

Initial Staging of Lymphoma With Octreotide and Other Receptor Imaging Agents

Somatostatin receptor scintigraphy is useful in diagnosing tumors with increased expression of somatostatin receptors. The correct use of this technique reveals the localization of neuroendocrine primary tumors and unknown metastases in approximately 90% of patients. However, somatostatin receptor scintigraphy also can image many other human tumors expressing somatostatin receptors, including malignant lymphomas and thymomas. The sensitivity of somatostatin receptor scintigraphy to image somatostatin receptor-positive tumors is very high, but due to the variable expression of specific receptor subtypes, the specificity can be relatively low. This drawback is crucial in evaluating lymphoproliferative diseases, or, in general, when immune cells are involved. The sensitivity of somatostatin receptor scintigraphy for Hodgkin's lymphoma is 95%-100%, whereas for non-Hodgkin's lymphoma it is around 80%. It has been shown that the uptake of [(111)In-DTPA(0)]octreotide in lymphomas is lower compared to the uptake in neuroendocrine tumors. This is mainly attributed to the low number of receptors on immune cells compared to neuroendocrine cells; however, ligand-induced internalization and differential receptor regulation may also participate in determining this phenomenon. Therefore, caution should be taken when interpreting data from some studies. Several new ligands are currently under study to improve these limits and the expression of other neuropeptide receptors is being investigated to provide a molecular basis for in vivo multireceptor targeting of tumors. With the use of currently available somatostatin analogs, somatostatin receptor scintigraphy does not seem to have a significant impact in patients with lymphomas for diagnostic purposes. There are a few exceptions, however. Among these, the staging and restaging of extragastric lymphoma MALT-type may present some advantages. Conversely, somatostatin receptor scintigraphy in the imaging of thymic malignancies could enhance both our diagnostic and therapeutic capabilities. Somatostatin receptor scintigraphy is diagnostically relevant in differentiating malignant from benign lesions, especially in those patients with associated paraneoplastic syndromes, and is the main criterion to select patients suitable for therapy with somatostatin analogs. Recent findings emerging from in vitro studies on somatostatin receptor physiology in immune cells will certainly reopen and expand the potential applications of somatostatin analogs for in vivo diagnostic and therapeutic options.

Growth inhibition of experimental non-Hodgkin's lymphomas with the targeted cytotoxic somatostatin analogue AN-238

The cytotoxic analogue of somatostatin, AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201), a superactive derivative of doxorubicin (DOX), linked to somatostatin analogue carrier RC-121 binds with high affinity to receptors for somatostatin and can be targeted to tumors that express these receptors. Because somatostatin receptors are found in a high percentage of human non-Hodgkin's lymphomas (NHLs), we evaluated the antitumor effect of AN-238 in 2 human NHL cell lines in vivo. Nude mice bearing xenografts of RL and HT human NHL were treated with AN-238 or its components at equimolar doses, and antitumor effects were determined. Expression of mRNA for somatostatin receptor subtypes was measured by RT-PCR, and the presence of somatostatin receptors was determined by radioligand binding. Toxicity was evaluated by following white blood cell count (WBC) and body weight. AN-238 significantly (p < 0.05) inhibited growth of RL and HT xenografts and prolonged the tumor doubling time. Cytotoxic radical AN-201, the unconjugated mixture of somatostatin analogue RC-121 and AN-201 or RC-121 alone had no significant effects. Blockade of somatostatin receptors by excess RC-121 abolished the effect of AN-238, demonstrating targeting. Expression of somatostatin receptors was not changed after repeated treatment with AN-238. AN-201, but not AN-238, significantly lowered the WBC and caused a greater decrease in body weight than AN-238. Our findings demonstrate that targeted chemotherapy with AN-238 can strongly inhibit the growth of NHL cells, which express somatostatin receptors. AN-238 could be considered for the treatment for patients with NHL.

Receptor Imaging in Oncology by Means of Nuclear Medicine: Current Status

To date, our understanding of the role of receptors and their cognate ligands in cancer is being successfully translated into the design and development of an arsenal of new, less toxic, and more specific anticancer drugs. Because most of these novel drugs are cytostatic, objective response as measured by morphologic imaging modalities (eg, computed tomography or magnetic resonance imaging) cannot be used as a surrogate marker for drug development or for clinical decision making. Positron emission tomography (PET) can be used to image and quantify the in vivo distribution of positron-emitting radioisotopes such as oxygen-15, carbon-11, and fluorine-18 that can be substituted or added into biologically relevant and specific receptor radioligands. Similarly, single-photon emission computed tomography (SPECT) can be used to image and quantify the in vivo distribution of receptor targeting compounds labeled with indium-111, technetium-99m, and iodine-123. By virtue of their whole-body imaging capacity and the absence of errors of sampling and tissue manipulation as well as preparation, both techniques have the potential to address locoregional receptor status noninvasively and repetitively. This article reviews available data on the in vivo evaluation of receptor systems by means of PET or SPECT for identifying and monitoring patients with sufficient receptor overexpression for tailored therapeutic interventions, and also for depicting tumor tissue and determining the currently largely unknown heterogeneity in receptor expression among different tumor lesions within and between patients.

Somatostatin receptor distribution and function in immune system

Somatostatin and cortistatin, a recently discovered endogenous neuropeptide relative of somatostatin, have multiple modulatory effects on the immune system. The specific somatostatin receptor distribution might in part explain the heterogeneity of effects of somatostatin or its analogs on immunocytes. In fact, somatostatin receptor subtypes are differentially expressed on specific cell subsets within the organs of the immune system and the expression is dynamically regulated and seems to depend on the traffic of these cells through and within lymphoid structure and homing in tissues. Somatostatin effects on immune cells are mainly based on autocrine and paracrine modes of action. In fact, activated cells producing somatostatin (or cortistatin) may interact with other cells expressing the receptors. Here, we review the postulated modes of action of somatostatin and somatostatin-like peptides, including the currently available synthetic somatostatin analogs, in cells of the immune system. We also discuss the wide distribution of somatostatin and its specific five receptor subtypes in immune cell lines, as well as throughout animal and human lymphoid organs, in both normal and pathological conditions.

Peptide Targeted Imaging of Cancer

After the discovery of several specific peptide receptors in a variety of cancer types more than 10 years ago, radiolabeled peptide analogs with adequate stability, receptor binding properties, and biokinetic behavior were introduced for imaging of neuroendocrine tumors, several adenocarcinomas, lymphoma, and melanoma. Although initially 123I or 111In were used for labeling, recent efforts have also concentrated on 99mTc or PET-radionuclides (18F,68Ga), as they result in better image resolution with lower radiation dose to patients. Scintigraphy with labeled somatostatin analogs (99mTc, 111In,18F,68Ga), with 123I-labeled vasoactive intestinal peptide, and recently 99mTc-bombesin/GRP-or-111In gastrin analogs, have shown a mean sensitivity of greater than 85% to localize deposits of tumors, with appropriate receptor expression frequently scarcely visible with other imaging procedures. Moreover, these observations introduced peptide-targeted metabolic radiotherapy for metastatic cancers. This development has produced a considerable amount of preclinical studies to broaden the impact of labeled peptide ligands on the management of cancer.

Gallium-67 scintigraphy: a cornerstone in functional imaging of lymphoma

Until recently, gallium-67 scintigraphy (GS) has been the best available functional imaging modality for evaluating patients with non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD). The diagnostic accuracy of GS in detecting lymphoma is based on optimisation of the imaging protocol, knowledge of potential physiological and benign sites of (67)Ga uptake, and the Ga avidity characteristics of the individual lymphoma. As (67)Ga is a tumour viability agent, the role of GS is primarily at follow-up. A residual mass persisting on CT after treatment poses a common clinical dilemma: it may indicate the presence of viable lymphoma, which requires further treatment, or it can be benign, consisting of only fibrotic and necrotic tissues. GS can successfully differentiate between these conditions. Routine follow-up with GS may allow early diagnosis of recurrence and early institution of treatment. Reversion of a positive GS to a negative test, and the rapidity with which this occurs has a high predictive value for the outcome of the individual patient. Lymphoma showing a normal GS early during treatment has a better prognosis than lymphoma with persistence of pathological findings. Other tumour-seeking single-photon emitting agents, such as thallium-201, technetium-99m methoxyisobutylisonitrile and indium-111 octreotide, have been investigated in lymphoma, primarily as an alternative to GS in specific clinical settings, but are of limited value. The role of radioimmunoscintigraphy is gaining importance in conjunction with radioimmunotherapy. Fluorine-18 fluorodeoxyglucose (FDG) imaging of lymphoma using either dedicated or camera-based PET systems is gradually replacing GS for assessment of lymphoma. FDG overcomes some of the limitations of GS while sharing its tumour viability characteristics. The extensive clinical knowledge and experience accumulated over three decades with GS in lymphoma provides a solid background as well as a model for the assessment of new functional imaging techniques.

Somatostatin receptor imaging

[(111)In-DTPA(0)]octreotide is a radiopharmaceutical with a great potential for the visualization of somatostatin receptor-positive tumors. The overall sensitivity of Somatostatin Receptor Imaging (SRI) to localize neuroendocrine tumors is high. In a number of neuroendocrine tumor types, as well as in Hodgkin's disease, inclusion of SRI in the localization or staging procedure may be very rewarding, either in terms of cost-effectiveness, patient management, or quality of life. The value of SRI in patients with other tumors, like breast cancer, or in patients with granulomatous diseases, has to be established. The development of Peptide Receptor Radionuclide Therapy (PRRT) is expected to stimulate peptide receptor imaging.

Neuroendocrine aspects of immunolymphoproliferative diseases

Exchange of information occurs between cells of neuroendocrine and immune systems. Neuroendocrine hormones may modulate lymphoid cell activities, including proliferation and mitogenesis, and immune cells may produce neuropeptides as well. Neuropetide Y is synthesized in B-cell leukaemia lymphoblasts, while substance P immunoreactivity has been detected in neoplastic haematological samples of different types of leukaemias. The presence of receptors for neuropeptides on different animal and human lymphoid cell lines, as well as in several types of animal and human lymphoproliferative diseases has been demonstrated. Species variability in receptor distribution has been shown as well. Receptor expression in immune cells may be regulated by changes in microenvironmental conditions, it may also be related to the activation and/ or proliferation state of cells. Vasoactive intestinal peptides receptors have been detected in myeloma cells, while somatostatin receptors have been first detected in vitro on resting lymphocytes and cells of the monocyte/macrophage lineage, and later on human activated lymphocytes and on lymphoblastic leukaemia cells. Somatostatin receptors have been found in biopsies from patients with malignant lymphomas. Tumor localization in non-Hodgkin lymphomas and Hodgkin's disease can be visualized by in vivo somatostatin receptor scintigraphy, contributing to establish the diagnosis and the stage of the disease. Recently. somatostatin receptors have been in vivo and in vitro detected in human thymic tumors. Although treatment of lymphoproliferative diseases with somatostatin analogs is a little explored field, partial remission was found in patients with low-grade non-Hodgkin lymphoma and cutaneous T-cell lymphoma, and a successful treatment with octreotide has been reported in patients with thymoma. Specific somatostatin receptors present in progenitors of immune cells are not expressed in the mature phenotype, while they can be detected in transformed cell lines. The possibility that this phenomenon is caused by oncogene expression cannot be ruled out. Moreover, preliminary data showed a developmental expression of somatostatin receptors in lymphoid cells, suggesting a potential role for neuropeptide receptors as differentiation markers. Although controlled studies are warranted to investigate the efficacy of the currently available analogs, somatostatinergic compounds may be of interest in the treatment of lymphoproliferative malignancies. A promising approach in refractory patients with somatostatin receptor positive malignant lymphomas may be radionuclide-targeted and cytotoxic analog therapy. These concepts increase the possibility of a wider antitumor treatment with ligands for neuroepeptide receptors than in established 'classic' neuroendocrine tumors.

Functional imaging of Langerhans cell histiocytosis by (111)In-DTPA-D-Phe(1)-octreotide scintigraphy

BACKGROUND

Langerhans cell histiocytosis is a rare group of diseases of unknown pathogenesis, variable clinical presentation, and behavior. It encompasses highly aggressive, often fatal, and indolent diseases, with a variety of intermediate forms between the two extremes. Localization and monitoring of Langerhans cell histiocytosis deposits are based on the combined use of different imaging modalities, which include magnetic resonance, computed tomography, and nuclear medicine procedures. Somatostatin receptor scintigraphy recently has been used to image immune-mediated diseases with excellent results.

METHODS

In this study, the authors have evaluated the potential role of somatostatin receptor scintigraphy by using (111)In-DTPA-D-Phe(1)-octreotide in a series of patients with Langerhans cell histiocytosis. Eight consecutive patients (2 males, 6 females; mean age, 43 years; age range, 29-60 years) with histologically proven Langerhans cell histiocytosis, in various phases of their disease, were imaged 24 hours after intravenous injection of 111-222 MBq of (111)In-DTPA-D-Phe(1)-octreotide, by using total body and spot view images. The objective of the study was to preliminarily evaluate this technique in the evaluation of Langerhans cell histiocytosis.

RESULTS

Most Langerhans cell histiocytosis deposits were clearly documented by somatostatin receptor scintigraphy, independently from the anatomic location (i.e., skeleton, mucosae, soft tissue, etc.). The correlation between conventional imaging modalities and somatostatin receptor scintigraphy results was fairly good, though this was not considered a primary objective of the study.

CONCLUSIONS

Among the various imaging modalities for Langerhans cell histiocytosis, somatostatin receptor scintigraphy is unique, because it accurately depicts the active sites of disease and thus can help in monitoring the response to treatment, together with conventional imaging modalities. Further studies are necessary to confirm the diagnostic value of this technique and clarify the biologic significance of the expression of somatostatin receptors in Langerhans cell histiocytosis.

Somatostatin is a selective chemoattractant for primitive (CD34(+)) hematopoietic progenitor cells

OBJECTIVE

Somatostatin (SST) is a regulatory peptide with a wide variety of activities in different tissues. SST activates G(alpha i)-protein-coupled receptors of a family comprising five members (SSTR1-5). Despite the broad use of SST and its analogs in clinical practice, the spectrum of activities of SST is incompletely defined. Here, we examined the role of SST and its receptors in hematopoiesis.

MATERIALS AND METHODS

SSTR expression on human and mouse hematopoietic cells was analyzed by flow cytometry and reverse transcriptase polymerase chain reaction. The effects of SST on cell migration were measured in transwell assays. Using selective inhibitors, signaling mechanisms involved in SSTR2-mediated migration were studied in 32D cell transfectants expressing SSTR2.

RESULTS

Human hematopoietic cells exclusively expressed SSTR2, whereas mouse bone marrow cells expressed SSTR2 and SSTR4. SSTR levels were high on primitive (CD34(+), Lin(-)) but low or absent on more mature (CD34(-), Lin(+)) cell types. Both SST and its analog octreotide acted as chemoattractants for primitive hematopoietic cells. Despite the presence of SSTR4, bone marrow cells from SSTR2-deficient mice failed to migrate toward SST gradients, suggesting that SSTR2 and SSTR4 are functionally different in this respect. SST activated phosphatidylinositol 3-kinase and the MAP kinases Erk1/2 and p38 in 32D[SSTR2] cells. While chemical inhibitors of these kinases had some effect, SST-induced migration was most strongly affected by blocking G(alpha i) activity or by elevating intracellular cAMP levels.

CONCLUSIONS

Somatostatin acts as a selective chemoattractant for immature hematopoietic cells via activation of multiple intracellular pathways.

Internalization-defective mutants of somatostatin receptor subtype 2 exert normal signaling functions in hematopoietic cells

The regulatory peptide somatostatin (SST) acts via a family of G-protein-coupled receptors comprising five subtypes (SSTR1-5). G-protein-coupled receptors activate multiple signaling mechanisms, which variably depend on internalization and intracellular routing of activated receptors. We have recently demonstrated that hematopoietic precursors express SSTR2 and that SST is a chemoattractant for these cells. Herein, we characterize critical regions in SSTR2 involved in endocytosis and describe how ligand-induced internalization impacts on two major signaling functions of SSTR2 in hematopoietic cells, the activation of the Erk pathway and the induction of promigratory responses.

Somatostatin induces migration of acute myeloid leukemia cells via activation of somatostatin receptor subtype 2

Somatostatin, a neuropeptide with multiple activities, exerts its function via G-coupled membrane receptors. Five somatostatin receptor subtypes, sst1-5, have been identified. We have recently established that somatostatin acts as a chemoattractant on normal hematopoietic progenitor cells. Here, we studied the expression of somatostatin receptors (sst) on leukemic cells from 16 AML patients. Using fluorescent somatostatin (Fluo-SS) in flow cytometry, we found that sst are expressed in variable amounts on primary AML cells. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis and immunochemistry revealed that only sst subtype 2 is expressed by AML cells. Using a two-chamber in vitro migration assay, we show that AML cells migrated towards a gradient of octreotide, a stable synthetic analogue of somatostatin. The degree of migration correlated with the cell surface density of sst2 as measured by Fluo-SS binding. These findings indicate that somatostatin influences trafficking of AML cells, which may have implications for the distribution of AML cells in the body and for clinical applications of somatostatin and analogues thereof in the context of AML.

Somatostatin receptor scintigraphy useful in stage I-II Hodgkin's disease: more extended disease identified

Somatostatin receptor (SS-R) scintigraphy successfully shows primary cancers and metastases in patients with a variety of SS-R-positive tumours. In vitro studies have shown that SS-Rs are present in lymph nodes from patients with Hodgkin's disease (HD). We performed a prospective study in 126 newly diagnosed patients with HD and compared the results of SS-R scintigraphy with conventional staging procedures, i.e. physical examination, computerized tomography (CT) scanning and other imaging techniques. We report positive scintigraphy in all patients. The lesion-related sensitivity was 94% and varied from 98% for supradiaphragmatic lesions to 67% for infradiaphragmatic lesions. In comparison with CT scanning and ultrasonography, SS-R scintigraphy provided superior results for the detection of Hodgkin's localizations above the diaphragm. In the intra-abdominal region, the CT scan was more sensitive than the SS-R scan. A false-positive scan was rarely seen. In stages I and II supradiaphragmatic HD patients, SS-R scintigraphy detected more advanced disease in 18% (15 out of 83) of patients, resulting in an upstaging to stage III or IV, thus directly influencing patient management. Our data would support the validity of SS-R scanning as a powerful imaging technique for the staging of patients with HD.

The use of nuclear medicine in infections

The spectrum of infectious diseases has changed over the last few years, hence the requirements for radionuclide imaging for the detection of infection are becoming more demanding so that, although gallium-67 and labelled leucocytes remain useful agents, there is currently great interest in the development of new agents especially able to target chronic, non-pyogenic inflammation. Agents can be classified according to the site at which the radiolabel is targeted: pre-endothelial (for example, labelled leucocytes), endothelial (for example, labelled anti-endothelial monoclonal antibodies) or post-endothelial (for example, fluorine-18-fluorodeoxyglucose (FDG)). 67Ga and labelled polyclonal human immunoglobulin (HIG) localize at inflammation initially as a result of increased endothelial permeability, followed by retention of the label through binding to local extravascular receptors. Labelled leucocytes are avidly taken up by acute pyogenic inflammatory foci but perform less well in chronic inflammation. Other indications for labelled leucocytes include bone infection and undiagnosed fever. Nevertheless, since many causes of the latter do not stimulate a neutrophilic infiltrate, a non-specific agent, such as 67Ga, FDG or HIG, may be preferable, especially in patients with no immediate significant medical history. Since endothelial E-selectin expression is closely correlated to lymphocyte migration, labelled anti-E-selectin monoclonal antibody may also have a potential role for imaging chronic inflammation.

Expression of somatostatin receptor subtype 2 mRNA in human lymphoid cells

We analyzed the mRNA expression of somatostatin receptor subtypes 1 to 5 (SSTR1-5) in human lymphoid cell lines, human peripheral blood lymphocytes (PBL), and human lymphatic leukemia cells, using the reverse transcription-polymerase chain reaction method. In human lymphoid cell lines, SSTR2 mRNA expression was clearly detectable, and there was no evidence of SSTR1 mRNA expression. SSTR2 mRNA was barely detectable in PBL from healthy individuals but was clearly detectable in EB virus-transformed lymphocytes. Lymphocytes from some of the leukemic patients showed elevated SSTR2 mRNA expression. SSTR2 mRNA expression in PBL was upregulated upon stimulation by PHA. SSTR3 mRNA was also observed in all the cell lines examined, although in one cell line, the expression was weak. Some cell lines showed little or no SSTR4 or 5 mRNA expression. The expression pattern of SSTR2 mRNA suggests that this receptor may have some important roles in lymphocyte activation, development, and/or tumorgenesis.

Somatostatin receptor scintigraphy in the staging of lymphomas

In this prospective study we evaluated the somatostatin receptor scintigraphy in the initial staging of 19 patients suffering from Hodgkin's (HD) and non-Hodgkin's lymphomas (NHL) and in the restaging of 16 patients. Scintigraphy was compared to the results of the methods applied for adequate staging of lymphoma patients in the large multicentre trials. Planar imaging and SPECT was performed after intravenous injection of 110 or 220 MBq of 111In-pentetreotide. The patient-based analysis yielded an overall sensitivity of 88%, contrasting lesion-based sensitivities of 57%, 35%, and 43% in HD, low-grade NHL and high-grade NHL, respectively. The best results were obtained in the head-and-neck region and the worst in the abdomen (sensitivities of 61% and 24%, respectively). Bone marrow infiltration was visible in 1/12 cases only. There was no significant difference between the outcomes of patients in the initial staging and restaging and no influence of the amount of injected radiopharmaceutical on the results. In terms of the Ann-Arbor classification, 10/35 patients were concordant whereas 22 were understaged and 3 overstaged scintigraphically. In conclusion, somatostatin receptor scintigraphy is not useful in the initial staging or restaging of malignant lymphomas, especially NHL, due to low lesion detection rates most probably because of low receptor densities. In addition, intraindividual heterogeneity of somatostatin receptor expression has to be considered.

Receptor scintigraphy of non-neuroendocrine cancers with In-111 pentetreotide

Somatostatin receptors (SR) are surface markers characterizing not only APUDomas associated with neuroendocrine identities but also malignancies without neuroendocrine expression. Recently, the somatostatin analog pentetreotide was labeled with In-111 (OctreoScan 111, Mallinckrodt Medical BV, Petten, Holland) and introduced for the in vivo visualization in man of SR-positive tissues. In the present report, SR-specific scintigraphy is evaluated as a clinical tool for tissue characterization in correlation with histological and radiological examinations. Scintigraphy was focused and performed in cancer types without neuroendocrine tissue expression such as brain (n = 6) and breast tumors (n = 9) and lymphomas (n = 5). Scintigraphy was performed for comparison at 6 and 22 h after i.v. application of 111 MBq (3 mCi) of In-111-Pentetreotide. In the breast cancer group, the primary tumor was visualized in all 9 women as well as in all 4 cases with palpable axillary lymph nodes. Three women with a negative axillary node scan and impalpable nodes had positive biopsy. In two cases, mediastinal lymph node involvement was observed. So far the role of SR-positive breast cancer (BC) scans remains unknown. It is tempting to speculate that in resected women who are histologically and scintigraphically SR positive, it might be of value in the early detection of symptom-free recurrences. High densities of SR were present within both meningiomas, the high-grade astrocytoma and the craniopharyngioma. Differentiation of low- and high-grade astrocytomas could not be successfully achieved because both grades showed intense radioactivity uptake, even though high-grade tumors lack SR. The latter might be due to the damaged blood-brain barrier and the poor radioactivity washout observed in high-grade astrocytomas. All five lymphomas could be detected due to the presence of activated lymphocytes and macrophages that express SR at a sufficient density. In conclusion, SR scintigraphy in non-neuroendocrine malignancies does not seem to be reliable for an initial tumor staging but rather more suitable for a tissue characterization and extremely useful for monitoring changes of SR expression after treatment.

Noninvasive differentiation of meningiomas from other brain tumours using combined 111Indium-octreotide/99mtechnetium-DTPA brain scintigraphy

We have studied prospectively 47 patients with CNS tumours including 16 meningiomas and 33 other tumours using combined 111In-octreotide and 99mTc-DTPA brain scintigraphy. 111In-octreotide scintigraphy was used to image somatostatin receptors (SSR) and 99mTc-DTPA scintigraphy was used to assess the integrity of the blood-brain barrier (BBB). A total of 32 tumours (65%) were detected. All SSR positive tumours also had positive 99mTc-DTPA scans and all SSR negative tumours were negative on 99mTc-DTPA scans. Among the tumours located outside the BBB, all meningiomas and two out of six schwannomas were positive on combined SSR/99mTc-DTPA scintigraphy. Among the tumours located inside the BBB, seven out of nine gliomas grade I-III were negative, whereas all glioblastomas were positive. Other positive tumours included one malignant non-Hodgkin lymphoma and two cerebral metastases. SSR scintigraphy alone was non-specific in the diagnosis of meningiomas, as 16 non-meningiomatous tumours also had positive SSR scans probably due to a breakdown of the BBB (excluding the malignant lymphoma). Measuring the tumour-to-background ratio on SSR scans improved specificity, but sensitivity was decreased below 70% because some meningiomas were only slightly positive. Only the ratio of SSR scintigraphy to conventional 99mTc-DTPA brain scintigraphy (SSR-to-BS index) allowed a reliable differentiation of meningiomas from other CNS tumours, most notable from schwannomas (sensitivity: 94%; specificity: 100%). Our results support the usefulness of combined SSR and conventional brain scintigraphy in the noninvasive pre-operative diagnosis of meningiomas.

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 relevance of somatostatin receptor expression in malignant lymphomas

Somatostatin (SRIF) receptor (sst) expression on lymphoid cells may be related to activation or proliferation of these cells. We investigated the effectiveness of sst scintigraphy in the staging of malignant lymphomas compared with conventional methods. One hundred twenty-six patients with newly diagnosed, histologically proven malignant lymphoma (54 with Hodgkin's disease [HD] and 72 with non-Hodgkin's lymphoma [NHL]) received 111In-labeled DTPA-octreotide (> 200 MBq 111In) and were assessed by planar total-body scintigraphy and single-photon emission computed tomography (SPECT) images of the upper abdomen. The sst scintigraphy was positive in 98% of HD patients. Compared with conventional methods, additional lymphomas were detected in 37%, while lesions escaped detection in 7% (all located in the abdomen); 10 HD patients were downgraded and one was upgraded. The sst scintigraphy was positive in 85% of NHL patients, but positivity did not correlate with the degree of malignancy. Additional lesions were detected in 21% of NHL patients, with false-negatives in 7% and upgrading in 13 NHL patients. The results indicate that sst scintigraphy is sensitive in patients with HD and NHL and may reveal sites of active disease undetected by conventional methods, making it a useful diagnostic tool for malignant lymphomas. Further studies should define its value in clinical management.

Somatostatin receptor scintigraphy in cutaneous malignant lymphomas

BACKGROUND

Lymphoid cells may express somatostatin receptors (SS-Rs) on their cell surface. Therefore radiolabeled somatostatin analogues may be used to visualize SS-R-positive lymphoid neoplasms in vivo. Exact staging is the basis for treatment decisions in cutaneous malignant lymphoma. We considered the possibility that SS-R scintigraphy might offer a clinically useful method of diagnostic imaging in patients with cutaneous malignant lymphoma.

OBJECTIVE

We evaluated SS-R scintigraphy in comparison with conventional staging methods in the staging of cutaneous malignant lymphoma.

METHODS

We conducted a prospective study in 14 consecutive patients with histologically proven cutaneous malignant lymphoma. SS-R scintigraphy was compared with physical, radiologic, and bone marrow examinations. Lymph node excisions were performed in patients with palpable lymph nodes.

RESULTS

SS-R scintigraphy was positive in the lymph nodes in all four patients with malignant lymph node infiltration and negative in the three patients with dermatopathic lymphadenopathy. In two patients, previously unsuspected lymphoma localizations were visualized by SS-R scintigraphy. In only three patients all skin lesions were visualized by SS-R scintigraphy; these three patients had not been treated with topical corticosteroids. SS-R scintigraphy failed to detect an adrenal mass in one patient and bone marrow infiltration in two patients.

CONCLUSION

SS-R scintigraphy may help distinguish dermatopathic lymphadenopathy from malignant lymph node infiltration in patients with cutaneous malignant lymphoma.

New diagnostic imaging procedures in Hodgkin's disease

A variety of new diagnostic imaging methods have been developed in recent years for patients with Hodgkin's disease in an attempt to improve the detection of spleen and bone marrow involvement within the scope of staging and to discriminate between fibrosis and vital lymphoma after treatment. Somatostatin receptor scintigraphy has been performed only in a small number of patients to date and further studies must be conducted. Magnetic resonance imaging (MRI), as the established method, has shown its potential in several studies in detecting both spleen and bone marrow involvement; MRI investigations, however, only visualize a limited portion of the body and therefore must be performed in areas of clinically suspected disease. Immunoscintigraphy with radiolabeled antibodies is still in a preclinical or at most early clinical stage of evaluation and first results have to be confirmed in a controlled trial. Positron emission tomography (PET) with [18F]fluorodeoxy-glucose (FDG) is a technique which is still not a routine clinical procedure. However, whole-body FDG-PET seems to be a promising method in staging and follow-up of lymphoma, because it offers the unique capability of visualising metabolic activity throughout the entire body. Long-term multicenter studies are necessary to confirm these promising initial data. In the future, wholebody FDG-PET will probably be the technique of choice for immunoscintigraphic studies with radiolabeled monoclonal antibodies and studies on the pharmacokinetics of cytostatic compounds.

Indium-111 pentetreotide scintigraphy in malignant lymphomas

Somatostatin receptor imaging (SRI) was carried out as part of the initial staging of 26 patients with histologically proven Hodgkin's (3) and non-Hodgkin's (23) lymphoma, and in the assessment of the first treatment's efficacy in seven of these patients. Static acquisitions over the whole body were performed 4 and 24 h after intravenous administration of 150 MBq of indium-111 pentetreotide. SRI data were compared with the results of conventional methods (clinical data, abdominal and thoracic computed tomography, bone marrow biopsy). Only 50 of the 86 (58%) confirmed extra-medullary tumour sites were detected by SRI. Twelve previously unknown localizations were visualized in seven patients. The Ann Arbor clinical stage was modified in only one of them. When tumoral tracer uptake was present, a tumour uptake index (TUI) was calculated using two regions of interest (one over the tumoral hot spot and one over the shoulder) on 24-h planar images. The patients were classified into three groups: high tumour uptake (TUI > 2.5 in all tumour sites, group A, six patients), low tumour uptake (1.5 < TUI < 2.5 in all tumour sites, group B, 18 patients), and no tumour uptake (group C, two patients). The sensitivity of SRI detection was higher in group A (90%) than in group B (52%) (P < 0.001). Six weeks after the fourth chemotherapy cycle, conventional methods and SRI were concordant in five of seven investigated cases (four complete remissions and one residual active thoracic mass showing tracer uptake), and discordant in two. SRI demonstrated residual tumoral tracer uptake in these two patients, who had previously been considered to be in complete remission. In conclusion, SRI does not seem to be reliable for the initial staging of lymphomas because of the highly variable and usually low tumoral tracer uptake. It may be more useful in the diagnosis of residual masses after treatment. However, further studies are needed to assess its specificity.

Somatostatin and its cyclic octapeptide analog SMS 201-995 as inhibitors of proliferation of human acute lymphoblastic and acute myeloid leukemia

Somatostatin (SS) is a 14 amino acid peptide which is secreted by the hypothalamus and the pancreatic islets. It expresses antiproliferative activity in various organ systems, experiments have suggested effects of SS on hematopoietic cells. Here we present investigations regarding the effect of SS and its analog SMS 201-995 (SMS) on the in vitro proliferation of acute lymphoblastic leukemia (ALL; n = 7 cases), acute myeloid leukemia (AML; n = 21 cases) and chronic lymphocytic leukemia (CLL; n = 2 cases). Both SS and SMS inhibited spontaneous leukemic cell growth in approximately 1/3 of cases (i.e. 7/19). G-CSF stimulated AML cells were inhibited by SMS in 11/21 cases. AML cell proliferation induced by IL-3 or GM-CSF was suppressed in only 3/21 and 6/21 cases, respectively. In ALL cells, IL-7-induced proliferation was suppressed by SMS in 3/7 cases. The effect of SMS seemed to depend on the type of the hematopoietic growth factor, and on their concentrations. In fact, high concentrations of G-CSF could override SMS blocking completely. Colony formation by normal marrow progenitors and DNA synthesis by HL-60 and T11/65 leukemic cell lines were not affected by SMS. In conclusion, somatostatin may act as a negative regulator of the proliferative activity of human leukemia.

Somatostatin-receptor imaging in lymphoma

Patients with Hodgkin's or non-Hodgkin's lymphoma are staged for treatment based on the extent of known disease involvement and the histopathologic grading of the disease. Radiological techniques, including computed tomography, usually depend on estimates of lymph node enlargement and mass effects as the criterion for disease involvement. Lymphomatous tissue obtained at surgery has shown high-density somatostatin receptors. Several groups have evaluated the utility of 111In-DTPA-pentetreotide (Octreoscan, Mallinckrodt, St. Louis, MO) to detect lymphomatous tissue for more accurate staging of patients with lymphoma. The procedure is safe; both Hodgkin's and non-Hodgkins disease involvement is identified. The results, however, have not been uniformly predictive of disease involvement. Consequently, the routine use of this technique in place of currently used anatomic imaging methods is not recommended at this time. The significance of detecting somatostatin receptors in vivo in patients with malignant lymphoma requires further study.

A rare case of primary skeletal muscle lymphoma: the value of octreotide scintigraphy

We report a case of non-Hodgkin lymphoma presenting as a painless mass of the quadriceps femoris muscle that was detected by a somatostatin analogue (octreotide) scintigraphy. We review the few reported cases of primary muscular lymphoma and discuss the potential value of octreotide imaging as a new diagnostic tool.

Comparison of technetium-99m methoxyisobutylisonitrile and gallium-67 citrate scanning in the assessment of lymphomas

The aim of this study was to compare the value of scintigraphy using technetium-99m methoxyisobutylisonitrile (MIBI) with that of scintigraphy using gallium-67 citrate in the assessment of Hodgkin's disease and non-Hodgkin's lymphoma and to relate these results with those of CT scan and MRI. Fifty-eight patients were included either for a follow-up examination or for monitoring of their treatment. Twenty-three residual masses were studied. A whole-body scan was performed, followed by single-photon emission computed tomography (SPET) 20 min after injection of 740 MBq of 99mTc-MIBI and 72 h after injection of 185 MBq of 67Ga citrate. The overall sensitivity of 99mTc-MIBI and 67Ga citrate was 71% and 68%, respectively, and the overall specificity was 76% and 44%, respectively. For residual masses, the sensitivity was 44% with both tracers and the specificity was 80% with 99mTc-MIBI and 53% with 67Ga citrate. The positive predictive values were 85% and 68% and the negative predictive values were 59% and 44%, respectively. The signal-to-background ratio was 1.5 for 99mTc-MIBI and 2 for 67Ga citrate. At present, 99mTc-MIBI cannot replace 67Ga citrate in the assessment of lymphomas.

Somatostatin receptor imaging of small cell lung cancer (SCLC) by means of 111In-DTPA octreotide scintigraphy

Somatostatin receptors have been described on the membrane of neoplastic cells derived from the APUD system and their expression has also been demonstrated on small cell lung cancer (SCLC) in vitro and in vivo. 21 patients with SCLC were studied using 111In-octreotide (111In-OCT) scintigraphy. Scintigraphic examinations were performed following intravenous (i.v.) injection of 111 MBq 111In-OCT with whole-body scintigraphy and planar scintigraphy of the thorax as well as the SPET technique. No short-term side effects were described following 111In-OCT administration. We studied the 111In-OCT biodistribution in 3 patients with serial scintigraphies at 1, 5 and 24 h. We used the 5 h as standard scanning time for the following 18 patients. The scintigraphic results were compared with those of other conventional diagnostic procedures. 111In-OCT detected 86% (48/56) of the lesions already known at the time of scintigraphy. It was positive in all 20 SCLC patients and negative in one lung adenocarcinoma. 111In-OCT showed high sensitivity for mediastinal metastases (94%) and good sensitivity for bone metastases (75%) and abdominal lymph node metastases (71%). 111In-OCT did not detect two liver metastases. 111In-OCT detected five unknown lesions which were confirmed by other diagnostic examinations. 111In-OCT was also effective in cancer patients with low levels of NSE. Our study shows that 111In-OCT scintigraphy is a reliable, non-invasive technique to detect primary SLCL and its locoregional or distant metastases. The clinical utility of receptor status characterisation obtained with 111In-OCT scintigraphy should be evaluated by means of an appropriate prospective study.

Somatostatin receptor imaging. The presence of somatostatin receptors in rheumatoid arthritis

OBJECTIVE

To investigate the in vivo and in vitro expression of somatostatin receptors (SS-R) on synovial membranes of patients with rheumatoid arthritis (RA).

METHODS

The joints of 14 consecutive patients with active RA, 4 patients with severe osteoarthritis (OA), and 30 control patients were studied. The somatostatin analog [111In-DTPA-D-Phe1]-octreotide was used for in vivo SS-R scintigraphy, and the somatostatin analog [125I-Tyr3]-octreotide for in vitro SS-R autoradiography.

RESULTS

Seventy-six percent (220 of 290) of the painful joints and 76% (207 of 274) of the swollen joints of the patients with RA were visualized by SS-R scintigraphy. The degree of pain and swelling correlated well with positive scintigraphy findings in the joints (P < 0.0001). In 2 of the RA patients who underwent scintigraphy, as well as in 4 of 5 other patients, in vitro studies of the synovial membranes showed the presence of specific SS-R. In patients with OA, uptake of radioactivity in the affected joints was significantly lower than that in patients with RA. None of the joints of the control patients demonstrated uptake of radioactivity.

CONCLUSION

SS-R are present in the synovial tissue of patients with active RA, as demonstrated by both in vivo and in vitro techniques. The potential value of SS-R scintigraphy in the clinical evaluation of patients with active RA is presently unknown.

Expression of somatostatin receptors in normal, inflamed, and neoplastic human gastrointestinal tissues

The multiple actions of somatostatin are mediated by specific membrane-bound receptors present in all somatostatin target tissues, such as brain, pituitary, pancreas, gastrointestinal tract, and kidney. For instance, in the human gastrointestinal tract, three different types of tissue compartments express somatostatin receptors: the gastrointestinal mucosa, the peripheral nervous system, and the gut-associated lymphoid tissue, where the receptors are preferentially located in germinal centers. In all these cases, somatostatin binding is of high affinity and specific for bioactive somatostatin analogues. Somatostatin receptors are also expressed in pathological states, such as cancers. A particular abundance is found in neuroendocrine tumors of the gastrointestinal tract. Ninety percent of the carcinoids and a majority of islet cell carcinomas, including their metastases, usually have a high density of somatostatin receptors. Several different somatostatin-receptor subtypes can be expressed by these tumors, the SSTR2 subtype being the most frequently and abundantly expressed. The somatostatin receptors in tumors are identified with in vitro-binding methods, molecular biology techniques, or in vivo-imaging techniques; the latter allow the precise localization of the tumors and their metastases in the patients. Because somatostatin receptors in human gastroenteropancreatic tumors are functional, their identification can be used to predict the therapeutical efficacy of octreotide to inhibit excessive hormone release. Of differential diagnostic importance is the fact that other pathological processes in the gastrointestinal tract may be associated with a high density of somatostatin receptors. Ninety percent of lymphomas, including those with intestinal involvement express somatostatin receptors. Furthermore, a moderate number of colorectal carcinomas contain somatostatin receptors, whereas exocrine pancreatic carcinomas do not. Finally, an increased expression of SS receptors in nonneoplastic conditions, such as in intestinal veins in inflammatory bowel disease, has been recently observed. These observations demonstrate the ability of the human body to regulate SS receptors in a wide number of tissues and conditions.

Somatostatin analogue scintigraphy in granulomatous diseases

Normal as well as activated lymphocytes and macrophages have previously been shown by radioreceptor analysis to express somatostatin receptors (SS-R). The somatostatin (SS) analogue [111In-DTPA-D-Phe1]octreotide (111In-octreotide) is already used successfully in the visualization of a variety of neuro-endocrine tumours and malignant lymphomas. In the present study 20 consecutive patients were investigated, 12 with sarcoidosis, one with both sarcoidosis and aspergillosis, four with tuberculosis and three with Wegener's granulomatosis. For in vivo SS-R imaging, total-body scintigraphy was performed 24 and 48 h after the administration of 111In-octreotide. Granuloma localizations could be visualized in all patients studied; additional sites were found in nine patients with sarcoidosis and in two patients with tuberculosis. In vitro autoradiography of fresh tissue biopsies, using the SS analogue [125I-Tyr3]octreotide, showed binding at sites that were microscopically identified as granulomatous inflammation. These observations demonstrate the expression of SS-R by human granulomas. This scintigraphy procedure may contribute to a more precise staging and evaluation of granulomatous diseases, but more importantly it may be a sensitive indicator of the efficacy of glucocorticoid and/or immunosuppressive therapy.