Measurement of circulating transcripts and gene cluster analysis predicts and defines therapeutic efficacy of peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumors.

BACKGROUND: Peptide receptor radionuclide therapy (PRRT) is an effective method for treating neuroendocrine tumors (NETs). It is limited, however, in the prediction of individual tumor response and the precise and early identification of changes in tumor size. Currently, response prediction is based on somatostatin receptor expression and efficacy by morphological imaging and/or chromogranin A (CgA) measurement. The aim of this study was to assess the accuracy of circulating NET transcripts as a measure of PRRT efficacy, and moreover to identify prognostic gene clusters in pretreatment blood that could be interpolated with relevant clinical features in order to define a biological index for the tumor and a predictive quotient for PRRT efficacy. METHODS: NET patients (n = 54), M: F 37:17, median age 66, bronchial: n = 13, GEP-NET: n = 35, CUP: n = 6 were treated with (177)Lu-based-PRRT (cumulative activity: 6.5-27.8 GBq, median 18.5). At baseline: 47/54 low-grade (G1/G2; bronchial typical/atypical), 31/49 (18)FDG positive and 39/54 progressive. Disease status was assessed by RECIST1.1. Transcripts were measured by real-time quantitative reverse transcription PCR (qRT-PCR) and multianalyte algorithmic analysis (NETest); CgA by enzyme-linked immunosorbent assay (ELISA). Gene cluster (GC) derivations: regulatory network, protein:protein interactome analyses. STATISTICAL ANALYSES: chi-square, non-parametric measurements, multiple regression, receiver operating characteristic and Kaplan-Meier survival. RESULTS: The disease control rate was 72 %. Median PFS was not achieved (follow-up: 1-33 months, median: 16). Only grading was associated with response (p < 0.01). At baseline, 94 % of patients were NETest-positive, while CgA was elevated in 59 %. NETest accurately (89 %, χ(2) = 27.4; p = 1.2 × 10(-7)) correlated with treatment response, while CgA was 24 % accurate. Gene cluster expression (growth-factor signalome and metabolome) had an AUC of 0.74 ± 0.08 (z-statistic = 2.92, p < 0.004) for predicting response (76 % accuracy). Combination with grading reached an AUC: 0.90 ± 0.07, irrespective of tumor origin. Circulating transcripts correlated accurately (94 %) with PRRT responders (SD+PR+CR; 97 %) vs. non-responders (91 %). CONCLUSIONS: Blood NET transcript levels and the predictive quotient (circulating gene clusters+grading) accurately predicted PRRT efficacy. CgA was non-informative.

Gene transcript analysis blood values correlate with 68Ga-DOTA-somatostatin analog (SSA) PET/CT imaging in neuroendocrine tumors and can define disease status.

PURPOSE: Precise determination of neuroendocrine tumor (NET) disease status and response to therapy remains a rate-limiting concern for disease management. This reflects limitations in biomarker specificity and resolution capacity of imaging. In order to evaluate biomarker precision and identify if combinatorial blood molecular markers and imaging could provide added diagnostic value, we assessed the concordance between (68)Ga-somatostatin analog (SSA) positron emission tomography (PET), circulating NET gene transcripts (NETest), chromogranin A (CgA), and Ki-67 in NETs. METHODS: We utilized two independent patient groups with positive (68)Ga-SSA PET: data set 1 ((68)Ga-SSA PETs undertaken for peptide receptor radionuclide therapy (PRRT), as primary or salvage treatment, n = 27) and data set 2 ((68)Ga-SSA PETs performed in patients referred for initial disease staging or restaging after various therapies, n = 22). We examined the maximum standardized uptake value (SUVmax), circulating gene transcripts, CgA levels, and baseline Ki-67. Regression analyses, generalized linear modeling, and receiver-operating characteristic (ROC) analyses were undertaken to determine the strength of the relationships. RESULTS: SUVmax measured in two centers were mathematically evaluated (regression modeling) and determined to be comparable. Of 49 patients, 47 (96 %) exhibited a positive NETest. Twenty-six (54 %) had elevated CgA (χ(2) = 20.1, p < 2.5×10(-6)). The majority (78 %) had Ki-67 < 20 %. Gene transcript scores were predictive of imaging with >95 % concordance and significantly correlated with SUVmax (R (2) = 0.31, root-mean-square error = 9.4). The genes MORF4L2 and somatostatin receptors SSTR1, 3, and 5 exhibited the highest correlation with SUVmax. Progressive disease was identified by elevated levels of a quotient of MORF4L2 expression and SUVmax [ROC-derived AUC (R (2) = 0.7, p < 0.05)]. No statistical relationship was identified between CgA and Ki-67 and no relationship with imaging parameters was evident. CONCLUSION: (68)Ga-SSA PET imaging parameters (SUVmax) correlated with a circulating NET transcript signature. Disease status could be predicted by an elevated quotient of gene expression (MORF4L2) and SUVmax. These observations provide the basis for further exploration of strategies that combine imaging parameters and disease-specific molecular data for the improvement of NET management.

Evaluation of a new immunoassay for chromogranin A measurement on the Kryptor system.

BACKGROUND: Chromogranin A (CgA) is a biomarker for neuroendocrine tumors (NETs). The aims of this study were to evaluate differences in measurement between the ThermoFisher Brahms CgA Kryptor assay and the CisBio assay and to investigate the influence of patient covariates. Temperature stability of CgA using both assays was determined. DESIGN AND METHODS: 406 patients were analyzed for serum CgA using both assays. We performed a comparison study to determine whether several patient covariates (gender, use of protein pump inhibitors, impaired kidney function, referral department and tumor location) influenced the results. For the stability study, pooled serum samples were aliquoted and stored at different storage temperatures (room temperature, 4 °C and -20 °C) until assayed. In addition, 15 individual samples were evaluated after storage at 4 °C using the Kryptor assay. RESULTS: Differences in measured concentrations between the assays were statistically significant. Passing & Bablok fit showed ln Y(Kryptor)=1.05 ln X(CisBio) - 0.20 with a bias of 1.0% after logarithmic transformation. Patient covariates were not associated. Patients׳ sera showed variable stability for CgA in the Kryptor assay at room temperature and 4 °C, whereas the recovery in the CisBio assay was stable at both temperatures. CONCLUSION: Differences in measured CgA concentration between the assays could not be explained by the investigated patient covariates. Serum should be stored at -20 °C prior to determination using the Kryptor assay.

The peripheral blood compartment in patients with Graves' disease: activated T lymphocytes and increased transitional and pre-naive mature B lymphocytes.

Graves' disease (GD) is an autoimmune disease that involves aberrant B and T lymphocyte responses. Detailed knowledge about lymphocyte subpopulation composition will therefore enhance our understanding of the pathogenesis of GD and might support the development of new immunomodulatory treatment approaches. The aim of this study was to gain detailed insight into the composition of the peripheral blood lymphocyte compartment in GD before and during anti-thyroid drug therapy. Major B and T lymphocyte subpopulations were investigated by flow cytometry in peripheral blood from newly diagnosed GD patients (n = 5), GD patients treated with anti-thyroid drugs (n = 4), patients with recurrent GD (n = 7) and healthy controls (HC; n = 10). In GD patients, numbers of activated T lymphocytes [human leucocyte antigen D-related (HLA-DR)⁺ and CD25⁺] were increased. The B lymphocyte compartment in GD was characterized by significantly higher numbers of transitional (CD38(high) CD27⁻, P < 0.03) and pre-naive mature (CD38(low) CD27⁻ IgD⁺ CD5⁺, P < 0.04) B lymphocytes, while memory populations were slightly decreased. The increased numbers of CD5⁺, transitional and pre-naive mature B lymphocytes correlated positively with fT4 plasma levels. GD is associated with increased numbers of activated T lymphocytes and transitional and pre-naive mature CD5⁺ B lymphocytes within the peripheral blood. The increase in CD5⁺ B lymphocytes was due mainly to an increase in transitional and pre-naive mature B lymphocytes. Increased fT4 plasma levels might be associated with this increase in transitional and pre-naive mature CD5⁺ B lymphocytes.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours.

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.

Lutetium-labelled peptides for therapy of neuroendocrine tumours.

Treatment with radiolabelled somatostatin analogues is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumours. Symptomatic improvement may occur with (177)Lu-labelled somatostatin analogues that have been used for peptide receptor radionuclide therapy (PRRT). The results obtained with (177)Lu-[DOTA(0),Tyr(3)]octreotate (DOTATATE) are very encouraging in terms of tumour regression. Dosimetry studies with (177)Lu-DOTATATE as well as the limited side effects with additional cycles of (177)Lu-DOTATATE suggest that more cycles of (177)Lu-DOTATATE can be safely given. Also, if kidney-protective agents are used, the side effects of this therapy are few and mild and less than those from the use of (90)Y-[DOTA(0),Tyr(3)]octreotide (DOTATOC). Besides objective tumour responses, the median progression-free survival is more than 40 months. The patients' self-assessed quality of life increases significantly after treatment with (177)Lu-DOTATATE. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with (177)Lu-DOTATATE. These findings compare favourably with the limited number of alternative therapeutic approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable neuroendocrine tumours.

5-HIAA excretion is not associated with bone metabolism in carcinoid syndrome patients.

In patients with a carcinoid syndrome and neuroendocrine tumors of the digestive tract (carcinoids), elevated circulating serotonin (5-hydroxytryptamine, 5-HT) levels can be demonstrated. It can be hypothesized that bone metabolism will be affected in these patients, since serotonin receptors are expressed on bone cells and serotonin effects on bone have been demonstrated. However, to date, no data are available on bone metabolism parameters in patients with neuroendocrine tumors of the digestive tract (carcinoids). In the current retrospective study we have measured serum bone formation markers P1CP (pro-collagen type I C-terminal), and osteocalcin, and the bone resorption marker NTx (collagen breakdown product N-terminal), in a group of 61 carcinoid patients with increased circulating serotonin levels as demonstrated by increased excretion of the serotonin breakdown product, 5-hydroxy indole acetic acid (5-HIAA), in the urine (>50 µmol/24 h, so-called "hyper-secretors") and a control group of 23 carcinoid patients, without increased 5-HIAA excretion (so-called non-secretors). The 24-h urinary excretion of 5-HIAA reflects the 24-h production of serotonin. Measurements of markers of bone metabolism were performed in serum samples obtained before the start of medical treatment. The hypersecretor group had on average a 10-fold higher urinary 5-HIAA excretion than the control (non-secretor) group. No significant differences in bone metabolism parameters could be demonstrated between hyper-secretors and controls (non-secretors). Correlation and regression analyses could not demonstrate significant age- and sex-adjusted correlations between urinary 5-HIAA excretion and any of the markers for bone turnover. A limitation is that the exposure time to elevated levels of serotonin is unknown, which might have been too short to induce effects on bone metabolism. Treatment of human pre-osteoblasts SV-HFO with serotonin didn't change alkaline phosphatase activity throughout differentiation as well as mineralization. In conclusion, the current study in a unique group of untreated carcinoid patients could not demonstrate a major role for circulating serotonin in the control of bone metabolism.

Immunohistochemical localization and quantitative expression of somatostatin receptors in normal human spleen and thymus: Implications for the in vivo visualization during somatostatin receptor scintigraphy.

BACKGROUND: [111In-DTPA-D-Phe1]-octreotide scintigraphy allows the visualization of SRIF receptor (SSR)-expressing tumors, including thymic tumors, and normal tissues. While the spleen is clearly visualized, the thymus is not depicted, although both contain SSR. AIM: We evaluated whether the heterogeneity, the type, and the amount of SSR might explain this contrasting finding. MATERIALS, METHODS, AND RESULTS: By ligand-binding the number of [125I-Tyr11]-SRIF- 14 binding sites resulted comparable between the two tissues, whereas the number of [125I-Tyr3]-octreotide sites was significantly higher in the spleen (p<0.001). Quantitative RTPCR showed a significantly higher expression of sst2A mRNA in the spleen, whereas a significantly higher expression of SRIF and sst3 in the thymus. The highest density of sst2A in the spleen is in line with the in vivo uptake of [111In-DTPA-D-Phe1]- octreotide, which is considered a sst2-preferring ligand. The specificity is confirmed by the evidence that in vivo [111In-DTPA- D-Phe1]-octreotide uptake can be abolished during chronic administration of "cold" octreotide. Immunohistochemistry confirmed a preferential expression of sst2A on microenvironmental cells and of sst3 on lymphoid cells. CONCLUSIONS: The heterogeneity of SSR expression and the higher SRIF content explain the lack of thymus visualization during scintigraphy, whereas thymic tumors, which do not express SRIF, are visualized. Apart from the affinity of the radioligand, also the efficacy of the internalization is crucial for the in vivo uptake, and both heterogeneity and SRIF content affect this process. These observations might have an important impact when interpretating in vivo visualization of SSR-positive lesions, and when treatment with novel SRIF analogs is considered.

Improved control of severe hypoglycemia in patients with malignant insulinomas by peptide receptor radionuclide therapy.

CONTEXT: Insulinomas are relatively rare neuroendocrine tumors of the pancreas. Only 10% are considered malignant. Control of insulin hypersecretion and hypoglycemia in patients with malignant insulinomas may be extremely difficult. Different medications and chemotherapy schedules have been used. PATIENTS: Five patients with metastatic insulinomas and severe, poorly controllable, hypoglycemia are described. These patients required continuous glucose infusion to control severe hypoglycemia, which were induced by the high levels of insulin secretion. Conventional medications, such as diazoxide, or streptozotocin-based chemotherapies had been used to control hypoglycemia but were ineffective and/or produced adverse effects. All patients were treated with sc octreotide. INTERVENTION: Peptide receptor radionuclide therapy with radiolabeled-somatostatin analogs was used. RESULTS: After the start of radiolabeled somatostatin analog therapy, the five patients with metastatic insulinomas had stable disease for a mean period of 27 months. During these months, the patients were without any hypoglycemic episodes. Finally, three of five patients died because of progressive disease. CONCLUSIONS: Radiolabeled somatostatin analog therapy can stabilize tumor growth and can be very successful in further controlling severe hypoglycemia in malignant insulinomas. In our series, this eventually resulted in improved survival outside the hospital setting.

Radiolabelled regulatory peptides for imaging and therapy.

Radiolabelled peptides have shown to be an important class of radiopharmaceuticals for imaging and therapy of malignancies expressing receptors of regulatory peptides. These peptides have high affinity and specificity for their receptors. The majority of these receptors are present at different levels in different tissues and tumours. This review focuses on the application of regulatory peptides radiolabelled with (67/68)Ga, (90)Y, (111)In or (177)Lu. Due attention is given to the current status of research, limitations and future perspectives of the application of these radiolabelled peptides for imaging and radiotherapy. It also covers elements of the basic science and preclinical and clinical aspects in general, however, mostly based on somatostatin receptor-mediated imaging and therapy. New analogues, chelators, radionuclides and combinations thereof are discussed.

Practical aspects of peptide receptor radionuclide therapy with [177Lu][DOTA0, Tyr3]octreotate.

Lutetium-177 is increasingly used in patients for receptor-targeted radionuclide therapy with peptides such as [DOTA0,Tyr3]octreotate. In our therapy facility, we are performing yearly 400 treatments with each 7.4 GBq [177Lu][DOTA0,Tyr3]octreotate. Finger dosimetry data during radiolabeling reveal higher doses on the right hands of right-handed workers with the highest equivalent dose for the middle finger (53+/-12 microSv/GBq). Extrapolating dosimetry data, assuming 400 doses of 7.4 GBq per year performed by 4 workers, result in a mean equivalent dose of 23+/-11 mSv and 14+/-6 mSv for finger top and ring dose, respectively. Preparation of 400 doses will result in an effective dose of 0.5-1.5 mSv per year for these 4 workers. The extra radiation dose for workers during the radiolabeling of these doses thus remains below 10% of the legal annual limits, which is in accordance with the ALARA optimization principle. Based on measurements of the maximal radiation level at 1 m distance (7.5+/-3.6 microSv/h), patients treated with 7.4 GBq [177Lu][DOTA0,Tyr3]octreotate can already leave the therapy facility the next day. As radioactive waste streams are based on the half-lives of the used radionuclides, 177Lu-waste (t1/2=6.7 d) was initially collected along with the 131I-waste (t1/2=8 d). According to both manufacturers' specifications, 177Lu contains less than 0.4 kBq 177mLu/MBq 177Lu (at the end of neutron irradiation), when produced by the [176Lu n, gamma 177Lu] reaction via thermal neutron bombardment of enriched lutetium oxide. Unfortunately, because of the huge amounts of 177Lu used, contaminating 177mLu turned out to prevent the quick discharge of this waste, for some containers even after some years of storage. Therefore, a technique for calibrating 177mLu was developed, simultaneously confirming the manufacturer's specifications on the presence of 177mLu in 177Lu. Subsequently a reliable technique was developed to measure 177mLu in waste containers using a beta/gamma-contamination monitor. It is advised to collect 177mLu/177Lu-waste and certainly high-activity lutetium waste separated from 131I according the regulations in the country of use. Apart from the mentioned waste, excreta from patients are collected in decay tanks, where they are stored for 1-2 months before they are discarded into the general sewer within the overall tolerated discharge limit (150 radiotoxicity equivalents/year for our department).

Comparison of [(177)Lu-DOTA(0),Tyr(3)]octreotate and [(177)Lu-DOTA(0),Tyr(3)]octreotide: which peptide is preferable for PRRT?

PURPOSE: Patients with somatostatin receptor subtype 2-positive metastasised neuroendocrine tumours can be treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [(177)Lu-DOTA(0),Tyr(3)]octreotide ((177)Lu-DOTATOC) and [(177)Lu-DOTA(0),Tyr(3)]octreotate ((177)Lu-DOTATATE), to see which peptide should be preferred for PRRT with (177)Lu. METHODS: In the same patients, 3,700 MBq (177)Lu-DOTATOC and 3,700 MBq (177)Lu-DOTATATE was administered in separate therapy sessions. Amino acids were co-administered. Whole-body scanning was performed on days 1, 4 and 7 post therapy. Blood and urine samples were collected. We calculated residence times for tumours, spleen and kidneys. RESULTS: All patients had longer residence times in spleen, kidneys and tumours after use of (177)Lu-DOTATATE (p=0.016 in each case). Comparing (177)Lu-DOTATATE with (177)Lu-DOTATOC, the mean residence time ratio was 2.1 for tumour, 1.5 for spleen and 1.4 for kidneys. Dose-limiting factors for PRRT are bone marrow and/or kidney dose. Although the residence time for kidneys was longer when using (177)Lu-DOTATATE, the mean administered dose to tumours would still be advantageous by a factor of 1.5, assuming a fixed maximum kidney dose is reached. Plasma radioactivity after (177)Lu-DOTATATE was comparable to that after (177)Lu-DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for (177)Lu-DOTATOC. CONCLUSION: (177)Lu-DOTATATE had a longer tumour residence time than (177)Lu-DOTATOC. Despite a longer residence time in kidneys after (177)Lu-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.

Neuroendocrine tumors and somatostatin: imaging techniques.

Tumors and metastases bearing the somatostatin receptor subtypes 2 (SSTR2) or SSTR5 can be visualized in vivo after injection of radiolabeled octapeptide somatostatin analogs like 111In-pentetreotide. The sensitivity of 111In-pentetreotide scintigraphy for the detection of carcinoid tumors is 86-95%. The sensitivity of 111In-pentetreotide scintigraphy for the detection of gastrinomas, vasoactive intestinal polypeptide-secreting tumors, and glucagonomas as well as clinically non-functioning lesions is 75-100%. However, for insulinoma this is 50-60%. 111In-pentetreotide scintigraphy generally has a lower detection rate for benign pheochromocytomas than 123I-MIBG scintigraphy, but it can have a complementary role for the staging of malignant pheochromocytomas. It can also be used for the detection of extra-adrenal pheochromocytomas and paragangliomas. Most GH- and TSH-secreting pituitary adenomas can be visualized using 111In-pentetreotide. 111In-pentetreotide scintigraphy is negative in microprolactinomas and ACTH-secreting pituitary microadenomas. 111In-pentetreotide scintigraphy has been successful for the localization of extra-pituitary ACTH-secreting tumors and their metastases, and especially for occult tumors. A large variety of lesions in and around the pituitary region express somatostatin receptors and, therefore, can be visualized by 111In-pentetreotide scintigraphy.

Molecular radiotherapy with somatostatin analogs for (neuro-)endocrine tumors.

Peptide receptor radionuclide therapy (PRRT) holds great promise for the future regarding the treatment of various cancers. With the use of radiolabelled peptides, which bind with high affinity to their receptors on cancer cells, it is possible to target the cancer efficiently. In gastroenteropancreatic tumors, radiolabelled somatostatin analog therapy has proven to be effective. Dose-limiting organs are the bone marrow and the kidneys. With the currently used dose schemes and kidney protection, PRRT is relatively safe and serious side-effecs are rare. Which radiolabelled somatostatin analog can be regarded as the most effective therapy cannot be concluded from the available literature. Also, the development of therapy strategies with combinations of different radionuclides and or peptides is of interest as these strategies may provide an increase in therapeutic efficacy in the future.

Treatment of patients with gastro-entero-pancreatic (GEP) tumours with the novel radiolabelled somatostatin analogue [177Lu-DOTA(0),Tyr3]octreotate.

Medical treatment and chemotherapy are seldom successful in achieving objective tumour reduction in patients with metastatic neuroendocrine tumours. Treatment with the radiolabelled somatostatin analogue [(90)Y-DOTA(0),Tyr(3)]octreotide may result in partial remissions in 10-25% of patients. The newer analogue [DOTA(0),Tyr(3)]octreotate (octreotate) has a ninefold higher affinity for the somatostatin receptor subtype 2 as compared with [DOTA(0),Tyr(3)]octreotide. Also, labelled with the beta- and gamma-emitting radionuclide (177)Lu, it has proved very successful in achieving tumour regression in animal models. The effects of (177)Lu-octreotate therapy were studied in 35 patients with neuroendocrine gastro-entero-pancreatic (GEP) tumours who underwent follow-up for 3-6 months after receiving their final dose. Patients were treated with doses of 100, 150 or 200 mCi (177)Lu-octreotate, to a final cumulative dose of 600-800 mCi, with treatment intervals of 6-9 weeks. Nausea and vomiting within the first 24 h after administration were present in 30% and 14% of the administrations, respectively. WHO toxicity grade 3 anaemia, leucocytopenia and thrombocytopenia occurred after 0%, 1% and 1% of the administrations, respectively. Serum creatinine and creatinine clearance did not change significantly. The effects of the therapy on tumour size were evaluable in 34 patients. Three months after the final administration, complete remission was found in one patient (3%), partial remission in 12 (35%), stable disease in 14 (41%) and progressive disease in seven (21%), including three patients who died during the treatment period. Tumour response was positively correlated with a high uptake on the octreoscan, limited hepatic tumour mass and a high Karnofsky Performance Score. Because of the limited efficacy of alternative therapies, many physicians currently adopt an expectant attitude when dealing with patients with metastatic GEP tumours. However, in view of the high success rate of therapy with (177)Lu-octreotate and the absence of serious side-effects, we advocate its use in patients with GEP tumours without waiting for tumour progression.

[177Lu-DOTAOTyr3]octreotate: comparison with [111In-DTPAo]octreotide in patients.

The somatostatin analogue [DOTA0,Tyr3]octreotate has a nine-fold higher affinity for the somatostatin receptor subtype 2 as compared with [DOTA0, Tyr3]octreotide. Also, labelled with the beta- and gamma-emitting radionuclide lutetium-177, this compound has been shown to have a very favourable impact on tumour regression and animal survival in a rat model. Because of these reported advantages over the analogues currently used for somatostatin receptor-mediated radiotherapy, we decided to compare [177Lu-DOTA0,Tyr3]octreotate (177Lu-octreotate) with [111In-DTPA0]octreotide (111In-octreotide) in six patients with somatostatin receptor-positive tumours. Plasma radioactivity after 177Lu-octreotate expressed as a percentage of the injected dose was comparable with that after 111In-octreotide. Urinary excretion of radioactivity was significantly lower than after 111In-octreotide, averaging 64% after 24 h. The uptake after 24 h, expressed as a percentage of the injected dose of 177Lu-octreotate, was comparable to that after 111In-octreotide for kidneys, spleen and liver, but was three- to fourfold higher for four of five tumours. The spleen and kidneys received the highest absorbed doses. The doses to the kidneys were reduced by a mean of 47% after co-infusion of amino acids. It is concluded that in comparison with the radionuclide-coupled somatostatin analogues that are currently available for somatostatin receptor-mediated radiotherapy, 177Lu-octreotate potentially represents an important improvement. Higher absorbed doses can be achieved to most tumours, with about equal doses to potentially dose-limiting organs; furthermore, the lower tissue penetration range of 177Lu as compared with 90Y may be especially important for small tumours.

Somatostatin receptor-mediated imaging and therapy: basic science, current knowledge, limitations and future perspectives.

In vivo somatostatin receptor-mediated scintigraphy has proven to be a valuable method for the visualisation of neuroendocrine tumours and their metastases. A new application is the use of radiolabelled analogues for somatostatin receptor-mediated therapy. This paper presents a review on the basic science, historical background and current knowledge of somatostatin receptor subtypes and their expression in neuroendocrine tumours. New somatostatin analogues, new chelators, "new" radionuclides and combinations thereof are also discussed. Due attention is given to limitations and future perspectives of somatostatin receptor-mediated imaging and therapy.

In vivo and in vitro expression of somatostatin receptors in two human thymomas with similar clinical presentation and different histological features.

[(111)In-DTPA0]octreotide scintigraphy allows the in vivo visualization of several types of SS receptor (SSR)-expressing tumors. Among these, thymomas have been recently detected. Here we report on 2 patients admitted for myasthenia gravis and radiological evidence of thymic mass. Although these patients had similar clinical presentation, in vivo SSR scintigraphy displayed a difference in the degree of the [(111)In-DTPA0]octreotide uptake. Considering that both thymic masses had comparable volume, [(111)In-DTPA0]octreotide level was significantly higher in one of the 2 tumors (tumor/background ratio of 5.7 vs 2.6). The SSR subtype expression pattern was studied in vitro on the surgically resected specimens by ligand binding techniques, quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. According to the recent World Health Organization classification, the 2 tumors were classified A and B2 thymomas respectively. In membrane homogenates, we found a higher number of high affinity [125I-Tyr11]-SS-14 binding sites in the B2 thymomas (23.5+/-2.5 vs 12.0+/-0.4 fmol/mg membrane protein; p<0.05). RT-PCR analysis showed sst1, sst2A and sst3 mRNA in the 2 thymoma tissues, whereas SS mRNA was detectable only in the A thymoma. Quantitative evaluation of RT-PCR data showed a comparable expression of the relative amount of sst2A mRNA in both tumors, whereas a significant higher expression of sst3 mRNA in the B2 thymoma. Sst2A immunoreactivity was localized mainly on the endothelium of intratumoral vessels, whereas sst3 was present on either tumoral epithelial cells or normal reactive thymocytes. The expression of sst2A receptors in these tumors is in line with the in vivo visualization by [(111)In-DTPA0]octreotide, which is considered a sst2-preferring ligand. However, since radioligand uptake was significantly higher in the B2 thymoma, which expressed the largest sst3 mRNA levels, it might be possible that this subtype is involved in determining the tumor visualization during SSR scintigraphy. Apart from the affinity of the radioligand for the receptor, also the efficacy of the internalization of the radioligand-receptor complex might play a role in radioactivity accumulation during in vivo SSR scintigraphy. In fact, although octreotide binds with lower affinity to sst3 receptors, this subtype displayed the highest amount of agonist-dependent receptor internalization compared to the other SSR subtypes. Moreover, sst3 was localized on both tumor cells and reactive thymocytes, and these latter cells are characterized by a very active turnover of membrane molecules. Finally, although more cases need to be evaluated, the lack of detection of SS mRNA in the tumor presenting a more aggressive phenotype (B2 thymoma) might have physiopathological or prognostic significance.

Somatostatin receptor scintigraphy in the follow-up of patients with differentiated thyroid cancer.

UNLABELLED: The aim of this study was to compare the results of somatostatin receptor scintigraphy (SRS) and of radioiodine scintigraphy in patients with metastatic differentiated thyroid carcinoma during L-thyroxine suppression therapy and after withdrawal. Twenty-five patients were studied: 16 patients had papillary cancer and 12 of them had metastatic disease; 9 patients had follicular cancer and 7 of these had known metastases. In 7 patients SRS was performed during thyroxine withdrawal, in 12 during thyroxine therapy within 9 months from radioiodine scintigraphy, in 6 others both during suppression therapy and after withdrawal. SRS was positive in 18 of 25 (72%) patients. It demonstrated lesions in 11 of 13 (85%) patients after thyroxine withdrawal and in 12 of 18 (67%) patients during thyroxine suppression. In 6 patients in whom a direct comparison was made before and after withdrawal, essentially the same information was obtained. Six of 8 (75%) patients with lesions that did not concentrate radioiodine showed uptake of labeled octreotide in these lesions. In 5 of 17 (29%) patients whose tumors concentrated radioiodine, no uptake was found during SRS. CONCLUSIONS: 1) in patients with metastatic differentiated thyroid carcinoma, tumor sites can be visualized using SRS; 2) there is no need to withdraw patients from suppression therapy in order to perform SRS; 3) in some patients whose lesions do concentrate labeled octreotide but not radioiodine, the use of somatostatin analogues labeled with (111)In or [90Y] can provide new therapeutic options.