Somatostatin receptors: from basic science to clinical approach--thyroid

Comparative evaluation of somatostatin and CXCR4 receptor expression in different types of thyroid carcinoma using well-characterised monoclonal antibodies

Background

Papillary and follicular thyroid carcinomas can be treated surgically and with radioiodine therapy, whereas therapeutic options for advanced stage IV medullary and for anaplastic tumours are limited. Recently, somatostatin receptors (SSTs) and the chemokine receptor CXCR4 have been evaluated for the treatment of thyroid carcinomas, however, with contradictory results.

Methods

The expression of the five SSTs and of CXCR4 was assessed in 90 samples from 56 patients with follicular, papillary, medullary, or anaplastic thyroid carcinoma by means of immunohistochemistry using well-characterised monoclonal antibodies. The stainings were evaluated using the Immunoreactivity Score (IRS) and correlated to clinical data. In order to further substantiate the immunohistochemistry results, in serial sections of a subset of the samples receptor expression was additionally examined at the mRNA level using qRT-PCR.

Results

Overall, SST and CXCR4 protein expression was low in all four entities. In single cases, however, very high IRS values for SST2 and CXCR4 were observed. SST2 was the most frequently expressed receptor, found in 38% of cases, followed by SST5 and SST4, found in 14 and 9% of tumours, respectively. SST1 and SST3 could not be detected to any significant extent. CXCR4 was present in 12.5% of medullary and 25% of anaplastic carcinomas. Expression SST3, SST4, SST5 and CXCR4 was positively correlated with expression of the proliferation marker Ki-67. Additionally, a negative interrelationship between SST4 or SST5 expression and patient survival and a positive association between SST3 expression and tumour diameter were observed. qRT-PCR revealed a similar receptor expression pattern to that seen at the protein level. However, probably due to the low overall expression, no correlation was found for the SSTs or the CXCR4 between the IRS and the mRNA values.

Conclusions

SST- or CXCR4-based diagnostics or therapy in thyroid carcinomas should not be considered in general but may be feasible in single cases with high levels of expression of these receptors.

Lateral ectopic thyroid mimics carotid body tumor on Indium-111 pentetreotide scintigraphy

A 34-year old woman with past history of anxiety, depression, and hypothyroidism resulting from prior total thyroidectomy for multinodular goiter presented with complaints of palpitations, sweating, and tachycardia. Clinical examination revealed a painless right lateral neck mass. USG/CT of the neck revealed the soft tissue mass located at the right carotid bifurcation. A subsequent Indium-111 pentetreotide somatostatin receptor scintigraphy (SRS) demonstrated tracer uptake in the mass. Hence, secretory carotid body tumor/paraganglioma was strongly suspected. However, post-surgical histopathological specimen revealed only benign thyroid follicles indicative of lateral ectopic thyroid with no evidence of neuroendocrine cells or malignancy. This case highlights the importance of considering lateral ectopic thyroid, a very rare entity, in the differential diagnosis for carotid bifurcation masses. Also highlighted is the false positivity from normal but ectopic thyroid tissue on Indium-111 pentetreotide SRS mimicking a paraganglioma.

SSTR2A expression in medullary thyroid carcinoma is correlated with longer survival

PURPOSE

Medullary thyroid carcinoma (MTC) derives from the parafollicular C-cells of the thyroid gland. Somatostatin receptors (SSTRs) are expressed in various neuroendocrine tumours including MTC. The aim of this study was to evaluate SSTR2A as a prognostic factor for MTC, to study distribution of SSTR2A expression within tumours and to compare expression of SSTR2A between primary tumours and corresponding lymph node metastases.

METHODS

Patients who underwent surgery between 1988 and 2014 for MTC from five tertiary referral centres in The Netherlands were included. In total, primary tumours of 114 patients and lymph node metastases of 34 patients were analysed for expression of SSTR2A using a tissue microarray, and correlated with clinicopathological variables and survival.

RESULTS

The mean age of patients was 45.5 years (SD 16.2), 55 patients were male (49.5%). Primary tumours of 58 patients (50.9%) showed SSTR2A expression. In multivariate Cox-regression analysis, SSTR2A positivity correlated independently with better overall survival (OS) (HR 0.3; 95% CI 0.1-1.0). In stage IV MTC patients, 10-year survival rates for SSTR2A-negative and positive patients were 43% and 96%, respectively. In 53.9% of patients with lymph node metastases, expression in primary tumour and lymph node metastases differed.

CONCLUSION

SSTR2A expression is correlated with longer OS in MTC, especially for stage IV patients, suggesting that SSTR2A expression might be a useful prognostic factor in MTC. The SSTR2A status of the primary MTC does not predict expression in lymph node metastases.

Update on the role of somatostatin analogs for the treatment of patients with gastroenteropancreatic neuroendocrine tumors

Somatostatin analogs (SA) are the standard of care for controlling symptoms of patients with functional gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs). SA control symptoms in more than 70% of patients with carcinoid syndrome. Similar results are obtained in patients with functional, hormone-secreting, pancreatic NETs. The use of SA as antiproliferative agents has been established only recently. Retrospective studies have shown stabilization of tumor growth in >50% of patients with progressive disease. The results of a recent randomized phase III trial (PROMID) demonstrated that the median time to progression in patients with midgut carcinoid tumors treated with octreotide LAR (Long-Acting-Repeatable, Novartis, Basel, Switzerland) was more than twice as long compared to that of patients treated with placebo. The results of a phase III study of lanreotide versus placebo in nonfunctional NETs are not yet available. More studies are needed to determine whether combining SA with novel targeted treatments will result in enhanced antiproliferative activity compared to treatment with a SA alone. Studies are ongoing using pan-receptor agonists (eg, pasireotide) and chimeric dimers, which possess features of somatostatin and dopamine agonists (dopastatins) and are thought to enhance symptom control by binding multiple receptors (somatostatin and dopamine receptors). Somatostatin receptor antagonists are also currently being developed for clinical use. Peptide receptor radionuclide therapy (PRRT), consisting of yttrium-90 and lutetium-177 isotopes conjugated with SA appear to be efficacious in advanced NETs. Randomized studies are needed to definitively establish the safety and efficacy of this strategy compared to other available treatments, and to determine which radiolabeled isotopes or combinations are most effective.

Immunohistochemical expression and localization of somatostatin receptor subtypes in androgen ablated prostate cancer

OBJECTIVE

The aim was to examine the expression and localization of the five somatostatin receptors (termed SSTR1 to 5) in radical prostatectomies (RPs) from patients with prostatic adenocarcinoma (PCa) under complete androgen ablation (CAA) before operation.

MATERIAL

The five SSTRs were evaluated in the epithelial, smooth muscle and endothelial cells of normal-looking epithelium (Nep), high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa in 20 RPs with clinically detected PCa from patients under CAA. Twenty RPs with clinically detected PCa from hormonally untreated patients were used as control group.

RESULTS

Concerning the secretory cells (i) Membrane staining was seen for SSTR3 and SSTR4; the mean percentages of positive cells, higher in SSTR3 than in SSTR4, decreased sharply in HGPIN and PCa compared with Nep; the mean percentages in the androgen ablated group were 30% to 90% lower than in the untreated; (ii) Cytoplasmic staining was seen for all five SSTRs; the mean percentages of positive cells in Nep, HGPIN and PCa of the untreated group were similar, and in general as high as 80% or more; in the treated group, the Nep values were similar to those in the untreated, whereas the values in HGPIN and PCa were lower for SSTR1, three and five, with a decrease of 30% for SSTR1; (iii) Nuclear staining was seen with SSTR4 and SSTR5, the mean percentages for the former being much lower than for the latter; treatment affected both HGPIN and PCa, whose proportions of stained cells were 30% to 55% lower than in the untreated group. Cytoplasmic staining in the basal cells was seen for all five SSTRs, both in Nep and HGPIN. The values in the treated group were lower than in the other, the difference between the two group being in general comprised between 10% and 40%. Treatment did not affect SSTR staining in the smooth muscle and endothelial cells.

CONCLUSIONS

The present study expands our knowledge on the expression and localization of the five SSTRs in the prostate following CAA.

Somatostatin receptor subtypes in hormone-refractory (castration-resistant) prostatic carcinoma

The aim of this study was to examine the tissue expression and localisation of the somatostatin receptors (SSTRs) in hormone-refractory (HR) prostate cancer (PCa). Five SSTRs were evaluated immunohistochemically in 20 radical prostatectomies (RPs) with Gleason score (GS) 3+3=6 PCa, in 20 RPs with GS 4+4=8 and 4+5=9 PCa, and 20 transurethral resection of the prostate specimens with HR PCa. The mean values in the cytoplasm (all five SSTRs were expressed), membrane (only SSTR3 and SSTR4 were expressed) and nuclei (only SSTR4 and SSTR5 were expressed) of the glands in HR PCa were 20-70% lower than in the other two groups, the differences being statistically significant. All five SSTRs were expressed in the smooth muscle and endothelial cells of HR PCa, the mean values being lower than in the other two groups. In conclusion, this study expands our knowledge on the expression and localisation of five SSTRs in the various tissue components in the HR PCa compared with hormone-sensitive PCa.

Somatostatin receptor 2 expression determined by immunohistochemistry in cold thyroid nodules exceeds that of hot thyroid nodules, papillary thyroid carcinoma, and Graves' disease

BACKGROUND

There is a plethora of partly contradictory reports on somatostatin receptor (SSTR) expression in thyroid tumors. Therefore, our goal was to systematically determine SSTR2 expression in benign cold thyroid nodules (CNs), hot thyroid nodules (HNs), papillary carcinomas (PCs), and Graves' disease (GD) in comparison with intraindividual control tissues by means of immunohistochemistry.

METHODS

Tissue sections from 19 HNs, 10 CNs, 17 PCs and their surrounding tissues, and 8 GD thyroids were immunostained for SSTR2. Membranous SSTR2 staining was quantitated by evaluating 10 high-power fields (HPFs) systematically distributed along the largest diameter of the tissue section.

RESULTS

The area covered by thyroid epithelial cells in 10 HPFs expressed as median (in mm(2)) was 0.53 for CNs, 0.44 for HNs, 1.5 for PCs, 1.3 for GD, and 0.3 for the surrounding tissues. The SSTR2 staining density determined by dividing the area of SSTR2 positively stained thyroid epithelial cells (in mm(2)) by the area of all thyroid epithelial cells (in mm(2)) in 10 HPFs was 0.1662 for CNs, 0.0204 for HNs, 0.0369 for PCs, and 0.0386 for GD.

CONCLUSIONS

SSTR2 expression is inhomogeneous in thyroid disease, with the highest density detected in CNs. It remains to be determined whether this finding could be of pathophysiologic or therapeutic relevance. The high SSTR2 density in CNs should be considered in the interpretation of SSTR scintigraphy-positive findings.

Effects of therapy with [177Lu-DOTA 0,Tyr 3]octreotate on endocrine function

Purpose

Peptide receptor radionuclide therapy (PRRT) with radiolabelled somatostatin analogues is a novel therapy for patients with somatostatin receptor-positive tumours. We determined the effects of PRRT with [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate (¹⁷⁷Lu-octreotate) on glucose homeostasis and the pituitary-gonadal, pituitary-thyroid and pituitary-adrenal axes.

Methods

Hormone levels were measured and adrenal function assessed at baseline and up to 24 months of follow-up.

Results

In 35 men, mean serum inhibin B levels were decreased at 3 months post-therapy (205 ± 16 to 25 ± 4 ng/l, p < 0.05) and follicle-stimulating hormone (FSH) levels increased (5.9 ± 0.5 to 22.7 ± 1.4 IU/l, p < 0.05). These levels returned to near baseline levels. Total testosterone and sex hormone binding globulin (SHBG) levels decreased (15.0 ± 0.9 to 10.6 ± 1.0 nmol/l, p < 0.05 and 61.8 ± 8.7 to 33.2 ± 3.7 nmol, p < 0.05), respectively, whereas non-SHBG-bound T did not change. An increase (5.2 ± 0.6 to 7.7 ± 0.7 IU/l, p < 0.05) of luteinizing hormone (LH) levels was found at 3 months of follow-up returning to baseline levels thereafter. In 21 postmenopausal women, a decrease in levels of FSH (74.4 ± 5.6 to 62.4 ± 7.7 IU/l, p < 0.05) and LH (26.8 ± 2.1 to 21.1 ± 3.0 IU/l, p < 0.05) was found. Of 66 patients, 2 developed persistent primary hypothyroidism. Free thyroxine (FT₄) levels decreased (17.7 ± 0.4 to 15.6 ± 0.6 pmol/l, p < 0.05), whereas thyroid-stimulating hormone (TSH) and triiodothyronine (T₃) levels did not change. Reverse triiodothyronine (rT₃) levels decreased (0.38 ± 0.03 to 0.30 ± 0.01 nmol/l, p < 0.05). Before and after therapy adrenocorticotropic hormone (ACTH) stimulation tests showed an adequate response of serum cortisol (> 550 nmol/l, n = 18). Five patients developed elevated HbA_1c levels (> 6.5%).

Conclusion

In men ¹⁷⁷Lu-octreotate therapy induced transient inhibitory effects on spermatogenesis, but non-SHBG-bound T levels remained unaffected. In the long term, gonadotropin levels decreased significantly in postmenopausal women. Only a few patients developed hypothyroidism or elevated levels of HbA_1c. Therefore, PRRT with ¹⁷⁷Lu-octreotate can be regarded as a safe treatment modality with respect to short- and long-term endocrine function.

Is there a role for sandostatin treatment in patients with progressive thyroid cancer and iodine-negative but somatostatin-receptor-positive metastases?

INTRODUCTION

The aim of our study was to determine whether treatment with a long-acting somatostatin-receptor analogue is effective in patients with (131)I-negative but somatostatin-receptor-positive metastases from dedifferentiated and anaplastic thyroid cancer.

MATERIALS AND METHODS

Twelve patients were screened for the study. All of them showed progressive disease confirmed by radiologic evaluation, increasing serum thyroglobulin (Tg), and negative diagnostic or posttherapeutic (131)I whole-body scans (WBS). Eight of 12 patients (4 males and 4 females; age range, 57-89 years; 1 papillary thyroid cancer; 4 poorly differentiated follicular thyroid cancer; 1 follicular and anaplastic thyroid cancer; 2 anaplastic thyroid cancer) showed positive somatosatin-receptor expression in Tc-99m depreotide WBS/SPECT (Tc-99m Dep.WBS). Initially, in all patients fluorine-18 2-fluoro-2- D-glucose-positron emission tomography-computed tomography ((18)F-FDG-PET-CT), Tc-99m Dep.WBS, and Tg measurements were performed. In the case of positive receptor scintigraphy, patients were treated with 20mg Sandostatin LAR (Novartis Pharmaceuticals, Basel, Switzerland) once per month intramuscularly over a period of 6 months followed by repeated (18)F-FDG-PET-CT, Tc-99m Dep.WBS, and Tg measurement to determine metabolic activity and tumor size. In case of tumor progression, the dose was increased to 30mg of Sandostatin LAR once per month.

RESULTS

Only 3 patients were able to undergo long-term treatment. Two patients were treated with octreotide long-acting release (LAR) for 1 year and 1 patient for 1(1/2) years. All patients showed progressive disease during the treatment: an increase of serum Tg on one hand and an increase in the number of lesions and extent in tumor size visible on FDG-PET-CT and Tc-99m Dep.WBS on the other. During the treatment there was no change in receptor expression, nevertheless, clear tumor progression under therapy with a somatostatin analogue was visible in FDG-PET-CT and in Tc-99m Dep.WBS.

CONCLUSION

Our data demonstrate that all of our patients treated with a somatostatin analogue showed clinical progression and that our attempt to achieve a stabilization of the disease failed.