Elsevier

Human Pathology

Volume 46, Issue 3, March 2015, Pages 390-396
Human Pathology

Original contribution
Increased SSTR2A and SSTR3 expression in succinate dehydrogenase–deficient pheochromocytomas and paragangliomas,☆☆

https://doi.org/10.1016/j.humpath.2014.11.012Get rights and content

Summary

Many neuroendocrine tumors, including pheochromocytomas (PCs) and paragangliomas (PGLs), express one or more somatostatin receptors (SSTR1-5). A number of studies have reported SSTR expression in PCs and PGLs. However, receptor expression patterns have been conflicting, and until recently, specific monoclonal antibodies were not available against SSTR1-5. The aim of this study was to compare SSTR1-5 expression in succinate dehydrogenase (SDH)–deficient PCs and PGLs (defined as having absent SDHB immunostaining) to those tumors with normal SDHB staining. Immunohistochemistry for SDHB and SSTR1-5 was performed using specific monoclonal antibodies on archived formalin-fixed, paraffin-embedded tissue from patients who had undergone surgery for PC or PGLs. A total of 182 PC/PGLs were included (129 adrenal, 44 extra-adrenal, 9 metastases); 32 tumors were SDH deficient, whereas 150 tumors had positive SDHB staining. SDH-deficient tumors were more likely to demonstrate moderate or strong staining for SSTR2A and SSTR3 when compared with SDH-sufficient tumors (91% versus 49% [P < .0001] and 50% versus 21% [P = .0008], respectively). Immunostaining for the other SSTRs was not different between SDH-deficient and tumors with preserved SDHB staining. SSTR2A and SSTR3 are more likely to be expressed in SDH-deficient PC/PGLs as compared with tumors demonstrating normal SDHB staining pattern. These findings suggest that the role of somatostatin analogue therapy (unlabeled or radiolabeled) should be reexamined in the context of the underlying SDHB immunohistochemistry pattern.

Introduction

Pheochromocytomas (PCs) and paragangliomas (PGLs) are rare catecholamine-producing tumors arising from chromaffin cells in the adrenal glands or extraadrenal neural crest tissue. These catecholamine-secreting tumors are frequently hereditary, resulting from germline mutations in various tumor predisposition genes. Of these genes, succinate dehydrogenase subunit B (SDHB) is of particular interest due to increased malignant potential of associated PC/PGLs (metastatic rate of 30% versus 10% of all PC/PGLs) [1]. Determining whether PC/PGLs are benign or malignant in the absence of metastatic disease is limited by lack of reliable criteria to predict malignant behavior. Currently, the only effective treatment of PC/PGLs is surgery. Patients with inoperable malignant PC/PGLs may die of metastatic disease or from complications due to excess catecholamine production such as sudden death or heart failure. Nonsurgical treatment options for malignant disease are limited, and there is a lack of survival data available from randomized controlled trials using chemotherapy and radiolabeled therapies [2], [3], [4], in part resulting from the rarity of these tumors. Improved understanding of the biology of SDHB-associated and/or malignant PC/PGLs would assist in identifying new nonsurgical therapies.

Many neuroendocrine tumors, including PC/PGLs, express one or more somatostatin receptor subtypes (SSTR1-5). Somatostatin is a neuropeptide with affinity for all 5 receptor subtypes and can inhibit both hormone secretion and cell proliferation. Analogues of somatostatin (octreotide, octreotide LAR, and lanreotide) demonstrate high affinity for SSTR2 and, to a lesser extent, SSTR5. Although they are very successfully used in the treatment of some tumors types, such as SSTR2-expressing growth hormone–secreting pituitary tumors, and have been demonstrated to not only control symptoms but also increase progression-free survival in patients with metastatic small intestinal neuroendocrine tumors [5], [6], treatment for patients with chromaffin cell tumors has been variable and overall disappointing [7], [8], [9], [10], [11], [12], [13].

A number of studies have assessed SSTR subtypes in PC/PGL [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. Results have been conflicting as to the frequency of receptor subtype expression. Although SSTR3 has been detected in most tumors studied, SSTR2A expression has varied from less than 15% [15], [16] to up to 100% of tumors [18], [24]. Similarly, results for SSTR1 have varied, and when assessed, SSTR5 has been shown to be positive in less than 50% of tumors in most studies [14], [15], [16], [18]. Differences in SSTR subtypes between tumors from patients with familial tumor syndromes and those with sporadic tumors have only been assessed in one study with only small numbers of hereditary tumors, and differences in SSTR expression were not identified [18]. A further study identified SSTR2a staining in 2 patients with a germline SDHD mutation, but there was no control group [25]. Studies assessing SSTR expression have used a variety of methods including reverse transcriptase polymerase chain reaction and immunohistochemistry (IHC). In addition to varying methods used, until recently interpretation has further been hampered by the lack of specific monoclonal antibodies against the 5 SSTR subtypes. Fischer et al [27] briefly reported the use of the monoclonal antibody UMB-1 against SSTR2A in a number of normal and neoplastic tissues including PCs, in which most tumors demonstrated positive staining. Use of monoclonal antibodies against the other SSTRs has not been reported in PC/PGLs. Recently, a novel somatostatin analogue has been developed, pasireotide, which has activity at a wider range of SSTRs than octreotide (all SSTRs with the exception of SSTR4) [28]. The role of pasireotide in patients with metastatic and/or inoperable PC/PGL is not known, but cell culture studies have suggested that it is more promising than octreotide [21]. Based on the results of SSTR status, evidence of expression of SSTRs other than SSTR4 would support a targeted trial of this agent (unlabeled and/or labeled to radionuclides) in patients with metastatic/inoperable PC/PGL.

The aims of this study were (1) to assess the somatostatin receptor status of PC/PGLs using specific monoclonal antibodies against somatostatin receptor subtypes 1 to 5 and (2) to determine whether somatostatin receptor subtype expression varies in SDH-deficient tumors when compared with tumors showing a normal pattern of SDHB staining.

Section snippets

Materials and methods

Patients who had undergone previous surgery for PC or PGL were identified from the Waikato Hospital endocrine unit, Hamilton, New Zealand, and the Royal North Shore Hospital anatomical pathology department, Sydney, Australia. Ethical approval was obtained from the Northern Y Regional Ethics Committee (NTY/11/05/049) and in accordance with the Human Tissue Act for the New Zealand and Australian samples, respectively. Results of germline genetic testing for PC/PGL predisposition genes (SDHA, SDHB

Results

A total of 182 PC/PGL specimens were identified from 174 patients. Of the 182 tumors, 129 were adrenal, 44 extra-adrenal (of which 18 were head and neck), and 9 metastases (all from PC).

Discussion

SSTR immunostaining of PC or PGLs varies according to receptor subtype. Most tumors demonstrated positive staining for SSTR1, whereas most tumors did not stain for SSTR4 or SSTR5, irrespective of whether tumors were SDH deficient or not. SSTR2a and SSTR3 expression patterns were more variable.

Both SSTR2A and SSTR3 staining was significantly different between SDH deficient and those with normal SDH staining patterns. We have found SDHB IHC to be a robust and reliable marker of SDH mutation [30],

Conclusion

SDH-deficient tumors are more likely to demonstrate positive SSTR2a and SSTR3 immunostaining than tumors with a normal SDH staining pattern. These findings suggest that the role of somatostatin analogue therapy (unlabeled or radiolabeled) should be reexamined in the context of the underlying SDH status. Somatostatin analogue therapy may have a particular therapeutic role in patients with an underlying SDH germline mutation and for HNPGLs in patients without an underlying SDH mutation.

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    Funding/Support: The authors acknowledge Novartis Pharmaceuticals Ltd for donating monoclonal antibodies against SSTR1, SSTR3, and SSTR4. This work was supported by a Waikato Medical Research Foundation project grant (WMRF Grant Nos. 188, 2011) to M.S.E. and by the Cancer Institute NSW through the translational cancer research center program.

    ☆☆

    Competing interest: The authors declare no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

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