Presence of IGF-I in human midgut carcinoid tumours--an autocrine regulator of carcinoid tumour growth?

Targeted Therapies in the Management of Well-Differentiated Digestive and Lung Neuroendocrine Neoplasms

OPINION STATEMENT

Ongoing advances in our understanding of neuroendocrine tumor (NET) biology, genetics, and immunology, will continue to expand the availability of targeted therapies, thus improving the outcomes of patients. Well-differentiated neuroendocrine tumors (NETs) are grouped into pancreatic and non-pancreatic NETs (includes GI and thoracic NETs) for treatment considerations (Fig. 1). For panNETs, initial therapy is driven by the need of radiographic response, and targeted agents are typically reserved for second and third line based on the toxicity profile. Treatment options for non-pancreatic NETs are also expanding and while SSAs are the typical first-line option, everolimus and PRRT both remain approved therapies for future lines, and VEGF TKIs are showing promising results in research settings. Sequencing these agents and best time to incorporate peptide receptor radio therapy into the management algorithm remains an unmet need.

Can insulin-like growth factor 1 (IGF-1), IGF-1 receptor connective tissue growth factor and Ki-67 labelling index have a prognostic role in pulmonary carcinoids?

Introduction

Altered expression of Insulin-like Growth Factor-1 (IGF-1), its receptor (IGF-1R), Connective Tissue Growth Factor (CTGF) and Hypoxia Inducible Factor-1 (HIF-1), has been implicated in tumorigenesis. So far, these factors have not been studied systematically in Pulmonary Carcinoids (PCs).

Aims

To examine IGF-1, IGF-1R, CTGF and HIF-1 expression in PCs, and assess their prognostic value over established factors.

Materials & Methods

Retrospective study of 121 PCs (104 Typical and 17 Atypical). The expression of growth factors was studied immunohistochemically and tumors were considered positive if immunoreactivity appeared in >50% of cells.

Results

All studied parameters were expressed in the majority of tumors (IGF-1, IGF-1R, CTGF and HIF-1, in 78.5%, 67%, 72% and 78%, respectively). Their expression tended to be more frequent in TCs and in tumors with Ki-67≤2% (significant only for HIF-1; 82 vs. 53%; p=0.023 and 83 vs. 63%; p=0.025 respectively). CTGF was the only factor correlated with more extensive disease (larger size; presence of lymph node and distant metastases). According to logistic regression analysis, only advanced age, Ki-67≥3.4% and lymph node involvement could predict the development of distant metastases.

Conclusions

IGF-1, IGF-1R, CTGF and HIF-1 are avidly expressed in PCs; however, their presence did not appear to be of statistically significant value over established prognostic factors.

IGF-IEc expression is increased in secondary compared to primary foci in neuroendocrine neoplasms

Different Insulin-like growth factor-I (IGF-I) mRNA transcripts are produced by alternative splicing and particularly the IGF-IEc isoform has been implicated in the development and/or progression of various types of cancer. In the present study, we examined the potential role of IGF-IEc expression as a new immunohistochemical marker of aggressiveness in neuroendocrine neoplasms (NENs). We utilized immunohistochemical analysis in tissue specimens of 47 patients with NENs, to evaluate the expression of IGF-IEc (%) and Ki-67 proliferation index (%). Specimens from patients with tumors of different tissue origin, of either primary or metastatic lesions and of different grade were examined. Cytoplasmic IGF-IEc staining was found in 23 specimens of NENs or NECs: 10 pancreatic, 4 small bowel, 3 gastric, 1 lung, 1 uterine and 4 poorly differentiated of unknown primary origin. Ki-67 and IGF-IEc expression was positively correlated in all the samples studied (r=0.31, p=0.03). IGF-1Ec expression was more prevalent in specimens originating from metastatic foci with high Ki-67 compared to primary sites with low Ki-67 expression (p=0.036). These findings suggest a possible role of IGF-IEc in NEN tumorigenesis and progression to metastases that could be used as an additional new marker of a more aggressive behavior and a potential drugable target.

Successful treatment of refractory midgut bleeding with ocreotide and corticosteroids in a dialysis patient with suspected sarcoidosis

We present a case of severe and recurrent small-bowel bleeding, due to multiple intestinal angiodysplasias, in a female patient with chronic renal failure due to suspected sarcoidosis. Over the years, she required numerous admissions and >200 units of blood for symptomatic anaemia. However, following a small-bowel capsule endoscopy that revealed several small-bowel angiectasis, she was treated successfully with octreotide and corticosteroids. Her transfusion requirements and hospital admissions were reduced drastically. Moreover, hypercalcaemia and liver function tests also normalised after treatment and double-balloon enteroscopy confirmed the complete resolution of these angiodysplasias. This case presentation confirms the usefulness of octreotide in the management of small-bowel angiodysplasias in dialysis patients and highlights the additional benefit of corticosteroids in portal hypertension due to suspected sarcoidosis.

Towards a new classification of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) constitute a heterogeneous group of tumours associated with variable clinical presentations, growth rates, and prognoses. To improve the management of GEP-NENs, the WHO developed a classification system that enables tumours to be graded based on markers of cell proliferation in biopsy specimens. Indeed, histopathology has been a mainstay in the diagnosis of GEP-NENs, and the WHO grading system facilitates therapeutic decision-making; however, considerable intratumoural heterogeneity, predominantly comprising regional variations in proliferation rates, complicates the evaluation of tumour biology. The use of molecular imaging modalities to delineate the most-aggressive cell populations is becoming more widespread. In addition, molecular profiling is increasingly undertaken in the clinical setting, and genomic studies have revealed a number of chromosomal alterations in GEP-NENs, although the 'drivers' of neoplastic development have not been identified. Thus, our molecular understanding of GEP-NENs remains insufficient to inform on patient prognosis or selection for treatments, and the WHO classification continues to form the basis for management of this disease. Nevertheless, our increasing understanding of the molecular genetics and biology of GEP-NENs has begun to expose flaws in the WHO classification. We describe the current understanding of the molecular characteristics of GEP-NENs, and discuss how advances in molecular profiling measurements, including assays of circulating mRNAs, are likely to influence the management of these tumours.

The prevalence and relevance of adrenal masses in patients with sporadic gastroenteropancreatic neuroendocrine tumours (GEP-NET)

OBJECTIVE

The widespread application of abdominal computerized tomography (CT) imaging has revealed that 0.98-4.0% of individuals harbour adrenal lesions (incidentalomas). There is, however, paucity of information regarding the prevalence of adrenal lesions in patients with gastroenteropancreatic neuroendocrine tumours (GEP-NETS). Purpose of this study was to estimate the prevalence of adrenal lesions in patients with GEP-NETS and identify their radiological features and clinical significance.

DESIGN

The prevalence of adrenal lesions was estimated retrospectively in 438 patients with GEP-NETS who underwent abdominal imaging. Secretory status and changes in size were documented during subsequent follow-up. MEN-1 patients and ectopic ACTH-secreting tumours were excluded.

RESULTS

Adrenal lesions were detected in 32 (8.4%) of 383 patients included. The majority (22 patients - 69%) were located at the left adrenal gland and the mean size was 23.6 mm. In two patients, one with a well and another with a poorly differentiated tumour, clinicopathological features suggested adrenal metastases. During a mean follow-up period of 69.5 months, no subsequent growth of any adrenal lesion was observed. Endocrine evaluation documented subclinical glucocorticoid hypersecretion in 4 cases (14%). The presence of adrenal lesions did not correlate to distant metastases, however, they were observed more frequently in patients with G3 tumours.

CONCLUSION

The prevalence of adrenal lesions in patients with GEP-NETs was found to be higher than the general population and mostly represent benign adrenal adenomas (except patients with G3 tumours). Nevertheless, individualized assessment of imaging characteristics should be still considered.

Serotonin and the 5-HT7 receptor: the link between hepatocytes, IGF-1 and small intestinal neuroendocrine tumors

Platelet-derived serotonin (5-HT) is involved in liver regeneration. The liver is also the metastatic site for malignant enterochromaffin (EC) cell "carcinoid" (neuroendocrine) neoplasms, the principal cellular source of 5-HT. We hypothesized that 5-HT produced by metastatic EC cells played a role in the hepatic tumor-microenvironment principally via 5-HT₇ receptor-mediated activation of hepatocyte IGF-1 synthesis and secretion. Using isolated rat hepatocytes, we evaluated 5-HT₇ receptor expression (using PCR, sequencing and western blot). ELISA, cell transfection and western blots delineated 5-HT-mediated signaling pathways (pCREB, AKT and ERK). IGF-1 synthesis/secretion was evaluated using QPCR and ELISA. IGF-1 was tested on small intestinal neuroendocrine neoplasm proliferation, while IGF-1 production and 5-HT₇ expression were examined in an in vivo SCID metastasis model. Our results demonstrated evidence for a functional 5-HT₇ receptor. 5-HT activated cAMP/PKA activity, pCREB (130-205%, P < 0.05) and pERK/pAKT (1.2-1.75, P < 0.05). Signaling was reversed by the 5-HT₇ receptor antagonist SB269970. IGF-1 significantly stimulated proliferation of two small intestinal neuroendocrine neoplasm cell lines (EC₅₀: 7-70 pg/mL) and could be reversed by the small molecule inhibitor BMS-754807. IGF-1 and 5-HT were elevated (40-300×) in peri-tumoral hepatic tissue in nude mice, while 5-HT₇ was increased fourfold compared to sham-operated animals. We conclude that hepatocytes express a cAMP-coupled 5-HT₇ receptor, which, at elevated 5-HT concentrations that occur in liver metastases, signals via CREB/AKT and is linked to IGF-1 synthesis and secretion. Because IGF-1 regulates NEN proliferation, identification of a role for 5-HT₇ in the hepatic metastatic tumor microenvironment suggests the potential for novel therapeutic strategies for amine-producing mid-gut tumors.

Signaling pathways as specific pharmacologic targets for neuroendocrine tumor therapy: RET, PI3K, MEK, growth factors, and Notch

Neuroendocrine tumors are rare tumors with a common progenitor - the neural crest cell. Included in this category are pulmonary and gastrointestinal tract carcinoid tumors and medullary thyroid cancer. The majority of these tumors are sporadic in nature, however they can be hereditary. Medullary thyroid cancers can present sporadically, with other endocrine tumors, as in the complex of multiple endocrine neoplasias 1, 2A, or 2B, or as familial medullary thyroid cancer. These tumors can become evident at later stages, with metastases already present at the time of diagnosis. Despite the small size and rare incidence of gastrointestinal neuroendocrine (carcinoid) tumors, they can be debilitating when present. Their natural history presents as early lymph node and distant metastases, as well as symptoms of the carcinoid syndrome, which result from the overproduction and secretion of serotonin and somatostatin. As a consequence of their metastases, surgical resection is non-curative and hence there is a need for novel treatment strategies to address tumor burden and symptom control. There are multiple intracellular pathways which can be targeted, either individually or in combination, to address these tumors. Here, we review some of the intracellular pathways, and identify some specific targets, which are vital to the generation and propagation of neuroendocrine tumorigenesis, and thus, can be the foci of novel drug therapies. We also elaborate on present pharmacological strategies and clinical trials involving these intracellular pathways.

Profiling of ileal carcinoids

Identification of common molecular mechanisms is needed to facilitate the development of new treatment options for patients with ileal carcinoids.

PURPOSE OF REVIEW

Recent profiling studies on ileal carcinoids were examined to obtain a comprehensive view of risk factors, genetic aberrations, and transcriptional alterations. Special attention was paid to mechanisms that could provide novel targets for therapy.

RESULTS

Genome-wide association studies have shown that single nucleotide polymorphisms (SNPs) at IL12A and DAD1 are associated with an increased risk of ileal carcinoids. Genomic profiling revealed distinct patterns of copy-number alterations in ileal carcinoids. Two groups of carcinoids could be identified by hierarchical clustering. A major group of tumors was characterized by loss on chromosome 18 followed by additional losses on chromosomes 3p, 11q, and 13. Three minimal common regions of deletions were identified at 18q21.1-q21.31, 18q22.1-q22.2, and 18q22.3-q23. A minor group of tumors was characterized by clustered gains on chromosomes 4, 5, 7, 14, and 20. Expression profiling identified three groups of ileal carcinoids by principal component analysis. Tumor progression was associated with changes in gene expression including downregulation of MIR133A. Candidate genes for targeted therapy included ERBB2/HER2, DAD1, PRKCA, RYBP, CASP1, CASP4, CASP5, VMAT1, RET, APLP1, OR51E1, GPR112, SPOCK1, RUNX1, and MIR133A.

CONCLUSION

Profiling of ileal carcinoids has revealed recurrent genetic alterations and distinct patterns of gene expression. Frequent alterations in cellular pathways and genes were identified, suggesting novel targets for therapy. Translational studies are needed to validate suggested molecular targets.

Connective tissue growth factor in tumor pathogenesis

Key roles for connective tissue growth factor (CTGF/CCN2) are demonstrated in the wound repair process where it promotes myofibroblast differentiation and angiogenesis. Similar mechanisms are active in tumor-reactive stroma where CTGF is expressed. Other potential roles include prevention of hypoxia-induced apoptosis and promoting epithelial-mesenchymal transistion (EMT). CTGF expression in tumors has been associated to both tumor suppression and progression. For example, CTGF expression in acute lymphoblastic leukemia, breast, pancreas and gastric cancer correlates to worse prognosis whereas the opposite is true for colorectal, lung and ovarian cancer. This discrepancy is not yet understood. High expression of CTGF is a hallmark of ileal carcinoids, which are well-differentiated endocrine carcinomas with serotonin production originating from the small intestine and proximal colon. These tumors maintain a high grade of differentiation and low proliferation. Despite this, they are malignant and most patients have metastatic disease at diagnosis. These tumors demonstrate several phenotypes potentially related to CTGF function namely: cell migration, absent tumor cell apoptosis, as well as, reactive and well vascularised myofibroblast rich stroma and fibrosis development locally and in distal organs. The presence of CTGF in other endocrine tumors indicates a role in the progression of well-differentiated tumors.

Potential synergies for combined targeted therapy in the treatment of neuroendocrine cancer

Well differentiated neuroendocrine tumours (WDNET) are a diverse group of cancers that are often advanced at the time of diagnosis and generally do not respond significantly to traditional chemotherapy. A number of intriguing therapeutic targets have emerged, including somatostatin receptors, insulin-like growth factor-1 (IGF-1) and its receptor (IGF-1R), the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway, and vascular endothelial growth factor receptor. Functional somatostatin receptors and IGF-1R as well as dysregulated mTOR--a key pathway component for both growth factor signalling and protein synthesis--have been identified in human neuroendocrine tumour (NET) cell lines. Somatostatin analogues (SSA) and mTOR inhibitors have exhibited in vitro and in vivo antitumour activity against NET and have shown effects on the IGF-1 pathway in preclinical studies. SSA inhibit PI3K/Akt signalling upstream of mTOR, suggesting that the combination of an SSA and an mTOR inhibitor may have greater efficacy than either as single agents. Recent clinical trial experience has provided some encouraging findings and prompted the design of additional studies of this dual-targeted approach to treating advanced WDNET. Results of ongoing trials of dual-targeted therapy combinations will define future therapies for advanced WDNET.

Limitations in small intestinal neuroendocrine tumor therapy by mTor kinase inhibition reflect growth factor-mediated PI3K feedback loop activation via ERK1/2 and AKT

BACKGROUND

Treatment of small intestinal neuroendocrine tumors (SINETs) with mammalian target of rapamycin (mTOR) inhibitors alone or with somatostatin analogs has been proposed as effective therapy, because both agents have been reported to exhibit antiproliferative activity. Because adenocarcinomas escape mTOR inhibition, we examined whether the escape phenomenon occurred in SINETs and whether usage of somatostatin analogs with mTOR inhibitors surmounted loss of inhibition.

METHODS

The effects of the somatostatin analog octreotide (OCT), the mTOR inhibitor RAD001 (RAD), or the combination were evaluated in SINET cell lines (KRJ-I, H-STS) using cell viability assays, western blotting, enzyme-linked immunosorbent assay, and reverse-transcription polymerase chain reaction to assess antiproliferative signaling pathways and feedback regulation.

RESULTS

RAD (10(-9) M) incompletely decreased cell viability (-40% to +15%); growth escape (P < .001) was noted at 72 hours in both cell lines. Phosphorylated (p)mTOR/mTOR and pp70S6K/p70S6K ratios were decreased but were associated with increases in phosphorylated extracellular signal-regulated kinase (pERK)/ERK and pAKT/AKT in both cell lines, whereas phosphorylated insulin-like growth factor 1 receptor (pIGF-1R)/IGF-1R levels were elevated only in H-STS cells. Increased (P < .05) transcript levels for AKT1, MAPK, mTOR, IGF-1R, IGF-1, and TGFβ1 were evident. OCT (10(-6) M) itself had no significant effect on growth signaling in either cell line. An antiproliferative effect (66 ± 5%) using OCT+RAD was only noted in the KRJ-I cells (P < .05).

CONCLUSIONS

SINET treatment with the mTOR inhibitor RAD had no antiproliferative effect based on activation of pAKT and pERK1/2. A combinatorial approach using OCT and RAD failed to overcome this escape phenomenon. However, differences in RAD response rates in individual NET cell lines suggested that pretreatment identification of different tumor sensitivity to mTOR inhibitors could provide the basis for individualized treatment.

Biological targeted therapies in patients with advanced enteropancreatic neuroendocrine carcinomas

Enteropancreatic (EP) neuroendocrine carcinomas (NECs) represent relatively rare and heterogeneous malignancies. They are the most common group among neuroendocrine tumors (NETs). In most cases they are advanced at diagnosis and slow-growing, therefore conditioning a better prognosis compared with non neuroendocrine carcinomas from the same sites. No standard medical therapy exists, except for somatostatin analogs in functioning tumors, and octreotide LAR in functioning or non functioning well differentiated NECs from small bowel. Several systemic therapeutic options exist, including chemotherapy, somatostatin analog, interferon, peptide receptor radionuclide therapy (PRRT), and molecular targeted drugs. Among them some therapies have specific biological tumor targets and can be defined as "biological targeted therapies". This review focuses on the status of EP NECs targeted therapies in the light of recent advances. Somatostatin receptors (SSTRs) are the first therapeutic target detected in EP NECs. Through them SS analogs and PRRT act, producing symptomatic, biochemical, and, to a lesser extent, antiproliferative effects. New SS analogs, covering a higher number of SSTR subtypes, were developed, including pasireotide (SOM230), which controls 25% of carcinoid syndromes resistant to full dose octreotide LAR. Chimeric analogs, which bind SSTR2/SSTR5 and dopamine-2 receptor subtype (D2), are in preclinical phase of development. Among the numerous molecular targeted agents investigated in NETs, mTOR inhibitors and VEGF/VEGFR/PDGFR inhibitors are in most advanced clinical phase of investigation. In particular, everolimus, sunitinib, and bevacizumab are all studied in phase III trials. Both everolimus and sunitinib produced significant survival benefit versus placebo in advanced progressing well-differentiated pancreatic NECs. Sunitinib data have been presented at the last ASCO in June 2010, and everolimus data will be presented at next ESMO in September 2010.

An analysis of trends and growth factor receptor expression of GI carcinoid tumors

INTRODUCTION

The purpose of our study was twofold: (1) to determine the incidence, patient and tumor characteristics, and outcome of patients with gastrointestinal carcinoid tumors using the Surveillance, Epidemiology and End Results (SEER) database, and (2) to delineate the expression pattern of growth factor receptors (GFRs) in carcinoid tumors.

MATERIALS AND METHODS

The SEER database search provided information on patients diagnosed with carcinoid tumors from 1990 to 2002. Carcinoid tumor sections (n = 46) were stained for the GFRs: epidermal growth factor receptor, insulin-like growth factor receptor (IGFR), vascular endothelial growth factor receptor (VEGFR), and HER-2/neu.

RESULTS

Over the 12-year analysis period, 18,180 patients were identified with carcinoid tumors of the foregut, midgut, and hindgut; the incidence of carcinoid tumors increased approximately 2-fold during this time period. Of the patients with carcinoid tumors, there was a trend of increased expression of VEGFR and IGFR, particularly in the foregut and midgut carcinoids. Analysis of the SEER database confirms that the incidence of carcinoid tumors is increasing with an approximate doubling in the number of carcinoid cases from 1990 to 2002. Furthermore, an increase in VEGFR and IGFR expression suggests that GFR inhibitors may be effective adjuvant therapy for carcinoid cancer.

Effects of type I interferons on IGF-mediated autocrine/paracrine growth of human neuroendocrine tumor cells

We recently demonstrated that interferon (IFN)-beta has a more potent antitumor activity than IFN-alpha in BON cells, a neuroendocrine tumor (NET) cell line. The present study showed the role of type I IFNs in the modulation of the insulin-like growth factor (IGF) system in NETs. BON cells expressed IGF-I, IGF-II, IGF-I receptor, and insulin receptor mRNA. In addition, IGF-I and IGF-II stimulated the proliferation of BON cells and induced an inhibition of DNA fragmentation (apoptosis). As evaluated by quantitative RT-PCR, treatment with IFN-alpha (100 IU/ml) or IFN-beta (100 IU/ml) inhibited the expression of IGF-II mRNA (-42% and -65%, respectively, both P < 0.001), whereas IGF-I receptor mRNA was significantly upregulated by IFN-alpha (+28%, P < 0.001) and downregulated by IFN-beta (-47%, P < 0.001). Immunoreactive IGF-II concentration decreased in the conditioned medium during IFN-alpha (-16%, P < 0.05) and IFN-beta (-69%, P < 0.001) treatment. Additionally, IGF-I receptor bioactivity was reduced (-54%) after IFN-beta treatment. Scatchard analysis of (125)I-labeled IGF-I binding to cell membrane of BON cells revealed a dramatic suppression of maximum binding capacity only in the presence of IFN-beta. Finally, the proapoptotic activity of IFN-beta was partially counteracted by the coadministration of IGF-I and IGF-II (both at 50 nM). In conclusion, these data demonstrate that the IGF system has an important role in autocrine/paracrine growth of BON cells. The more potent antitumor activity of IFN-beta compared with IFN-alpha could be explained by several effects on this system: 1) both IFNs inhibit the transcription of IGF-II, but the suppression is significantly higher after IFN-beta than IFN-alpha and 2) only IFN-beta inhibits the expression of IGF-I receptor.

Treatment of advanced disease in patients with well-differentiated neuroendocrine tumors

Well-differentiated neuroendocrine tumors (NETs), which are also referred to as well-differentiated endocrine carcinoma according to WHO terminology, are usually slow-growing cancers, even when they exhibit gross local invasion and/or metastases. The survival of patients with metastatic NET is often measured in years to decades. Once NET progresses or becomes symptomatic the patient's prognosis is poor. An important challenge for clinicians is to distinguish at an early stage those patients who will die with the disease, from those who will succumb because of it, so that the appropriate level of care can be administered. Reliable genomic predictors could provide substantial advancements in prognosis and, possibly, treatment; however, such markers are currently unavailable. Early literature on the treatment of NETs is confounded by a lack of formal objective response criteria. Somatostatin analogs can control symptoms and can stabilize some slow-growing tumors, but rarely result in tumor regression. Surgery is curative in only a minority of patients, and systemic chemotherapy is minimally effective. Advances in the understanding of tumor biology have led to the identification of important cellular processes involved in the pathogenesis of NETs, and agents that target these processes have now entered clinical trials. We will discuss the data on therapies currently used to treat well-differentiated NETs, and the strategies being used in clinical trials.

Treatment of gastrointestinal neuroendocrine tumors with inhibitors of growth factor receptors and their signaling pathways: recent advances and future perspectives

The limited efficacy of conventional cytotoxic treatment regimes for advanced gastrointestinal neuroendocrine cancers emphasizes the need for novel and more effective medical treatment options. Recent findings on the specific biological features of this family of neoplasms has led to the development of new targeted therapies, which take into account the high vascularization and abundant expression of specific growth factors and cognate tyrosine kinase receptors. This review will briefly summarize the status and future perspectives of antiangiogenic, mTOR- or growth factor receptor-based pharmacological approaches for the innovative treatment of gastrointestinal neuroendocrine tumors. In view of the multitude of novel targeted approaches, the rationale for innovative combination therapies, i.e. combining growth factor (receptor)-targeting agents with chemo- or biotherapeutics or with other novel anticancer drugs such as HDAC or proteasome inhibitors will be taken into account.

Neuroendocrine tumors. Molecular targeted therapy for carcinoid and islet-cell carcinoma

Carcinoid and islet-cell carcinoma are often also known as low-grade neuroendocrine carcinomas. They are often slow-growing but can be resistant to standard therapy. While somatostatin analogues are often used to control hormonal syndromes, there is currently no therapy approved in the US for control of carcinoid tumor growth. For islet-cell carcinoma, streptozocin-based chemotherapy may induce tumor shrinkage, but second-line option are limited. This chapter reviews the molecular biology of neuroendocrine tumors, including the roles of MENIN, TSC2, NF-1, vHL, p53, bcl-2, bax, VEGF, IGF, PDGF, EGFR, and mTOR. Recently, there has been interest in developing molecularly targeted therapy for this group of diseases. Phase-II studies with imatinib, bevacizumab, sunitinib, gefitnib, temsirolimus, and everolimus (RAD001) have completed accrual. Encouraging results have been observed in studies with VEGF and mTOR inhibitors. Phase-III study of bevacizumab is planned in the US. Large-scale multinational phase-II and -III studies of everolimus are under way.

Long-term efficacy of octreotide in the prevention of recurrent bleeding from gastrointestinal angiodysplasia

OBJECTIVES

Preliminary studies suggested that octreotide may be therapeutic in bleeding angiodysplasia. Our aim was to investigate the efficacy of long-term octreotide therapy in the prevention of rebleeding from gastrointestinal angiodysplasia.

METHODS

A cohort of 32 patients diagnosed with bleeding from angiodysplasia was treated with octreotide 50 mu 12 h subcutaneously for a 1-2 yr period. This cohort was compared with an external control group (38 patients who had received placebo [1 tablet/day] in a concurrent randomized clinical trial for the same period.

RESULTS

Two patients of the octreotide group were lost to follow-up. Treatment failure occurred in seven of 30 (23%) patients in the octreotide group and in 17 of 35 (48%) in the placebo group (three dropouts before first visit) (P= 0.043). The actuarial probability of remaining free of rebleeding at 1 and 2 yr of follow-up was 77% and 68%, respectively, for the octreotide group and 55% and 36%, respectively, for the placebo group (log rank P= 0.030). Multivariate proportional hazards-regression analysis showed that octreotide therapy and previous bleeding episodes were positive and negative predictors of efficacy, respectively. No significant differences between the groups were observed according to number of bleeding episodes (0.4 +/- 0.7 vs 0.9 +/- 1.5, P= 0.070) and transfusion requirements (1.1 +/- 2.6 vs 0.7 +/- 1.5 units); however, iron requirements were lower in the octreotide than in the placebo group (22 +/- 62 vs 166 +/- 267 units; P < 0.001). Likewise, major adverse events (1 vs 1) and mortality (0 vs 1) were similar between groups.

CONCLUSIONS

This study suggests that octreotide treatment may be beneficial in preventing rebleeding from gastrointestinal angiodysplasia.

Increased expression of insulin-like growth factor I and/or its receptor in gastrinomas is associated with low curability, increased growth, and development of metastases

PURPOSE

Growth factors, particularly insulin-like growth factor I (IGF-I) and IGF-I receptor (IGF-IR) in some nonendocrine and a few endocrine tumors, are thought important in recurrence, growth, and aggressiveness. Whether this is true of neuroendocrine tumors such as gastrinomas is unclear. The aim of this study was to address this question in gastrinomas.

EXPERIMENTAL DESIGN

IGF-I and IGF-IR expression in gastrinomas from 54 patients with Zollinger-Ellison syndrome were analyzed and correlated with clinical/tumor characteristics. IGF-I and IGF-IR mRNA levels were determined by competitive reverse transcription-PCR. IGF-IR expression, assessed by immunohistochemistry, was done on a subset.

RESULTS

IGF-IR mRNA was found in 100% and IGF-I in 89%. IGF-I mRNA expression varied by >254-fold, IGF-IR by 2,670-fold, and the levels correlated in a given tumor. The IGF-IR level was lower in gastrinomas of patients who were rendered disease free and increased levels correlated with tumor growth, aggressiveness, extent, and with liver metastases. Increased IGF-I levels correlated with increased growth, tumor extent, and aggressiveness. Neither IGF-IR nor IGF-I levels correlated with tumor location, size, or its clinical/functional features. The IGF-IR correlated with disease-free survival. IGF-IRbeta was found in 31 of 32 tumors (97%) by immunohistochemistry.

CONCLUSIONS

These results indicate that IGF-I and IGF-IR are expressed in almost all gastrinomas. Furthermore, assessment of IGF-I/IGF-IR expression in gastrinomas may be clinically useful in identifying those patients with more aggressive tumors who might benefit from more aggressive treatment.

Insulin-like growth factor 1 signaling in human gastrointestinal carcinoid tumor cells

Background Insulin-like growth factor 1 (IGF-1) is an autocrine regulator of carcinoid tumors. Blockade of IGF-1 signaling has been proposed as a therapeutic target in the treatment of patients with carcinoid syndrome. We hypothesized that the induction of parallel raf-1/MEK1 pathways will block IGF-1-mediated chromogranin A (CgA) maintenance. Methods Human gastrointestinal carcinoid tumor cells (BON) were treated with IGF-1 (0-500 ng/mL). Raf-1/MEK1 activation was achieved with an estrogen-inducible raf-1 vector that was transduced into BON cells. Activation of IGF-1/raf-1 pathways was determined by phosphorylation of downstream targets p70s6 and ERK1/2. The secreted and intercellular levels of CgA were measured in conditioned media and whole cell extracts by Western and enzyme-linked immunosorbent assay analysis. Results IGF-1 and raf-1 pathways were activated successfully in BON cells, as shown by high levels of phosphorylated p70s6 and phosphorylated ERK1/2, respectively. Treatment of BON cells with IGF-1 stimulated the release of CgA, while high intracellular CgA levels were maintained. The activation of raf-1/MEK1 reversed the effect of IGF-1 treatment by the depletion of intracellular CgA. Conclusions The induction of the raf-1/MEK1 pathway blocks IGF-1-mediated intracellular neuroendocrine hormone regulation. Therefore, raf-1/MEK1 activation may be a viable method to block IGF-1-mediated cellular effects and serve as a therapeutic target in gastrointestinal carcinoid tumors.

Independent value of fascin immunoreactivity for predicting lymph node metastases in typical and atypical pulmonary carcinoids

Immunoreactivity for fascin, an actin-bundling protein related to cell motility, has been reported in breast, ovary, pancreas, skin, and non-small cell carcinomas, and associated with more advanced disease stage and poorer prognosis. Data on pulmonary neuroendocrine (NE) tumors, however, are lacking. We evaluated the expression of fascin by immunohistochemistry--using two different monoclonal antibodies--in surgical specimens of pulmonary NE tumors of all the diverse histological types from 128 consecutive patients recruited between 1987 and 2001, and investigated its relationship with the presence of lymph node metastases. Overall, fascin immunoreactivity was detected in 5% of 38 typical carcinoids (TC), 35% of 23 atypical carcinoids (AC), 83% of 40 large-cell neuroendocrine carcinomas (LCNEC), and 100% of 27 small-cell lung carcinomas (SCLC) (P<0.001), Normal NE cells or hyperplastic NE tumorlets were consistently unreactive. No statistically significant differences in fascin immunoreactivity were found between the two antibodies. In TC and AC but not high-grade NE tumors, fascin immunoreactivity closely correlated with the occurrence of lymph node metastases, the pN class and the number of involved lymph nodes (P<0.001). It was also significantly associated with an increased proliferative activity (Ki-67 labeling index >5%) (P=0.020), and with either down-regulation or altered subcellular compartmentalization of E-cadherin (P<0.001) and CD99 (P=0.030), two cell adhesion complexes in pulmonary NE tumors. At multivariate analysis, only fascin emerged as an independent predictor of lymph node metastases in this tumor group (HR 30.28; 95% confidence intervals: 1.59-574.49; P=0.023). This study indicates that fascin immunoreactivity may identify subsets of pulmonary carcinoid patients with different metastatic potential to regional lymph nodes. Targeting the fascin pathway could be a novel therapeutic strategy of pulmonary carcinoids.

Molecular insights into gastrointestinal neuroendocrine tumours: importance and recent advances

A subset of gastrointestinal neuroendocrine tumours (carcinoids and pancreatic endocrine tumours) show aggressive growth. Early identification of this subset is essential for management; however, clinical, laboratory and histologic features frequently fail to achieve this. Currently, there is an increased understanding of the molecular pathogenesis/changes in neuroendocrine tumours and this may identify important prognostic factors and possibly, new treatments. Recent findings and progress in this area are briefly reviewed in this article.

Immunohistochemical detection of fibroblast growth factor receptors in normal endocrine cells and related tumors of the digestive system

Endocrine tumors (ETs) of the digestive system produce several growth factors including acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), which are thought to be involved in the growth of tumor cells and in the proliferation of tumor stromal cells. Their actions depend on binding to four specific receptors--FGFR1, FGFR2, FGFR3, and FGFR4--whose distribution in normal endocrine cells and related tumors of the gastroenteropancreatic (GEP) system has previously been examined. Formalin-fixed, paraffin-embedded normal tissues and 60 well-characterized GEP endocrine tumors were immunostained using specific antibodies directed against various GEP hormones, aFGF, FGFR1, FGFR2, FGFR3, and FGFR4. Acidic FGF immunoreactivity (IR) was found in gut EC cells; FGFR1 immunoreactivity in rare duodenal endocrine cells and in pancreatic A cells; FGFR2 immunoreactivity in gastric and duodenal G cells, pancreatic B cells, and rectal EC cells; FGFR3 immunoreactivity in duodenal G cells; and FGFR4 immunoreactivity in rectal L cells and in pancreatic B, PP, and A cells. Immunoreactivity for at least one of the four FGFRs was found in all tumors, independently of FGFR expression in the putative cell of origin. EC cell tumors, which were all positive for aFGF, were found to express at least three different FGFRs. FGFRs also were localized in the stromal cells of all the tumors examined. The tumor stroma was more abundant in EC cell tumors than in other types of neoplasms. The results suggest that aFGF-FGFR interaction may be involved in the modulation of normal endocrine cell functions and in the regulation of tumor growth and stromal proliferation of EC cell carcinoids.

A transplantable human carcinoid as model for somatostatin receptor-mediated and amine transporter-mediated radionuclide uptake

A human midgut carcinoid tumor was successfully transplanted into nude mice and propagated for five consecutive generations (30 months) with well-preserved phenotype. Tumor cells in nude mice expressed identical neuroendocrine markers as the original tumor, including somatostatin receptors (somatostatin receptors 1 to 5) and vesicular monoamine transporters (VMAT1 and VMAT2). Because of the expression of somatostatin receptors and VMAT1 and VMAT2 the grafted tumors could be visualized scintigraphically using the somatostatin analogue 111In-octreotide and the catecholamine analogue 123I-metaiodobenzylguanidine. The biokinetics of the somatostatin analogue 111In-octreotide in the tumors was studied and showed a high retention 7 days after administration. Cell cultures were re-established from transplanted tumors. Immunocytochemical and ultrastructural studies confirmed the neuroendocrine differentiation. The human origin of transplanted tumor cells was confirmed by cytogenetic and fluorescence it situ hybridization analyses. Spontaneous secretion of serotonin and its metabolite, 5-hydroxyindole acetic acid, from tumor cells was demonstrated. The tumor cells increased their [Ca2+]i in response to beta-adrenoceptor stimulation (isoproterenol) and K+-depolarization. All somatostatin receptor subtypes could be demonstrated in cultured cells. This human transplantable carcinoid tumor, designated GOT1, grafted to nude mice, will give unique possibilities for studies of somatostatin receptor- and VMAT-mediated radionuclide uptake as well as for studies of secretory mechanisms.

Carcinoid-related angiomatous polyposis simulating Crohn disease

Polyposis associated with ileal carcinoid tumors is a rarely described pathologic mucosal transformation that may simulate inflammatory or neoplastic polyps. We describe a case with innumerable sessile polyps and groups of large filiform-like polyps of the terminal ileum associated with submucosal carcinoid tumors and a large mesenteric carcinoid tumor mass. The clinical, radiographic, and endoscopic presentation of the polyposis, together with the presence of multiple small bowel stenotic lesions, simulated Crohn disease. We propose the descriptive terminology angiomatous polyposis to describe the striking microscopic vascular proliferation that characterizes these polyps. The distribution of these lesions, with the most profuse polyposis in the immediate proximity of the carcinoid nests, and the immunohistochemical demonstration of growth factor substances, such as transforming growth factor alpha within neoplastic cells and adjacent polyps, suggest a tumor factor-mediated stromal proliferation.

The efficacy of octreotide therapy in chronic bleeding due to vascular abnormalities of the gastrointestinal tract

BACKGROUND

The treatment of angiodysplasia and watermelon stomach, vascular abnormalities implicated in gastrointestinal bleeding of obscure origin, is a major clinical problem.

AIM

To determine the efficacy of octreotide in patients with long-standing gastrointestinal bleeding due to acquired angiodysplasia and watermelon stomach, resistant to previous treatments and not suitable for surgery because of old age and/or concomitant disorders.

PATIENTS AND METHODS

We treated 17 patients (seven had isolated angiodysplasia, seven had multiple upper and lower gastrointestinal angiodysplasia, and three had watermelon stomach) with octreotide (0. 1 mg subcutaneous t.d.s. for 6 months). Six of the patients had liver cirrhosis, one had Glanzmann-type platelet derangement, two had cardiovascular diseases and one had chronic uraemia.

RESULTS

Octreotide treatment stopped bleeding in 10 patients. A transient improvement was observed in four, who needed subsequent cyclical retreatment to correct low haemoglobin levels. No effect was observed in three, probably due to the severity of the concomitant disorders.

CONCLUSIONS

Octreotide is a safe drug that may be useful to control the recurrent gastrointestinal bleeding due to acquired angiodysplasia and watermelon stomach, especially in patients who are not candidates for surgery due to old age and/or concomitant disorders.

Clinicopathological profile as a basis for classification of the endocrine tumours of the gastroenteropancreatic tract

Recent developments in the field of endocrine cell biology and pathology, at both morphologic and molecular levels, are briefly outlined and discussed as a basis for endocrine tumour characterization. The main clinicopathological tools available for the identification and characterization of endocrine tumours are discussed. Based on this, classifications of endocrine tumours of the pancreas and gastrointestinal tract are developed covering most clinical (hyperfunctional syndromes included), pathologic and biological patterns and with special emphasis on tumour prognosis.

Expression of vascular endothelial growth factor in digestive neuroendocrine tumours

AIMS

Angiogenesis is a complex multistep process essential for tumour growth. Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and vascular permeability-inducing agent. Recent studies have shown that VEGF expression is correlated to microvessel density and tumour progression. The aim of this study was to analyse VEGF expression in a series of gastrointestinal neuroendocrine tumours.

METHODS AND RESULTS

Surgical specimens from 28 gastrointestinal carcinoids and 20 pancreatic endocrine tumours were examined for VEGF expression by immunohistochemistry. Intense cytoplasmic staining for VEGF was observed in several cells of the islets of Langerhans and in neuroendocrine cells of normal digestive mucosa. All midgut carcinoids showed strong VEGF expression in tumoral cells. Positive VEGF immunostaining was observed in 16 of 20 neuroendocrine pancreatic tumours but it was usually much lower than in midgut carcinoids. Western blotting analysis in eight cases identified a major band at 30-32 kDa. No correlation between VEGF expression and tumour stage was found.

CONCLUSIONS

This study demonstrates that neuroendocrine cells are a major source of VEGF, particularly in midgut carcinoids. This finding suggests that the presence of VEGF may be required to maintain the differentiated state of capillary vessels in these hypervascular tumours. Such secretion, in conjunction with the other growth factors synthesized by these neuroendocrine tumours, may have an important role in tumour growth.

Comparative studies on the expression of somatostatin receptor subtypes, outcome of octreotide scintigraphy and response to octreotide treatment in patients with carcinoid tumours

We have compared the expression of somatostatin receptor (sstr) subtypes with the outcome of somatostatin receptor scintigraphy and the effect of somatostatin receptor activation in patients with disseminated carcinoid tumours. Tumour tissues from nine patients with midgut carcinoids (ileal) and three patients with foregut carcinoids (gastric, thymic) were analysed using Northern blotting. Expression of somatostatin receptors was demonstrated in all tumours (12 out of 12), with all five receptor subtypes present in 9 out of 12 tumours. Somatostatin receptor scintigraphy using [111In]DTPA-D-Phe1-octreotide visualized tumours in all patients (12 out of 12). The 111In activity concentrations in tumour tissue (T) and blood (B) were determined in three tumours 1-7 days after injection of the radionuclide. The T/B 111In activity concentration ratios ranged between 32 and 651. Clinically, treatment with the long-acting somatostatin analogue octreotide resulted in marked symptom relief accompanied by a significant reduction in tumour markers, for example urinary-5-HIAA levels (28-71% reduction). Incubation of midgut carcinoid tumours in primary culture with octreotide (10 microM) resulted in a reduction in spontaneously secreted serotonin (45-71% reduction) and 5-HIAA (41-94% reduction). The results demonstrate that carcinoid tumours possess multiple somatostatin receptor subtypes and that somatostatin analogues such as octreotide, which preferentially bind to somatostatin receptor subtype 2 and 5, can be used in the diagnosis and medical treatment of these tumours. In the future, novel somatostatin analogues with subtype specific receptor profiles may prove to be of value for individualizing the treatment of disseminated carcinoid tumour disease.

Immunohistochemical localization of acidic fibroblast growth factor in normal human enterochromaffin cells and related gastrointestinal tumours

Acidic fibroblast growth factor (aFGF) is a member of the structurally related heparin-binding growth factor family. The best studied members of this family are aFGF and basic FGF (bFGF), which are potent mitogens and differentiation factors for mesoderm-derived cells, including fibroblasts. This study was designed to verify the immunohistochemical expression of aFGF in normal human endocrine cells of the gut and in related endocrine tumours. We examined normal gastrointestinal mucosa from seven different subjects and 41 gut endocrine tumours from different sites, including stomach, duodenum, and small and large intestine, using an aFGF polyclonal antibody with no cross-reactivity for bFGF. We localized aFGF in a fraction of serotonin-producing enterochromaffin (EC) cells of the normal gut, while it was absent in gastrin (G), CCK, secretion (S), somatostatin (D) and glicentin (L) cells. aFGF immunoreactivity was also expressed in serotonin producing EC cell tumours, but not in other functional types of gut endocrine neoplasms investigated, including gastric ECL cell, duodenal somatostatin and gastrin cell, and rectal L cell tumours. A positive correlation was found between expression of aFGF and the amount of tumour fibrous stroma, suggesting that aFGF may be involved in proliferation and activity of stromal fibroblasts.

Vascular endothelial growth factor (VEGF) expression in prostatic tumours and its relationship to neuroendocrine cells

Vascular endothelial growth factor (VEGF) expression was examined by immunohistochemistry in 45 prostatic carcinoma specimens and ten benign prostatic tumours (BPH). The majority of carcinoma specimens exhibited cytoplasmic staining for VEGF and showed a trend of increasing expression with dedifferentiation (2p = 0.003). Immunoreactive VEGF was also seen in the prostatic carcinoma cell lines, the order of staining intensity was PC3 > DU145 > LNCaP. Intense granular cytoplasmic staining for VEGF was observed in neuroendocrine-like cells which were seen focally in many of the prostatic specimens. Consecutive sections were incubated with a chromogranin A antibody to confirm the neuroendocrine phenotype of these cells. A significant correlation (P < 0.0001) between the total number of intensely stained VEGF-positive cells and chromogranin A-positive cells was found. A subpopulation of neuroendocrine-like cells also showed intense immunoreactivity for transforming growth factor alpha (TGF-alpha). A correlation was observed (2p = 0.0092) between the intensity of VEGF and TGF-alpha immunostaining in carcinoma cells which were not of neuroendocrine differentiation. The presence of these two angiogenic factors may aid the neovascularisation of carcinomas and their increased expression in tumour-associated neuroendocrine cells may contribute to a more aggressive phenotype.

Are enterochromaffinlike cell tumours reversible? An experimental study on gastric carcinoids induced in Mastomys by histamine2-receptor blockade

A rapid induction of enterochromaffinlike (ECL) cell tumours has been shown in Praomys (Mastomys) natalensis subjected to histamine2-receptor blockade. In the present study the reversibility of ECL cell proliferation induced by acid inhibition was investigated. Short-term treatment (8 weeks) with the histamine2-receptor antagonist loxtidine caused a moderate hypergastrinemia, accompanied by a minor increase in histamine contents and a 2-fold increased volume density of the endocrine cells in gastric oxyntic mucosa. Eight weeks after withdrawal of treatment the volume density of endocrine cells was normalised as were the tissue levels of histamine, indicating a total reversibility of ECL cell hyperplasia. Long-term treatment (24 weeks) caused severe changes in the endocrine cell population of the oxyntic mucosa with neoplasia (5/21), dysplasia (11/21) and nodular hyperplasia (5/21). The endocrine cell density increased twofold and tissue histamine levels fourfold. 24 weeks after cessation of treatment, the endocrine cell density had decreased to 136% of controls, while histamine concentrations were normalised. The frequency of invasive carcinoids after recovery (4/23) differed only slightly from that seen after treatment for 24 weeks (5/21). Dysplastic lesions were only seen in 1/23 and hyperplastic lesions were of less severe type after recovery. The results demonstrate that ECL cell hyperplasia and dysplasia, induced by acid inhibition, are reversible after cessation of treatment. However, ECL cell tumours did not disappear, within the given observation period. One may therefore speculate that ECL cell proliferation is no longer reversible once the neoplastic (transformed) phenotype has developed.

Expression of transforming growth factor alpha and its receptor in human neuroendocrine tumours

Transforming growth-factor-alpha (TGF-alpha) is a 50-amino-acid polypeptide that binds to the epidermal growth factor (EGF) receptor and stimulates cell growth. It has been suggested that enhanced production of TGF-alpha and EGF receptors by tumour cells promote tumour-cell growth by autocrine mechanisms. In the present study we have investigated the expression of TGF-alpha and EGF receptors in human neuroendocrine tumours, including midgut carcinoid tumours, phaeochromocytomas and medullary thyroid carcinomas. TGF-alpha expression was demonstrated in biopsies of all tumours examined (n = 30) and EGF receptors in a majority of tumours by Northern analysis and/or immunocytochemistry. Expression of TGF-alpha and EGF receptors was also demonstrated in primary cultures of tumour cells. Carcinoid tumours and phaeochromocytomas in culture secreted detectable amounts of TGF-alpha into the culture medium (400-700 pM). The amount of secreted TGF-alpha could be suppressed by octreotide treatment in individual tumours. Administration of exogenous TGF-alpha stimulated carcinoid tumour growth in vitro as determined by the DNA contents of cell cultures. The growth-stimulatory effect of TGF-alpha could be partially blocked by the use of neutralizing anti-EGF receptor monoclonal antibodies (MAbs). In conclusion, several human neuroendocrine tumours express both TGF-alpha and EGF receptors in in vivo and in vitro, suggesting that TGF-alpha may regulate tumour-cell growth by autocrine mechanisms.

Tumors of the endocrine/neuroendocrine system: an overview

For the sake of discussion, the markedly diversified tumors of the endocrine/neuroendocrine system are classified as those originating in classic epithelial endocrine organs (eg, adrenal cortical adenomas), from the diffuse endocrine cells (eg, jejunal carcinoid tumors), or from clusters of these cells (eg, islet cell tumors); and those arising from neurosecretory neurons (eg, neuroblastoma) or paraganglia (eg, carotid body tumor). Although traditional transmission electron microscopy is useful for identifying neurosecretory or endosecretory granules as such, with few exceptions (eg, insulin-containing granules with a complex paracrystalline core) it is not possible to ascribe a granule type (size, shape, or ultrastructure) to a distinct nosologic entity or secretory product because of their overlapping fine structures in different cell types. Immunoelectron microscopy methods utilizing colloidal gold-labeled secondary antibodies can be used to localize virtually any antigen (peptide or neuroamine) to a specific neurosecretory or endosecretory granule or other cell structure. General endocrine/neuroendocrine cell markers such as neuron-specific enolase, the chromogranins, and synaptophysin are useful in identifying neuroendocrine differentiation in a neoplasm using routine immunohistochemical procedures. The current relevance of the APUD concept of Pearse as well as the biologic importance of endocrine/neuroendocrine secretory products such as bombesin and insulinlike growth factors also are discussed.

Insulin-like growth factor mediated stromal-epithelial interactions in human breast cancer

The prominent 'desmoplastic' or stromal reaction seen in many invasive breast carcinomas lead to early speculation that stromal cells play a role in breast cancer pathogenesis. Experimental evidence now supports this hypothesis and interactions between stromal cells and epithelial cells appear to be important for both normal mammary development and neoplasia. The identification of genes that are selectively expressed in the stroma of malignant breast lesions has recently provided new insights into the molecular basis of stromal-epithelial interactions. Stromally expressed genes include growth factors, proteases and extracellular matrix proteins, all biological activities with potential roles in malignant progression. Investigations discussed here concern the nature of the paracrine signals provided by malignant epithelial cells that activate changes in stromal gene expression, the effect that the stromally derived factors have on the behavior of malignant epithelial cells and the identification of novel factors and receptors in either stroma or epithelia that contribute to their mutual interactions. These questions will be addressed in the context of this laboratory's studies on insulin-like growth factors, as these molecules show marked differences in stromal expression between benign and malignant breast tissue and thus provide a useful paradigm for investigations into the paracrine environment of an evolving breast tumor.

Growth factors and carcinoid tumours

The presence of growth factors and their receptors in human midgut carcinoids and in gastric carcinoids of Mastomys have been investigated. Human midgut carcinoid tumours produce IGF-I as demonstrated by immunocytochemistry and radioimmunoassay. IGF-I receptors were detectable in half of the tumours and stimulation of cultured tumour cells with IGF-I enhanced DNA synthesis. IGF-I may therefore act as an autocrine stimulator of carcinoid tumour growth. Expression of TGF-alpha and EGF-receptors could also be demonstrated in midgut carcinoids by immunocytochemistry and Northern analysis, suggesting that TGF-alpha participates in the autocrine modulation of carcinoid growth. Co-culture of human midgut carcinoid tumours and rat fetal cholinergic neurons demonstrated secretion of a potent neuronotrophic factor by cultured tumour cells. IGF-I and TGF-alpha may account for these neuronotrophic effects, but carcinoid tumours may also secrete an as yet unidentified growth factor. Gastric (ECL cell) carcinoids developed rapidly in Mastomys during hypergastrinemia due to histamine2-receptor blockade, suggesting that gastrin is an essential growth factor for these carcinoids.