Increased expression of CD44v6 in endocrine pancreatic tumours but not in midgut carcinoid tumours

Multilayered heterogeneity as an intrinsic hallmark of neuroendocrine tumors

Neuroendocrine tumors (NETs) comprise a complex and highly heterogeneous group of neoplasms that can arise all over the body, originating from neuroendocrine cells. NETs are characterized by a general lack of symptoms until they are in advanced phase, and early biomarkers are not as available and useful as required. Heterogeneity is an intrinsic, pivotal feature of NETs that derives from diverse causes and ultimately shapes tumor fate. The different layers that conform NET heterogeneity include a wide range of distinct characteristics, from the mere location of the tumor to its clinical and functional features, and from its cellular properties, to the core signaling and (epi)genetic components defining the molecular signature of the tumor. The importance of this heterogeneity resides in that it translates into a high variability among tumors and, hence, patients, which hinders a more precise diagnosis and prognosis and more efficacious treatment of these diseases. In this review, we highlight the significance of this heterogeneity as an intrinsic hallmark of NETs, its repercussion on clinical approaches and tumor management, and some of the possible factors associated to such heterogeneity, including epigenetic and genetic elements, post-transcriptional regulation, or splicing alterations. Notwithstanding, heterogeneity can also represent a valuable and actionable feature, towards improving medical approaches based on personalized medicine. We conclude that NETs can no longer be viewed as a single disease entity and that their diagnosis, prognosis and treatment must reflect and incorporate this heterogeneity.

Close correlation between beta-catenin gene alterations and nuclear accumulation of the protein in human hepatocellular carcinomas

Several lines of evidence indicate that beta-catenin acquires oncogenic activity when its intracellular concentration increases as a result of either mutation in the beta-catenin gene itself or inactivation of the adenomatous polyposis coli (APC) gene. In an attempt to elucidate the molecular mechanisms underlying hepatocellular carcinogenesis, we have studied the frequency of beta-catenin gene alterations in exon 3, a region known to represent a mutation hot spot, and its inappropriate protein expression by immunohistochemistry in 73 hepatocellular carcinomas (HCCs). The results were correlated with different clinical and pathological data, particularly with the presence or not of an associated cirrhosis. Fourteen (19%) HCCs showed beta-catenin gene alterations with missense mutations in nine cases and interstitial deletions in five cases. These genetic alterations were present in both cirrhotic and non-cirrhotic groups. By contrast, we did not find any beta-catenin gene alterations in the nine fibromellar carcinomas we examined. Nuclear accumulation of the protein was observed in 18 of them (25%). Remarkably, these included ten of the 14 tumors harboring somatic mutations in the beta-catenin gene (P < 0.001). Our results indicate that accumulation of beta-catenin resulting from genetic mutations is a frequent event in non-fibrolamellar type hepatocellular carcinoma. The close association between increased beta-catenin protein stability and mutation indicates that immunohistochemistry may be a powerful method for the detection of the mutated protein in future clinical practice.

Comparative genomic hybridization analysis of sporadic neuroendocrine tumors of the digestive system

Little information is available on the molecular mechanisms underlying neuroendocrine tumorigenesis. To obtain an overview of the genomic imbalances characterizing these tumors, we studied 20 benign or malignant sporadic endocrine gastroenteropancreatic tumors by comparative genomic hybridization. Chromosomal imbalances were found in all tumors. Gains of chromosomal material were more frequent than losses. The most frequent gains were of chromosomes and chromosome arms 5 (55%), 14 (55%), 17q (55%), and 7 (50%). Losses were most frequent from 11q (30%) and 16p (30%). Gains of chromosome 5 did not occur in nonmetastatic tumors, whereas losses of 9p were observed exclusively in intestinal tumors. In addition, we found two high-level amplifications, of 17q11-21 and 19q13. A complementary FISH analysis revealed that the gain in 17q11-21 included amplification of the protooncogene HER2/neu. As in multiple endocrine neoplasia type-1-associated tumors, deletions of chromosome band 11q13 appear to be involved in the development of sporadic digestive tract neuroendocrine tumors, but our results suggest that other chromosomal regions are also involved.

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.

Regulation of endothelial CD44 expression and endothelium-tumour cell interactions by hepatocyte growth factor/scatter factor

Cancer metastasis involves the passage of tumour cells into and out of blood or lymphatic circulatory systems and requires their interaction with the endothelial cells lining these vessels. Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional protein that enhances tumour cell motility and extracellular matrix invasion and has been implicated as a mediator of metastasis. In this study, we have investigated the effect of HGF/SF on tumour cell-endothelial cell interactions. A fluorescent tumour cell-endothelial cell attachment assay demonstrated that, following endothelial monolayer stimulation with HGF/SF, tumour cell attachment to endothelium is increased. Addition of anti-CD44 antibodies in this assay inhibited the effects of HGF/SF. Western blotting studies showed that HGF/SF increased expression of the adhesion molecule CD44 in endothelial cells. These results were confirmed by both immunohistochemical staining and a cell-surface adhesion molecule ELISA. These results suggest that HGF/SF plays a key role in the initial adhesion mechanism between tumour cells and endothelial cells via up-regulation of CD44.