Enteroendocrine cell hyperplasia, carcinoid tumours and adenocarcinoma in long-standing ulcerative colitis

Age-related changes in polycomb gene regulation disrupt lineage fidelity in intestinal stem cells

Tissue homeostasis requires long-term lineage fidelity of somatic stem cells. Whether and how age-related changes in somatic stem cells impact the faithful execution of lineage decisions remains largely unknown. Here, we address this question using genome-wide chromatin accessibility and transcriptome analysis as well as single-cell RNA-seq to explore stem-cell-intrinsic changes in the aging Drosophila intestine. These studies indicate that in stem cells of old flies, promoters of Polycomb (Pc) target genes become differentially accessible, resulting in the increased expression of enteroendocrine (EE) cell specification genes. Consistently, we find age-related changes in the composition of the EE progenitor cell population in aging intestines, as well as a significant increase in the proportion of EE-specified intestinal stem cells (ISCs) and progenitors in aging flies. We further confirm that Pc-mediated chromatin regulation is a critical determinant of EE cell specification in the Drosophila intestine. Pc is required to maintain expression of stem cell genes while ensuring repression of differentiation and specification genes. Our results identify Pc group proteins as central regulators of lineage identity in the intestinal epithelium and highlight the impact of age-related decline in chromatin regulation on tissue homeostasis.

Microcarcinoid and Ulcerative Colitis: Case Report and Literature Review

Gastrointestinal microcarcinoid tumors are rare, and the concomitant diagnosis of microcarcinoid tumor and inflammatory bowel disease is even rarer. A 54-year-old African American male with an eight-year history of ulcerative colitis (UC) presented with a three-day history of abdominal pain and bloody diarrhea. Rectal biopsy on colonoscopy was notable for small nests of neuroendocrine cell proliferation in the mucosa consistent with a diagnosis of microcarcinoid tumor. Whether the incidence is coincidental or represents an epiphenomenon of chronic inflammation remains to be determined.

Incidence of composite intestinal adenoma-microcarcinoid in 158 surgically resected polyps and its association with squamous morule

Composite intestinal adenoma-microcarcinoid (CIAM) is a rare colorectal lesion consisting of adenoma and small well-differentiated neuroendocrine cell clusters at its base. Its incidence is unknown. Benign squamous morule may demonstrate a neuroendocrine phenotype by immunohistochemistry. We investigated the incidence and clinicopathologic features of CIAM in endoscopically unresectable, surgically removed colorectal adenomas and evaluated its association with squamous morule. Archived pathology materials from 158 surgically resected colorectal adenomas were reviewed. 139 (88%) polyps were entirely submitted for microscopic examination. All lymph nodes were negative for adenocarcinoma and neuroendocrine tumor. CIAM was identified in 6 (3.8%) cases. The microcarcinoid (MC) was distributed over a mean of 5.8 mm (range < 1 to 12 mm), and was multifocal in 5 cases. The MC component was positive for synaptophysin in 6, CK5/6 in 4, and β-catenin in 3 cases. Two of 6 (33.3%) CIAM showed concurrent squamous morule, compared to 4.0% (6 of 152) of adenomas without MC (p < 0.05). At the end of the mean follow-up of 53 months, 4 were free of disease and one patient with previous history of pulmonary large cell neuroendocrine carcinoma (NEC) had a recurrence of NEC. One patient died of an unrelated disease. The incidence of CIAM in surgically removed colorectal adenomas is 3.8%, with an indolent clinical course. Frequent co-expression of CK5/6 and β-catenin in MC combined with common co-existence of squamous morule in the same polyp suggests shared pathogenesis of MC in CIAM and squamous morule, likely representing altered Wnt/β-catenin signaling pathway.

Enteroendocrine cells-sensory sentinels of the intestinal environment and orchestrators of mucosal immunity

The intestinal epithelium must balance efficient absorption of nutrients with partitioning commensals and pathogens from the bodies' largest immune system. If this crucial barrier fails, inappropriate immune responses can result in inflammatory bowel disease or chronic infection. Enteroendocrine cells represent 1% of this epithelium and have classically been studied for their detection of nutrients and release of peptide hormones to mediate digestion. Intriguingly, enteroendocrine cells are the key sensors of microbial metabolites, can release cytokines in response to pathogen associated molecules and peptide hormone receptors are expressed on numerous intestinal immune cells; thus enteroendocrine cells are uniquely equipped to be crucial and novel orchestrators of intestinal inflammation. In this review, we introduce enteroendocrine chemosensory roles, summarize studies correlating enteroendocrine perturbations with intestinal inflammation and describe the mechanistic interactions by which enteroendocrine and mucosal immune cells interact during disease; highlighting this immunoendocrine axis as a key aspect of innate immunity.

Sigmoid colon carcinoma with focal neuroendocrine differentiation associated with ulcerative colitis: A case report

INTRODUCTION

Neuroendocrine tumors of the colon and rectum are relatively rare compared to sporadic colorectal carcinoma. There are few reports of neuroendocrine tumors of the colon and rectum in patients with ulcerative colitis.

PRESENTATION OF CASE

A patient with sigmoid colon carcinoma with focal neuroendocrine features is presented. A 32-year-old man, who had been followed for ulcerative colitis for 14 years, was found to have carcinoma of the sigmoid colon on routine annual colonoscopy, and he underwent laparoscopic total colectomy. Pathologic examination showed sigmoid colon adenocarcinoma with focal neuroendocrine features.

DISCUSSION

Most colorectal carcinomas associated with inflammatory bowel disease are histologically similar to the sporadic type, and tumors with neuroendocrine features are very unusual.

CONCLUSION

Very rare case of sigmoid colon carcinoma with neuroendocrine features arising in a patient with UC was described.

Inflammation Meets Metabolic Disease: Gut Feeling Mediated by GLP-1

Chronic diseases, such as obesity and diabetes, cardiovascular, and inflammatory bowel diseases (IBD) share common features in their pathology. Metabolic disorders exhibit strong inflammatory underpinnings and vice versa, inflammation is associated with metabolic alterations. Next to cytokines and cellular stress pathways, such as the unfolded protein response (UPR), alterations in the enteroendocrine system are intersections of various pathologies. Enteroendocrine cells (EEC) have been studied extensively for their ability to regulate gastrointestinal motility, secretion, and insulin release by release of peptide hormones. In particular, the L-cell-derived incretin hormone glucagon-like peptide 1 (GLP-1) has gained enormous attention due to its insulinotropic action and relevance in the treatment of type 2 diabetes (T2D). Yet, accumulating data indicate a critical role for EEC and in particular for GLP-1 in metabolic adaptation and in orchestrating immune responses beyond blood glucose control. EEC sense the lamina propria and luminal environment, including the microbiota via receptors and transporters. Subsequently, mediating signals by secreting hormones and cytokines, EEC can be considered as integrators of metabolic and inflammatory signaling. This review focuses on L cell and GLP-1 functions in the context of metabolic and inflammatory diseases. The effects of incretin-based therapies on metabolism and immune system are discussed and the interrelation and common features of metabolic and immune-mediated disorders are highlighted. Moreover, it presents data on the impact of inflammation, in particular of IBD on EEC and discusses the potential role of the microbiota as link between nutrients, metabolism, immunity, and disease.

The intestinal immunoendocrine axis: novel cross-talk between enteroendocrine cells and the immune system during infection and inflammatory disease

The intestinal epithelium plays a crucial role in maintaining barrier function and immune homeostasis, a failure of which results in disease. This review focuses on the epithelial enteroendocrine cells and the crosstalk that exists with immune cells during inflammation.

The intestinal epithelium represents one of our most important interfaces with the external environment. It must remain tightly balanced to allow nutrient absorption, but maintain barrier function and immune homoeostasis, a failure of which results in chronic infection or debilitating inflammatory bowel disease (IBD). The intestinal epithelium mainly consists of absorptive enterocytes and secretory goblet and Paneth cells and has recently come to light as being an essential modulator of immunity as opposed to a simple passive barrier. Each epithelial sub-type can produce specific immune modulating factors, driving innate immunity to pathogens as well as preventing autoimmunity. The enteroendocrine cells comprise just 1% of this epithelium, but collectively form the bodies’ largest endocrine system. The mechanisms of enteroendocrine cell peptide secretion during feeding, metabolism and nutrient absorption are well studied; but their potential interactions with the enriched numbers of surrounding immune cells remain largely unexplored. This review focuses on alterations in enteroendocrine cell number and peptide secretion during inflammation and disease, highlighting the few in depth studies which have attempted to dissect the immune driven mechanisms that drive these phenomena. Moreover, the emerging potential of enteroendocrine cells acting as innate sensors of intestinal perturbation and secreting peptides to directly orchestrate immune cell function will be proposed. In summary, the data generated from these studies have begun to unravel a complex cross-talk between immune and enteroendocrine cells, highlighting the emerging immunoendocrine axis as a potential target for therapeutic strategies for infections and inflammatory disorders of the intestine.

Histogenesis and natural history of gut neuroendocrine tumors: present status

Important progress has been made during the last decade in the histopathologic characterization and overall prognostic evaluation of gut neuroendocrine tumors. However, some issues like tumor histogenesis, typing, functional characterization, and preferred site of origin deserve further clarification. This is a survey of the present status of the matter outlining some of the open points. In particular, careful comparison of normal gut endocrine cell types with related endocrine tumors so far identified shows an unexplained lack of neoplasms involving upper small intestine cells like secretin, cholecystokinin, motilin, and GIP cells, as well as the equally unexplained concentration of serotonin EC cell tumors in the ileum and appendix or of somatostatin cell tumors in the duodenal papillary region, despite their wide distribution in the normal gut, not to mention gastrinomas arising in the pancreas, normally devoid of gastrin cells. Special functional (e.g., achlorhydria-driven hypergastrinemia) or pathologic (as chronic inflammation) conditions may locally influence the proliferative and differentiation state of the endocrine cells thus promoting tumor growth. Tumor histologic structure, differentiation level, and proliferative index as well as gastrointestinal wall barriers to tumor diffusion may account for most prognostic parameters, with considerable changes, however, according to the tumor type and site. Thus, further work is needed to develop tumor- and site-adjusted prognostic parameters.

Precursor lesions of endocrine system neoplasms

The concept of precursor lesions of endocrine neoplasms is a new and interesting topic in endocrine pathology. A variety of clinicopathological conditions are associated with a sequence of cellular changes from hyperplasia to neoplasia; dysplasia is, in contrast, quite rare. The majority of precursor lesions is associated with familial genetic syndromes. These include C-cell hyperplasia in thyroid that is associated with familial medullary thyroid carcinoma, adrenal medullary hyperplasia as a precursor of phaeochromocytomas in MEN2 syndrome, rare pituitary adenohypophyseal cell hyperplasia in familial syndromes associated with pituitary adenomas, MEN1-related precursor gastric enterochromaffin-like cell (ECL) hyperplasia, and duodenal gastrin producing (G) and/or somatostatin producing (D) cell hyperplasia that give rise to type II gastric neuroendocrine tumours (NETs) and duodenal NETs, respectively, and MEN1- or VHL-related islet hyperplasia, islet dysplasia and ductulo-insular complexes that are associated with pancreatic NETs. Other hyperplasias are not thought to be associated with genetic predisposition. Some are attributed to inflammation; autoimmune chronic atrophic gastritis-related ECL hyperplasia can progress to type I gastric NETs, and EC (enterochromaffin) cell or L cell hyperplasia associated with inflammatory bowel diseases can progress to colorectal NETs. In the lung, diffuse idiopathic pulmonary neuroendocrine cell hyperplasia can give rise to peripherally-located low grade pulmonary NETs and tumourlets (neuroendocrine microtumours <5  mm). Rarely, secondary hyperplasias develop into autonomous neoplasms, as in tertiary hyperparathyroidism or pituitary thyrotroph adenomas in primary hypothyroidism. While some precursor lesions, such as thyroid C cell hyperplasia, represent frankly premalignant conditions, others may represent a sequence of proliferative changes from hyperplasia to benign neoplasia that may also progress to malignancy.

Colorectal neuroendocrine carcinomas and adenocarcinomas share oncogenic pathways. A clinico-pathologic study of 12 cases

OBJECTIVE

Neuroendocrine carcinomas (NECs) are rare neoplasms with an increasing incidence. Oncogenetic pathways of colorectal NEC are still poorly understood, and no treatment standards are available for these rare tumors.

METHODS

We analyzed retrospectively the clinical records and histology of 12 patients with colorectal NEC. KRAS and BRAF mutations were investigated after the dissection of exoendocrine and neuroendocrine components. ALK alterations and EML4-ALK transcripts were detected by in-situ hybridization and determination of fusion transcripts, respectively.

RESULTS

At the time of diagnosis, the mean age of the patients was 60 years (40-79) and 10 patients had synchronous metastases. A transient response occurred in two patients and one patient treated with cisplatin-etoposide or fluoropyrimidine-oxaliplatin, respectively. Tumor progression-related death occurred in 11 of 12 patients. Ten tumors contained an exocrine component, accounting for 5-70% of the tumor, and the other two contained an amphicrine component. BRAF/KRAS mutations were found in six of 10 tumors, corresponding to BRAF(V600E) (n=2) or KRAS(G12D) (n=2), KRAS(G12V) or KRAS(G13D). DNA was obtained from both exocrine and endocrine components in seven cases, and the BRAF/KRAS status was identical in all cases. Split of the ALK locus was detected in a minority of tumor cells in two of eight cases, but EML4-ALK transcripts were absent.

CONCLUSION

The association of an exocrine component in all cases and the similar profile of BRAF/KRAS mutations indicate that colorectal NEC may correspond to a high-grade transformation of colorectal carcinoma. New chemotherapy regimens using targeted therapies should be assessed in these tumors.

Pathology of gastrointestinal disorders

Nonneoplastic and neoplastic proliferative lesions of endocrine cells of the gastrointestinal tract are detailed. A multistep continuum from hyperplasia, dysplasia to neoplasia is identified for histamine-producing enterochromaffin-like (ECL) cells of the gastric corpus. Most gastric neuroendocrine tumors (NETs) are silent and composed by ECL cells, the second most frequent neuroendocrine neoplasms being the high-grade neuroendocrine carcinoma (NEC). In the duodenum, preneoplastic lesions are similarly described for gastrin (G) and somatostatin (D) cells. G-cell NETs are the most frequent neuroendocrine tumors of the duodenum, either functioning or nonfunctioning, followed by D-cell NETs and gangliocytic paraganglioma (GCP). No systematic definition of nonneoplastic lesions exists for endocrine cells of the ileum, appendix, and colon-rectum. The most frequent ileal NETs are serotonin-producing enterochromaffin (EC)-cell NETs (classic carcinoid), associating with functional syndrome only in presence of liver metastases. Neoplasms are usually larger in the colon as compared with the small lesions observed in the rectum. High-grade NECs are observed in the colon and rectum-sigmoid, often associate with nonendocrine neoplastic components, and fare an aggressive course with poor outcome and short survival.

Pathology of Gastrointestinal Neuroendocrine Tumors: An Update

Gastrointestinal (GI) neuroendocrine tumors (NETs) are a heterogeneous group of relatively slow-growing neoplasms with marked site-specific differences in hormonal secretion and clinical behavior. Most are sporadic neoplasms, with only 5% to 10% arising in patients with hereditary disorders, most commonly in multiple endocrine neoplasia type 1. Although a uniform terminology is not universally accepted, use of the 4-category WHO classification of these tumors is becoming more widespread, and recommendations for tumor grading and staging have been recently formulated. Most GI NETs are easily recognized on routine histologic examination; rarely, a limited panel of immunohistochemical markers may be useful in establishing the diagnosis. This article describes general and site-specific features of these tumors and outlines potential pitfalls in diagnosis.

Pathologic research update of colorectal neuroendocrine tumors

Colorectal neuroendocrine tumors (NETs) originate from neuroendocrine cells in the intestinal tract, and represent a small area within oncology, but one which has provided increasing new data during the past years. Although the World Health Organization has determined clinical and histological features to predict prognosis for such tumors, they may not be valid on an individual basis. We aim to give an overview of the recent findings with regard to pathology, molecular genetics and diagnosis of NETs.

Synchronous colitic cancers and microcarcinoids in a patient with long-standing and extensive ulcerative colitis: a case report and review of the literature

We report a case of colitic cancer detected by target biopsies at surveillance colonoscopy in a patient with long-standing and extensive ulcerative colitis. At first, the detected colitic cancer was removed by endoscopic mucosal resection as the patient refused surgical resection. However, total proctocolectomy with an ileal-J-pouch anal anastomosis was performed additionally after informed consent had been obtained from the patient, as the resected specimen included invasive cancer histologically. Surprisingly, histologic examination of the surgical specimens revealed another flat invasive colitic cancer and 2 microcarcinoids, which were not detectable by preoperative colonoscopy or by macroscopic investigation of the surgically resected specimen. The occurrence of carcinoid in patients with ulcerative colitis has been reported only sporadically. In addition, coexistence of colitic cancer and carcinoids is extremely rare. Cases of this rare combination reported previously in the English literature are summarized and discussed.

Endocrine hyperplasia and dysplasia in the pathogenesis of gastrointestinal and pancreatic endocrine tumors

Non-neoplastic proliferative lesions of endocrine cells have been described throughout the gastrointestinal tract and pancreas. A multistep continuum from hyperplasia and dysplasia to neoplasia originally was identified and systematically defined for histamine-producing enterochromaffin-like (ECL) cells of the gastric corpus. More recently, a similar classification system was devised for gastrin (G)- and somatostatin (D)-producing cells in the duodenum. Preneoplastic lesions of the endocrine pancreas still lack a solid and widely accepted definition of a multistep growth process. Similarly, in spite of reports of carcinoid-associated endocrine cell hyperplasia, there is no systematic definition of nonneoplastic lesions of the endocrine cells of the ileum, appendix and colorectum.

An unusual case of colonic mixed adenoendocrine carcinoma: collision versus composite tumor. A case report and review of the literature

We report a case of collision tumor of the cecum in a 50-year-old woman and discuss the morphological criteria used for classifying mixed glandular-endocrine neoplasms of the digestive tract in a large series of reported cases. The cecal tumor showed clear geographic polarization, with no admixture or transition of the 2 neoplastic components. A lymph nodal metastatic deposit contained both tumors. Immunohistochemical stainings were consistent with the carcinomatous and carcinoidal nature of the 2 neoplasms, except for a minute area of carcinoembryonic antigen positivity in the carcinoid. A review of the literature shows that many mixed glandular-endocrine tumors of the digestive tract escape precise classification using established morphological criteria. Collision and composite tumors can share common histological and immunohistochemical features, including polyclonal metastases and carcinoembryonic antigen expression in the carcinoidal area. Mixed tumors of the cecum showing a collision-like morphology appear to behave more aggressively than other colonic adenoendocrine carcinomas.

Solitary microcarcinoid of the rectal stump in ulcerative colitis

A case of solitary microcarcinoid and chronic ulcerative colitis of the rectal stump is described. The association of intestinal carcinoid with ulcerative colitis has been reported previously in 26 patients. Pathogenic pathways are discussed according to the presence of multifocal carcinoid and/or gut endocrine cell hyperplasia.

Multiple microcarcinoids in a patient with long standing ulcerative colitis

A male patient with a 17 year history of intractable ulcerative colitis of the entire type was treated by total proctocolectomy. Colonoscopy before surgery did not identify dysplasia. Histological examination of the resected colorectum revealed that, in addition to chronic inflammatory infiltrates, there were 21 areas of microcarcinoids located in the muscularis propria and in the superficial layer of the submucosa. Carcinoids may be more common than previously thought, and they may be a reactive phenomenon to a variety of factors in ulcerative colitis.

Coexisting carcinoid tumors in familial adenomatous polyposis-associated upper intestinal adenomas

Upper gastrointestinal polyps and extraintestinal tumors are well recognized in association with familial adenomatous polyposis (FAP). Although carcinoid tumors have been reported in association with sporadic colonic neoplasms and ulcerative colitis, to date, carcinoids have not been reported in association with FAP. We report a patient with FAP who has recurrent carcinoid tumors located at the bases of duodenal adenomas. The genetic basis of carcinoid neoplasms is still uncertain. This report may represent the clinical effect of the APC gene mutation on the enterochromaffin cell line manifesting as recurrent carcinoid tumors in physical association with intestinal adenomas. Future genetic analysis and epidemiological studies may be of value in determining whether a true association exists.

Crohn's disease associated with pellagra and increased excretion of 5-hydroxyindolacetic acid

A 47-year-old woman with seronegative polyarthritis, diarrhea, and photosensitivity dermatitis was found to have Crohn's disease and pellagra. The presence of high values of 5-hydroxyindolacetic acid in the urine began the exhaustive investigations and finally enterotomy. No mass lesion was found. Argyrophilic cells were not increased in areas of inflamed intestinal mucosa or the normal mucosa. The disagreement between biochemical and histologic findings was attributed to sampling error. Antiinflammatory treatment for Crohn's disease was given and the gastrointestinal and articular symptoms improved, excretion of 5-hydroxyindolacetic acid returned to normal and there was no relapse of pellagra. Pellagra as a complication of Crohn's disease has been described in 4 cases; malnutrition and intestinal malabsorption were the proposed mechanisms for the niacin deficiency and pellagra of those patients. In the current case, the pathogenesis of pellagra may be accounted to wastage of tryptophan by an increased pool of intestinal argyrophilic cells, suggested by increased urinary excretion of 5-hydroxyindolacetic acid.

Carcinoid tumour complicating inflammatory bowel disease. A study of two cases with review of the literature

Two cases of carcinoid tumour complicating inflammatory bowel disease (IBD) are presented. Both tumours were located in the appendiceal tip. The first case occurred in a man with Crohn's disease (CD), and the second one in a woman suffering from ulcerative colitis (UC). Histochemical and immunohistochemical studies were not allowed on case 1 because the tumour was not still present on serial sections of the appendix. On case 2, tumour cells were not reactive with Grimelius and Masson-Fontana stainings, but were strongly stained with anti-keratin and anti-chromogranin monoclonal antibodies (MAb), and faintly expressed neuron specific enolase (NSE), and Leu-7. Both cases occurred in inflammatory or damaged mucosa which exhibited Paneth cell metaplasia and hyperplasia and areas indefinite for dysplasia. Along with these lesions, hyperplasia of enteroendocrine cells was pointed out in the neighbouring appendiceal and colonic mucosa by means of anti-chromogranin MAb. These data suggest that the association of carcinoid tumour with IBD, albeit rare, is not coincidental and is the result of hyperplastic and dysplastic troubles that may involve enteroendocrine cells as well as such other derivatives of digestive stem cells as columnar cells, goblet cells and Paneth cells.

Mixed adenocarcinoma/carcinoid tumour of large bowel in a patient with Crohn's disease

A 50 year old woman with a 20 year history of Crohn's disease underwent laparotomy which revealed extensive disease in the small and large bowel, and this was resected. Gross examination of the resected bowel showed features of Crohn's disease as well as a polypoid tumour in the caecum. Histopathological examination of the tumour showed it to be an infiltrating mixed adenocarcinoma/carcinoid tumour arising in a tubulovillous adenoma. Random sampling of the rest of the bowel affected by Crohn's disease also showed a focus of dysplasia and adenomatous change. It is suggested that Crohn's disease may have played a part in the pathogenesis of the tumour.

Depletion of neuroendocrine cells in rectal biopsy specimens from HIV positive patients

AIMS

To compare the density of neuroendocrine cells in rectal biopsy specimens from human immunodeficiency virus (HIV) infected individuals with that of a control group.

METHODS

Neuroendocrine cells in rectal biopsies were identified using an immunohistochemical stain for chromogranin and subsequently quantified using a method of linear intercept.

RESULTS

Neuroendocrine cells were found to be significantly decreased in the HIV positive group.

CONCLUSIONS

Loss of neuroendocrine cells may contribute to apoptotic bodies seen in this condition. This could be related to infection of these cells with HIV and could contribute to diarrhoeal disease in HIV infection.

Carcinoid tumors and inflammatory bowel disease

Three cases are described in which carcinoid tumors arose in previously established inflammatory bowel disease: two were in the ileum in cases of Crohn's disease, and one was in the rectum in a case of ulcerative colitis. Review of this association in the literature suggests that it may be more than fortuitous.

Endocrine cell hyperplasia and appendiceal carcinoids

As endocrine tumours in a number of organs may arise in a background of hyperplasia, the density of endocrine cells in appendices from ten patients with carcinoid tumours was compared with that in appendices from ten age- and sex-matched control patients. Crypt and lamina propria endocrine cells were quantified separately. The density of argentaffin endocrine cells in the crypts was significantly higher in appendices with carcinoid tumours when compared with the controls. No difference was found in non-argentaffin endocrine cells, and no difference was found in either argentaffin or argyrophil endocrine cells in the lamina propria. While it is possible that carcinoid tumours induce an increase in the number of enterochromaffin (EC) cells in the background mucosa, it is considered more likely that EC cell hyperplasia predisposes to the development of carcinoid tumours of the appendix.