Endocrine cell hyperplasia and appendiceal carcinoids

Appendiceal Well-Differentiated Neuroendocrine Tumors: A Single-Center Experience and New Insights into the Effective Use of Immunohistochemistry

Background. Appendiceal well-differentiated neuroendocrine tumor is the most common histological type of appendiceal tumor. The majority of tumors are found incidentally at the tip of the appendix, with few exceptions. Due to its primarily indolent nature, this entity presents unique pathological challenges, particularly in the appropriate use of immunohistochemistry which this study aims to clarify. Patients and methods. Patients diagnosed at University Health Network (Canada) between 2005–2019 were selected and reviewed. Results. We identified 70 patients and sex distribution was female 60%; median age 36.5 years. Among them, 63 patients underwent appendectomy, and seven had initial right hemicolectomy for non-appendix lesions. Mean tumor size was 5.0 mm. Tumor extent was submucosa (15%); muscularis propria (34%); subserosa or mesoappendix (42%); visceral peritoneum (8%). All were clinically non-functional and negative for nodal and distant metastasis. Ninety percent of tumors were WHO Grade 1; 10% were WHO Grade 2. Immunohistochemically, an average of six stains were performed per patient. Nearly all tumors were positive for chromogranin A, synaptophysin, CAM5.2, and CDX2. MIB-1 staining was < 3% in 58/63 tumors. Other immunohistochemical stainings performed were hormonal markers (serotonin, glucagon, pancreatic peptide, peptide YY). Subsequent right hemicolectomy was performed on five patients. All were followed up (median 4 years 8 months), and all were alive without recurrence except for one patient who died of another comorbidity. Conclusion. Tumors that are small, localized, and of low grade can be reasonably exempt from an extensive immunohistochemical panel in the absence of non-typical clinical and morphological features.

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.

Pathologic classification and clinical behavior of the spectrum of goblet cell carcinoid tumors of the appendix

Appendiceal tumors exhibiting both neuroendocrine and glandular differentiation are uncommon and have caused difficulty in pathologic classification, prediction of prognosis, and clinical management. Previously, such lesions have been variously designated as adenocarcinoid, goblet cell carcinoid (GCC), and mixed adenocarcinoma carcinoid. In this study, we undertook a retrospective investigation of 63 such cases and classified them as typical GCC (group A) and adenocarcinoma ex GCC on the basis of the histologic features of the tumor at the primary site. The adenocarcinoma ex GCC group was further divided into signet ring cell type (group B) and poorly differentiated adenocarcinoma type (group C). The clinical characteristics and prognosis were compared within these groups and with conventional de novo appendiceal adenocarcinomas. Both groups A and B tumors shared a similar immunoprofile, which included generally focal immunoreactivity for neuroendocrine markers, and a normal intestinal type mucin glycoprotein profile (negative MUC1 expression and preserved MUC2 immunoreactivity). The proliferative index was relatively low in these tumors and slightly increased from groups A to B tumors (11% to 16%). Both beta-catenin and E-cadherin exhibited a normal membranous staining pattern in groups A and B tumors. The poorly differentiated adenocarcinomas ex GCC (group C) demonstrated abnormal p53 and beta-catenin immunoreactivity. The mean follow-up time was 49+/-5 (SE) months. The overall disease-specific survival for all subtypes was 77%, with 46% of patients without evidence of disease and 31% alive with disease. The mean survival was 43+/-7 months. All the patients with clinical stage of I or IIA disease had a favorable outcome after appropriate surgery with or without chemotherapy. Although most patients (63%) with GCC presented at an advanced clinical stage, their clinical outcome could be differentiated by subclassification of tumors. The stage IV-matched 5-year survival was 100%, 38%, and 0% for groups A, B, and C, respectively. In conclusion, GCC is a distinctive appendiceal neoplasm that exhibits unique pathologic features and clinical behavior. They display a spectrum of histologic features and possess the potential to transform to an adenocarcinoma phenotype of either signet ring cell or poorly differentiated adenocarcinoma types. Careful evaluation of the morphologic features of GCCs and appropriate pathologic classification are crucial for clinical management and prediction of outcome. Surgical management with right hemicolectomy is recommended after appendectomy for most cases, particularly those with an adenocarcinoma component (groups B and C).

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.

Endocrine tumours of the gastrointestinal tract-selected topics

This review provides an update on the pathogenesis and histopathological diagnosis of endocrine tumours of the gastrointestinal tract, concentrating on three different varieties whose careful assessment by pathologists is of particular clinical significance. These are the four types of enterochromaffin-like cell tumour of the gastric corpus, the periampullary somatostatin-containing D-cell tumour of the duodenum, and the frequently chromogranin A-negative L-cell tumour of the appendix and large intestine. In addition, the value of pathological factors in predicting the behaviour of gastrointestinal endocrine tumours and selecting therapy is discussed, and the crucial role of the pathologist in the multidisciplinary team management of these neoplasms is emphasized.

Neuroendocrine tumors of the appendix

The vast majority of neuroendocrine neoplasms of the appendix are carcinoid tumors. Most are of enterochromaffin (EC) cell type, although rare examples are of L cell type. EC cell carcinoids of the appendix differ from those encountered elsewhere in the gastrointestinal system. For example, they are remarkably common given the small size of the appendix, are usually benign, occur in younger patients, and typically contain sustentacular cells that express S-100. Origin from subepithelial neuroendocrine cells could explain these characteristics. It has also been suggested that most appendiceal carcinoids are hyperplastic rather than neoplastic, although this hypothesis requires further study. Nevertheless, truly neoplastic EC cell carcinoids of the appendix undoubtedly occur, and those greater than 2 cm in diameter have a significant risk of producing distant metastases. Carcinoid syndrome is a very rare presentation. Tubular carcinoids are unusual benign neoplasms; it has been proposed that they represent L cell carcinoids with a predominant tubular pattern of growth. Goblet cell carcinoids tend not to produce a grossly visible tumor mass but diffusely infiltrate the wall. They typically exhibit tight clusters of goblet cells, usually with scattered neuroendocrine cells and sometimes with Paneth cells, sometimes surrounding a small lumen. They may behave as a low-grade malignancy. The distinction between goblet cell carcinoid and other types of tumor is of great importance because of the implications for treatment and prognosis. Frank adenocarcinoma can arise from goblet cell carcinoids, and tumors with both components are classified as mixed goblet cell carcinoid-adenocarcinoma. The carcinoma component of the latter determines their prognosis, which would be worse than for a goblet cell carcinoid alone.

Morphological-histochemical study of intestinal carcinoids and K-ras mutation analysis in appendiceal carcinoids

Intestinal carcinoids are potentially malignant neoplasms. Their histogenesis and pathogenesis are currently uncertain. The morphological and histochemical characteristics of twenty intestinal carcinoids are studied. The primary sites of three mucin-producing tumors were examined by electron microscope. Furthermore 11 appendiceal carcinoids were analysed by the polymerase chain reaction (PCR) for the detection of ras and p53 point mutations. Microscopically all carcinoids were of mixed type. Focal mucin production was evident in three carcinoids that metastasised to regional lymph nodes. HID-Alcian blue staining proved that mucin in both primary and secondary foci did not belong to the sulphated group. The secretory granules and mucin droplets found in a single neoplastic cell suggest that carcinoids of the small intestine and some of the appendix arise from the endoderm. Neither ras nor p53 mutations were detected. It seems that ras oncogenes are probably not involved in the pathogenesis of appendiceal carcinoids.

Dual carcinoid/epithelial neoplasia of the appendix

We report a series of 13 lesions of the human vermiform appendix in which a carcinoid component was associated with a separate non-carcinoid epithelial component that included an adenoma-like lesion of the mucosal epithelium. We use the term dual carcinoid/epithelial neoplasia to describe this phenomenon. The carcinoid component was insular/trabecular in nine cases, tubular in one case and of goblet cell type in three. The epithelial component was a mucinous cystadenoma in four, a mucinous tumour of uncertain malignant potential in three, and a mucinous cystadenocarcinoma in six. No intermediate cell population was seen and in three cases the carcinoid and epithelial components were in different parts of the appendix, leading us to suggest that these lesions may be true 'collision' tumours in which two neoplasms have arisen in the same organ. The prognosis appears to be no worse than for either of the components alone, but conclusions regarding these lesions must be guarded on account of their rarity and the small numbers available for study.

A comparative immunohistochemical study of jejunoileal and appendiceal carcinoids. Implications for histogenesis and pathogenesis

BACKGROUND

The purpose of this study was to determine the histogenesis of jejunoileal and appendiceal carcinoids and to ascertain whether this could be useful in further explaining the pathology of these neoplasms.

METHODS

Eight cases each of multiple jejunoileal carcinoids and appendiceal carcinoids together with their respective age-matched and sex-matched controls were stained with silver stains, chromogranin A, serotonin, and S-100. Histomorphometric evaluations of the endocrine cells in the mucosa adjacent to the carcinoids were carried out and compared with the respective controls using the Student's t test.

RESULTS

All the carcinoids from both groups stained for argyrophilia, argentaffinity, chromogranin A, and serotonin. Histomorphometric evaluations showed intraepithelial endocrine cell hyperplasia (IECH) in the jejunoileal carcinoid group (P = 0.007, chromogranin; P = 0.004, serotonin) but not in the appendiceal carcinoid group. On the other hand, subepithelial endocrine cell aggregates that were separate from the main tumor were seen in two cases of appendiceal carcinoids. With S-100, all appendiceal carcinoids showed intrinsic tumor positivity whereas the jejunoileal carcinoids did not.

CONCLUSIONS

The finding of IECH with multiple jejunoileal carcinoids suggests that these carcinoids arise from a field effect. The absence of IECH with appendiceal carcinoids as well as their association with subepithelial endocrine cell aggregates and their intimate relationship with Schwann cell processes suggests that appendiceal carcinoids arise from a more discrete unit, the subepithelial neuroendocrine complex.

The histogenesis of appendiceal carcinoid tumours

Twenty-two appendiceal carcinoid tumours, comprising 10 classical carcinoids, six tubular carcinoids and six goblet cell carcinoids were examined by histochemistry and immunohistochemistry. All of the tumours showed evidence of neuroendocrine differentiation. Classical carcinoids were invariably intimately associated with S-100 protein positive cells, supporting an origin from sub-epithelial neuroendocrine cells. Both tubular and goblet cell carcinoids expressed cytoplasmic mucin and immunoglobulin A, and neither were associated with S-100 protein positive cells. These observations suggest that tubular and goblet cell carcinoids are derived from epithelial crypt stem cells.

The topographical and age distributions of neuroendocrine cells in the normal human appendix

In order to clarify the histogenesis of appendiceal carcinoid tumours, epithelial (ENC) and subepithelial (SNC) neuroendocrine cells were counted at four sites in 50 normal appendices stained by standard argyrophil and argentaffin techniques. In general, ENC were present in similar number at all sites within the appendix, whereas SNC were more numerous at the tip than at the base. The number of ENC was similar throughout life, apart from an increase in one neonate and some elderly patients, whereas SNC were maximal in young adults. Thus, the topographical and age distributions of SNC, but not those of ENC, parallels the topographical and age incidence of appendiceal carcinoid tumours, suggesting that most appendiceal carcinoid tumours arise from SNC rather than ENC.