The role of immunohistochemistry, electron microscopy, and ultrastructural cytochemistry in the diagnosis of mixed carcinoma-neuroendocrine neoplasms

Endocrine secretory granule production is caused by a lack of REST and intragranular secretory content and accelerated by PROX1

Endocrine secretory granules (ESGs) are morphological characteristics of endocrine/neuroendocrine cells and store peptide hormones/neurotransmitters. ESGs contain prohormones and ESG-related molecules, mainly chromogranin/secretogranin family proteins. However, the precise mechanism of ESG formation has not been elucidated. In this study, we experimentally induced ESGs in the non-neuroendocrine lung cancer cell line H1299. Since repressive element 1 silencing transcription factor (REST) and prospero homeobox 1 (PROX1) are closely associated with the expression of ESG-related molecules, we edited the REST gene and/or transfected PROX1 and then performed molecular biology, immunocytochemistry, and electron and immunoelectron microscopy assays to determine whether ESG-related molecules and ESGs were induced in H1299 cells. Although chromogranin/secretogranin family proteins were induced in H1299 cells by knockout of REST and the induction was accelerated by the PROX1 transgene, the ESGs could not be defined by electron microscopy. However, a small number of ESGs were detected in the H1299 cells lacking REST and expressing pro-opiomelanocortin (POMC) by electron microscopy. Furthermore, many ESGs were produced in the REST-lacking and PROX1- and POMC-expressing H1299 cells. These findings suggest that a lack of REST and the expression of genes related to ESG content are indispensable for ESG production and that PROX1 accelerates ESG production.

Trial registration: Not applicable.

Electron Microscopic Study Using Formalin-fixed, Paraffin-embedded Material, with Special Reference to Observation of Microbial Organisms and Endocrine Granules

In the diagnostic pathology practice, specimens for electron microscopy (EM) are not necessarily handled and fixed under the ideal condition. In the present article, the author describes ultrastructural study using formalin-fixed and/or paraffin-embedded material. The fine morphologic preservation is often acceptable, particularly when small cubes are dug out of paraffin blocks. Particulate structures such as neuroendocrine granules and microbes are consistently observed even using paraffin sections. Paraffin sections signalized with silver particles in Grimelius and Grocott stains or diaminobenzidine products in immunostaining and in situ hybridization are applicable to EM evaluation by using a pre-embedding sequence. The practical merit includes the targeted approach: highly accurate sampling from focal lesions can be achieved for EM analysis, after observing hematoxylin and eosin-stained or specific-signalized paraffin-sections. This allows us pathologists a convenient and practical way for identifying focally infected pathogens, as well as a retrospective ultrastructural analysis of rare lesions long kept as a form of paraffin blocks.

[Mixed endocrine tumors]

Mixed endocrine tumors are tumors composed of at least two distinct tumor populations, one of which is endocrine. Because of their rarity and unusual presentation, endocrine mixed tumors raise many problems of diagnosis, management and therapy. Three main types of endocrine mixed tumors are recognized: The existence of these various types has been confirmed by recent molecular studies, even if the same studies have also shown that the histogenesis of a mixed endocrine tumor cannot be predicted from its histological features. Composite tumors are the less rare mixed tumors. The recent WHO classification recommends to restrict the term of composite endocrine tumor to the epithelial tumors containing at least 30% of obviously tumoral endocrine cells; some authors recommend to use higher thresholds, of at least 50%, in order to avoid overdiagnosis. The endocrine component is usually well differentiated, easily identified by its suggestive histological features; the endocrine nature of tumor cells is confirmed by the immunodetection of specific endocrine and neuro-endocrine markers (such as chromogranin A and synaptophysin). In some cases, the endocrine component is poorly differentiated: the demonstration of neuro-endocrine markers is necessary to confirm the diagnosis. Mixed tumors can occur in every anatomical site; they are more frequent in organs containing endocrine cells in the normal state (especially the digestive tract and the pancreas), but they can also be observed in organs devoid of endocrine cells (such as the mammary gland). The management of mixed endocrine tumors must take into account the more aggressive component. Mixed tumors containing a well differentiated endocrine component and an adenocarcinomatous component are to be treated like adenocarcinomas. Mixed tumors containing a poorly differentiated endocrine component must be considered as poorly differentiated endocrine carcinomas.

Neuroendocrine carcinomas: role of immunocytochemistry and electron microscopy

Neuroendocrine tumors occur in many sites of the body and can present significant diagnostic problems when poorly differentiated. To identify a tumor as neuroendocrine, pathologists commonly use either immunocytochemistry or electron microscopy. In this report, the various immunocytochemical reagents are reviewed along with the ultrastructural features of neuroendocrine tumors. Site-specific variations in neuroendocrine tumors are discussed. A cost-effectiveness evaluation was performed on tumors from one laboratory which showed that electron microscopy was a less expensive diagnostic modality if more than three antibodies were necessary to arrive at the correct pathological diagnosis.

Use of the uranaffin reaction in the identification of neuroendocrine granules

This overview emphasizes the utility of the uranaffin reaction in the diagnosis of tumors derived from neuroendocrine cells. The history, cell organelle specificity, tissue specificity, pH requirements, and detailed procedure of the uranaffin reaction is provided. Uranaffin-positive granules are also identified within the NS granules of the stem cell paraneuron (archiparaneuron) of coelenterates, and a hypothetical evolutionary scheme depicting the possible origins of the key biochemical features of the advanced mammalian NS granule is included. The role of nucleotides, a major component of true NS granules, is discussed. A possible intragranular function of ATP as a regulator of osmotic pressure and the extracellular physiologic effects of secreted intragranular nucleotides are discussed in some detail.

Composite gastric carcinoma and precursor lesions with amphicrine features in chronic atrophic gastritis

A composite carcinoma of the gastric body consisting of endocrine and mucous epithelial cells with interspersed amphicrine cells is reported together with ultrastructural and immunocytochemical documentation of endocrine and nonendocrine differentiation. The tumor was associated with hypergastrinemia related to chronic atrophic gastritis (achlorhydria) and with multiple proliferative lesions, such as intramucosal microcarcinoid (IMC) and endocrine cell proliferations of the micronodular and linear type, which are currently regarded as carcinoid precursor changes. Ultrastructurally, a composite architecture with amphicrine features was demonstrated in the primary tumor, IMC, and liver metastases. On the other hand, the endocrine cell proliferations exclusively contained gastrin and enterochromaffinlike cells. Immunostaining with antibodies to calcitonin documented a number of positive cells both in the primary and in the metastatic sites. This is the first report of mixed exocrine-endocrine-amphicrine components both in a metastasizing carcinoma and in its precursor lesions in a chronic hypergastrinemic state. Unlike previously reported lesions, the endocrine component was unexpectedly composed of calcitonin cells, which are not usually present in the gastric mucosa.

Neuroendocrine carcinoma of the stomach with extensive somatostatin immunoreactivity

Upper gastrointestinal tract neuroendocrine tumors producing predominantly somatostatin have thus far been described only in the duodenum; their characteristic features include the frequent presence of psammoma bodies (psammomatous somatostinomas), and the association with von Recklinghausen's neurofibromatosis. Gastric neuroendocrine tumors, on the other hand, tend to display immunoreactivity to serotonin but may include small subpopulations producing gastrin, motilin, pancreatic polypeptide, and somatostatin. In this report we describe a neuroendocrine carcinoma of the stomach with rapidly fatal outcome, displaying neurosecretory granules by electron microscopy and immunoreactivity to pan-neuroendocrine markers, ie, chromogranin and neuron-specific enolase. The only neuroendocrine regulatory peptide detected in the tumor was somatostatin, identified by immunohistochemistry in the majority of neoplastic cells. In contrast with duodenal somatostinomas, there were no psammoma bodies and no demonstrable association with von Recklinghausen's neurofibromatosis. To our knowledge this appears to be the first report of a malignant neuroendocrine tumor with diffuse somatostatin immunoreactivity.

Upper abdominal neoplasms: an introduction and selected references

The organs in the upper half of the abdominal cavity can give rise to a highly heterogeneous collection of neoplasms that encompasses a broad spectrum of clinical features, light microscopic appearances, immunostaining properties, and fine structure. Because of the anatomic proximity of the viscera in this region, the differential diagnosis of an upper abdominal mass may include consideration of tumors that arise from the stomach, duodenum, liver, kidney, adrenal, and pancreas. There are many distinctive ultrastructural features among the various tumors that can be used effectively by the diagnostic electron microscopist, but it is also important to take into account the considerable overlap in fine structure that occurs among different tumors and among similar tumors from different organs. In the session on upper abdominal neoplasms, the electron microscopic characteristics of the common tumors of each viscus were reviewed before the presentation of individual case studies that incorporated original observations and illustrated some unusual entities. The selection of cases that follows is inevitably small and arbitrary, but the cases demonstrate the contribution that electron microscopy can make in the study of an upper abdominal mass and illustrate some of the similarities that can be encountered among tumors of different organs.

Moderately differentiated neuroendocrine carcinoma of the larynx. A clinicopathologic study of 54 cases

Fifty-four cases of primary laryngeal moderately differentiated neuroendocrine carcinoma from the Armed Forces Institute of Pathology Otolaryngic Tumor Registry (AFIP-OTR) are reported. The tumors most often present in men in their sixth and seventh decades of life and are heralded by an array of symptoms, the most frequent being hoarseness. The primary site was most often the supraglottic larynx. The investigation has included light-microscopic, histochemical, immunocytochemical, and electron microscopic analyses which support expression of both neuroendocrine and epithelial differentiation. Conservative surgery alone can be utilized if early identification of the tumor and complete surgical removal are assured. The follow-up of the patients reveals 62% as remaining tumor-free after surgical extirpation over periods ranging from 1 month to 16 years (median: 3 years, 9 months). Factors adversely affecting prognosis include metastatic disease at initial presentation, incomplete surgical removal, and vascular or lymphatic invasion. There was no correlation between tumor size, morphologic pattern, mitoses or necrosis, and survival. Sixty-eight percent of the patients gave a history of long-term cigarette smoking. The classification and pathogenesis of these neoplasms remains the focus of much speculation. They are suggested as arising from the cells of the dispersed neuroendocrine system (DNES). However, a more uniform and descriptive nomenclature is necessary. This study resolves this and other issues along with a presentation of clinicopathologic data of the tumor entity.

Neuroendocrine tumors of the gastrointestinal tract

Neoplastic proliferations of neuroendocrine cells (NE) may occur throughout the entire GI tract but affect particularly appendix and ileum ("midgut carcinoids"), rectum ("hindgut carcinoids"), as well as stomach and the duodenum ("foregut carcinoids"). Only more exceptionally, they arise in the esophagus, jejunum and colon. The NE tumors encompass a heterogeneous gross and microscopic structural spectrum, ranging from inconspicuous microproliferations ("mucous membrane nevi") to bulky tumor masses. Their growth patterns are usually characteristic and easily recognized. In doubtful cases their NE differentiation becomes established by a characteristic silver affinity, by the ultrastructurally observed presence of characteristic "endocrine" secretion granules, and by immunohistochemically detectable occurrence of "pan-NE markers" (neuron-specific enolase, chromogranins, and synaptophysin), biogenic amines (mainly serotonin), and neurohormonal peptides. Foregut carcinoids usually contain serotonin, gastrin, and somatostatin, midgut carcinoids often only serotonin and tachykinins, whereas the hindgut carcinoids as a rule are multihormonal with a wide spectrum of hormonal peptides, including even insulin. Most GI NE tumors are found in the appendix (50%) and the ileum (30%). Practically all (98%) of the appendiceal NE tumors are benign. They have recently been proposed as arising from apparently Schwann-cell-related NE cells in the submucosa, whereas the ileal--and probably also all the other non-appendiceal NE tumors--are derived from the totipotential cells in epithelial crypts of the mucosa. Among the ileal NE neoplasms a large number can metastasize and result in a fatal outcome. The ability to metastasize is related to the size and to the multiplicity of the primary tumors at the time of initial diagnosis and, to some extent, to their histopathologic growth pattern. Now, some relationship between the prognosis and the cytochemically assessed nuclear DNA content of the NE tumor cells has also been established; not less than about 1/4 to 1/3 seem to be aneuploid. Almost 90% of the rectal carcinoids are benign. Exceptionally, a highly malignant NE neoplasms can arise from the colon/rectum--as well as from the esophagus--composed of NE cells of small and intermediate size. The NE tumors of the stomach are often composed of ECL (enterochromaffin-cell-like) cells; such ECL cell carcinoids are related to atrophic gastritis with pernicious anemia; experimentally, they can be induced by hypergastrinemia in rats. Duodenal carcinoids often contain psammoma bodies and can be associated with neurofibromatosis.