Grades of atypia in tubular and villous adenomas of the human colon. An electron microscopic study

Quantitative electron microscopic study on grades of atypia in adenomas of the human large bowel

Clarification of the ultrastructural features of the three different grades of histologic atypia of adenomas (i.e., mild, moderate, and severe atypia) with reference to carcinoma of the human colon and rectum was undertaken using electron microscopic quantitative analysis. Ten normal epithelia, 36 adenomas (14 with mild atypia, 13 with moderate atypia, and 9 with severe atypia) and 14 carcinomas (well-differentiated adenocarcinoma) were examined with light and electron microscopes. Although it has been generally accepted that malignant transformation of an adenoma gradually proceeds with increasing atypia, using light microscopy, ultrastructural quantitative analysis clearly revealed that fine features of individual atypia did not correspond with histologic grades of atypia. Ultrastructural changes occurred abruptly in moderate atypia and showed similar cellular characteristics to carcinoma cells. Mild atypia was almost similar in appearance to normal epithelial cells. Striking changes in the moderate atypic cells were plane apposition of the cell membrane, decrease of the desmosomes, and increase of the lysosomes. These atypical cells were assumed to play a significant role in the adenoma-carcinoma sequence. Therefore, radical surgical therapy would be required for moderate atypic adenoma of the large bowel that is difficult to remove endoscopically.

Localization of villin, a cytoskeletal protein specific to microvilli, in human ileum and colon and in colonic neoplasms

Villin is a cytoskeletal protein of microvilli of epithelial cell brush borders found principally in absorptive cells of the intestine and proximal renal tubule. A marker of both enterocyte differentiation and epithelial cell polarity, it has been studied mainly in experimental animals. We raised monoclonal antibodies to villin and used them to localize it in human ileum and colon and in 22 colonic neoplasms. Villin is localized in the brush border of normal ileum and in the luminal border of normal colon and is expressed with increasing staining intensity as cells migrate from crypt to surface. It was present in the luminal border in all five adenomas and in 16 of 17 adenocarcinomas studied. In addition, villin staining was observed in the cytoplasm of 10 tumors, and in the basement membrane area surrounding tumor in 10 cases. In "transitional" mucosa adjacent to carcinomas it was confined to the luminal border. Abnormal expression of villin by a significant proportion of colonic tumors suggests that it may have a role as a marker of colorectal neoplasia.

Histochemistry of small intestinal dysplasia in familial polyposis coli

Biopsies of duodenal and ileal mucosa from patients with familial polyposis coli were studied. Areas of atypia were identified in the duodenum of six patients and in the ileum of three patients. Grade I atypia was characterized by crowding and elongation of cells and nuclei, a slight reduction in the number of goblet cells and the presence of a brush border; grade II atypia was further characterized by pseudo- or pluristratification of cells, a marked reduction in the number of goblet cells and the absence of a brush border. In areas of atypia, columnar cells often contained PAS-positive apical granules, which were diastase-resistant and unstained by alcian blue at any pH; the brush border, even where recognizable in haematoxylin-eosin and PAS-stained sections, was unreactive histochemically for alkaline phosphatase. Goblet cells were few in areas of atypia, but those present were regularly stained by PAS and alcian blue pH 2.6. Apical granules, similar in their histochemical characteristics to those observed in columnar cells in areas of atypia, were also found in otherwise normal mucosal areas, even in some patients with no overt areas of atypia in the biopsies studied. These granules have been interpreted as an abnormality, possibly preceding the onset of atypia. Hyperplasia of goblet cells, secreting mucins with the same staining pattern as in normal intestine, was found in some patients, either adjacent to areas of atypia or independent of them. Intervening columnar cells had a normal morphology, alkaline phosphatase-reactive brush borders and no sign of mucus secretion. This goblet cell hyperplasia has been interpreted as a reactive, nonspecific alteration of the mucosa.

Tumor dedifferentiation: an important step in tumor invasion

Tumor invasion in vivo was studied by light and electron microscopy as well as by immunofluorescence microscopy. Special regard was paid to the grade of tumor differentiation. Dimethylhydrazine-induced murine colonic carcinomas comprising a differentiated and an undifferentiated tumor type with low and high invasiveness respectively, were used. At the invasion front of both tumor types a striking dissociation of the organized tumor cell complexes into isolated tumor cells was found together with a loss of most of the cytological features of differentiation. It is supposed that this process mobilizes the tumor cells from the main tumor bulk enabling them to invade the host tissue by active locomotion. This view is strongly supported by the demonstration of morphological equivalents of active cell movement such as pseudopodia-like cytoplasmic extrusions, adaptive changes of the cell shape and microfilament bundles. Although the proposed mechanism of tumor invasion is essentially the same in both tumor types, the grade of differentiation is nevertheless critical, as in the undifferentiated carcinomas only subtle dedifferentiation steps (loss of basement membrane and cell junctions) are necessary to acquire an invasive status. This fact may explain the comparatively high invasiveness and poor prognosis of undifferentiated carcinomas.

Mechanisms of tumor invasion: evidence from in vivo observations

The major mechanisms of tumor invasion in vivo are discussed in the present review. A special emphasis is placed on tumor dedifferentiation which has proved to be of paramount importance for the invasion process. Based on in vivo observations obtained from various human and animal tumors a concept for the mechanism of tumor invasion is proposed which mainly comprises the following basic events: the first and essential step in tumor invasion is the tumor dedifferentiation and dissociation at the invasion front. This apparently temporary and reversible process mobilizes the tumor cells out of the main tumor bulk and enables them to invade the host tissue by active locomotion. This mechanism is essentially supported by an interstitial edema in the host tissue adjacent to the tumor periphery, which causes an 'opening and widening' of the host intercellular spaces. Enzymatic changes in the micromilieu of the extracellular matrix may contribute to this process. The tumor cell proliferation completes the invasion process in so far, as the invading tumor cells are still able to proliferate, leading this way to expanding tumor cell nests in the host tissue which have the potency to redifferentiate. The expansive growth of these tumor cell nests results in a progressive atrophy of the host tissue, mainly caused by an increasing compression and a competitive withdrawal of oxygen and other nutrients by the tumor cells. The overall picture of tumor invasion can therefore be considered as a repetitive cycle of active tumor cell locomotion followed by focal tumor cell proliferation in the host tissue.

Sequential cellular changes during chemical carcinogenesis

Phenotypically altered, preneoplastic cell populations were detected by micromorphological and cytochemical methods in a number of tissues treated with various chemical carcinogens. Further cellular analysis of carcinogenesis has shown that different cellular phenotypes follow each other during tumor development. Thus, stages of the neoplastic transformation leading from preneoplastic to early and advanced neoplastic cells can be observed directly. The cellular changes preceding the various tumor types suggest that cytologically different neoplasms have also a different cytogenesis. The identification of putative preneoplastic and early neoplastic cell populations by morphological and cytochemical methods allows for the first time the dissection and subsequent detailed investigation of target cells of chemical carcinogens that are at high risk of becoming cancer cells. Recent results of the cytochemical and biochemical microanalysis of preneoplastic hepatocytes support the concept that the well-known aberration of carbohydrate metabolism in tumor cells might occur in response to a carcinogen-induced metabolic derangement, which frequently appears to be associated with an excessive storage of polysaccharides or lipids persisting for weeks and months until fast-growing tumors develop. The increasing reports on the appearance of hepatic tumors in humans suffering from inborn hepatic glycogenosis agree with this hypothesis. Whereas the cause of the persisting storage phenomena is most probably fixed at the genetic level, epigenetic changes, namely an adaptation of cellular enzymes gradually activating alternative metabolic pathways, might be responsible for the ultimate neoplastic transformation of the cell.

Electron microscopic study of adenocarcinoma of the small bowel associated with Crohn's disease

"Crohn's Carcinoma" of a 34-year-old patient is presented in this paper. The fine structure of the tumour is discussed in detail, because there have been no previous reports of electron microscopic studies of this tumour. The adenocarcinoma cells were electron microscopically less differentiated than expected on the basis of light microscopic examinations. In the tumor cells, several round dense granules were observed. Similar granules were also described in the cells of intestinal type gastric and colon cancers, being considered a sign of pathologic mucus secretion. In a part of the tumour cells, intracisternal parallel tubular inclusions were seen like those described in malignant melanoma and osteosarcoma. In the dysplastic small-bowel mucosa adjacent to the tumour, the maturation disorder of the epithelial cells was similar to changes described in the precancerous states of the colon.

Immunohistochemical evaluation of carcinoembryonic antigen, secretory component, and epithelial IgA in tubular and villous large-bowel adenomas with different grades of dysplasia

In a material of 513 consecutively collected large-bowel polyps, tubular and villous adenomas with corresponding histologic grades of epithelial dysplasia were selected. Fifty-two samples of the former and 27 of the latter category were evaluated semiquantitatively for immunohistochemical staining of the epithelial marker proteins carcinoembryonic antigen (CEA), secretory component (SC), and IgA. No consistent differences in the overall staining properties were found between the two types of tumours. In both categories the staining intensity for SC and epithelial IgA decreased with increasing degree of dysplasia, most strikingly so for IgA. This observation shows that the malignant alterations impair the capacity of the columnar epithelium to produce SC and to express it as a functional receptor mediating uptake of dimeric IgA. Thus, the absence of epithelial IgA in large-bowel adenomas may be a useful adjunct in grading of dysplasia. Conversely, the presence of CEA did not seem to be related to dysplastic alterations in the epithelium.

Electron microscopic study of carcinoma of the colon

During electron microscopic studies of 24 carcinomas of the colon the authors compared the ultrastructural characteristics of tumorous epithelial cells of various degrees of differentiation. Beside the epithelial elements, the myofibroblast reaction, considered to be a local immune reaction due to invasive tumour cells, observable in the stroma of tumours was also treated in detail. It was observed that myofibroblasts develop from the fibroblasts of the matrix of colonic mucosa.