Flat adenoma-adenocarcinoma sequence in the colon of rats

Flat elevated lesions of the colon and rectum: a spectrum of neoplastic and nonneoplastic entities

The aim of this prospective study is to establish the frequency and the type (neoplastic and nonneoplastic) lesions defined endoscopically as flat elevated lesion (FEL) in the colon and rectum, as well as to compare flat adenomas (FAs) to polypoid lesions of the same size with morphometric and immunohistochemical analysis. One hundred nineteen patients were studied through fibrocolonoscopy with chromoscopy (indigo carmine spray). All detected lesions (total of 195) were removed, and FELs measuring 10 mm or smaller were also selected. Using histopathologic criteria, they were divided in neoplastic (adenomas and carcinomas) and nonneoplastic ones. In neoplastic lesions, the following parameters were evaluated to compare FAs with polypoid lesions: morphometric studies with Index of Structural Atypia (ISA) and Stratification Index (SI), evaluation of cellular proliferation with label index of Ki-67, and expression of p53 protein. Of 195 lesions resected, only 33 (17%) met the endoscopic requirements for FELs. Twelve (36.4%) were neoplastic and 21 (63.6%) considered nonneoplastic. Among the FAs, there were a percentage of high-grade (severe dysplasia) significantly more frequent than observed in polypoid lesions (16.7% vs 2.6%). In addition, the SI, Ki-67 label index and p53 positivity were significantly higher in FAs. The ISA also reached significant differences between both groups of adenomas. Non-neoplastic FELs included different entities such as hyperplasic polyps, focuses of colitis, normal mucosa, and scars. The endoscopic elements analyzed were shared between nonneoplastic FELs and FAs. A central depression, when air was properly insufflated, considered typical in neoplastic lesions, was frequently observed in nonneoplastic lesions. Following the endoscopic criteria of FELs, nonneoplastic lesions predominated over the adenomatous lesions, demonstrating that FELs and FAs are not homologous terms. The frequency of high-grade dysplasia was significantly more elevated in the adenomatous FELs than in polypoid adenomas. The ISA, SI, p53 expression, and Ki-67 label index were helpful in differentiating adenomatous FELs from polypoid lesions. Flat elevated lesions selected by endoscopic criteria are, in fact, a heterogeneous population of lesions.

Prevalence and distinctive biologic features of flat colorectal adenomas in a North American population

BACKGROUND & AIMS

To assess the prevalence of flat and depressed (F&D) colorectal adenomas in the United States, we performed a prospective study of 211 American patients.

METHODS

Dye-assisted colonoscopy was performed in the presence of both an American and a Japanese investigator.

RESULTS

F&D lesions were found in 22.7% of patients, and these were more likely to be adenomatous than polypoid lesions (82% vs. 67%; P = 0.03) and contained more invasive cancer (4.5% vs. 0%; P = 0.04), which also appeared to be at a disproportionately advanced stage. The average size of all F&D advanced lesions (high-grade dysplasia and cancer) was significantly smaller than comparable polypoid lesions (10.75 +/- 2.7 mm vs. 20 +/- 2.9 mm; P < 0.05). F&D adenomas showed significantly stronger fragile histidine triad (FHIT) expression and lower p53 reactivity than similarly sized polypoid adenomas, whereas proliferative and apoptotic indices were similar in both groups.

CONCLUSIONS

We conclude that there is a significant prevalence of colonic F&D colorectal adenomas in this country and that these lesions have significantly different biologic features than polypoid lesions. The clinical and epidemiologic implications of these findings for American patients need to be addressed in further studies.

Are dietary fiber-induced alterations in colonic epithelial cell proliferation predictive of fiber's effect on colon cancer?

Alterations in cell proliferation of the colon have been observed as a result of changes in amount and type of dietary fiber and in relation to risk of developing colon cancer. Although some human observational and intervention studies contribute to the database, most information results from experiments on rodents. Because of numerous contradictory reports linking dietary fiber, cell proliferation, and colon cancer, we undertook a critical review of existing methods in an attempt to explain the inconsistencies. Although there may be some individual types of dietary fiber that protect against chemically induced colon cancer, dietary fiber as a single entity does not appear to afford any consistent protection. Because of significant differences in experimental protocols among laboratories, it is not yet possible to state with certainty that increases in cell proliferation, induced by fiber consumption, are predictive of increased tumorigenesis. Much of what has been observed and interpreted as elevation of risk may simply be normal homeostatic changes in cell proliferation. Even though fermentation to short-chain fatty acids is a mechanistically attractive hypothesis to explain why fiber modulates cytokinetics, data do not consistently support short-chain fatty acids as biological intermediates in risk of colon cancer. The state of the art in this field has not yet progressed to the point where a clear effect of dietary fiber on cytokinetics and colon carcinogenesis can be assessed with any degree of certainty. Additional markers of apoptosis, differentiation, and cell-cell communication may be required for a more accurate analysis of the relation among fiber, cytokinetics, and colon cancer.

ras p21 Isoprenylation inhibition induces flat colon tumors in Wistar rats

PURPOSE

The effect of pravastatin, an inhibitor of ras p21 isoprenylation, on the gross type of colon tumors induced by azoxymethane was investigated in Wistar rats.

METHODS

Rats received ten weekly subcutaneous injections of 7.4 mg/kg body weight of azoxymethane and intraperitoneal injections of 10 or 20 mg/kg body weight of pravastatin every other day until the end of the experiment at Week 45.

RESULTS

Administration of pravastatin at both dosages had no significant effect on the incidence of colon tumors but significantly increased the incidence of rats with adenomas only. In contrast to the elevated adenomas in control rats, flat adenomas were significantly more prevalent in rats given pravastatin. Pravastatin at both doses significantly decreased the labeling index, but not the apoptotic index, of elevated adenomas, whereas it significantly decreased the labeling index but increased the apoptotic index of flat adenomas. Administration of pravastatin at both dosages also significantly decreased the amounts of membrane-associated ras p21 in colon tumors.

CONCLUSIONS

These findings suggest that the ras oncogene may be closely related to the development of adenocarcinomas from adenomas and the development of elevated or polypoid tumors of the colon.

Non-polypoid adenomas of the colon are associated with subjacent lymphoid nodules. An experimental study in rats

BACKGROUND

Subjacent lymphoid nodules (SLNs) have been found in 38% of non-polypoid colonic adenomas in humans. In the present work the presence of SLNs in experimentally induced colonic adenomas was investigated in rats.

METHODS

1,2-Dimethylhydrazine was injected subcutaneously in 290 Sprague-Dawley rats for 27 weeks.

RESULTS

An SLN was present in 28.6% of the 84 adenomas, in 8.4% of the 119 adenocarcinomas, and in 9.7% of the 31 small carcinomas without remnant adenomatous tissue. An SLN was found in 35.6% of the 59 non-polypoid neoplasias but only in 9.1% of the 175 polypoid (that is, exophytic) neoplasias. When only adenomas were considered, SLNs were present in 50.0% of the 34 non-polypoid adenomas but only in 14.0% of the 50 polypoid adenomas.

CONCLUSIONS

Non-polypoid colonic adenomas evolve preferentially from the minimal fraction of the colonic mucosa that overlays the few existing lymphoid nodules in rats.

Different expressions of sialyl Tn antigen between polypoid and flat-type early colorectal cancers

PURPOSE

Sialyl Tn (STn) antigen is a cancer-associated carbohydrate antigen expressed in cancers of the digestive tract. We compared the proportion of specimens of flat-type colorectal cancers expressing STn with that of polypoid cancers, by examining the immunohistochemical reactivity of STn in various morphologic types of early and advanced colorectal cancers.

METHODS

A total of 111 biopsies from the colorectal area were examined for STn expression, including 11 adenomas, 58 early cancers, and 42 advanced cancers. Each section was stained immunohistochemically for STn antigen. In each section, we examined STn expression in the cancer area, adjacent mucosa, and normal epithelium.

RESULTS

STn expression was detected in 90.9 percent of adenomas, 36.2 percent of early cancers (T1), 64.3 percent of advanced cancers (>T1), and 52 percent of mucosa adjacent to cancer. The morphology of cancer tissue did not influence the number of specimens exhibiting STn antigen expression in mucosa adjacent to cancer cells. STn antigen was rarely expressed in flat or depressed-type early cancers (T1; 7.1 percent), and the expression was higher in moderately than in well-differentiated adenocarcinomas. In advanced cancers (>T1), a similar proportion of protruding and small ulcerative cancers expressed STn.

CONCLUSION

Our results suggest that the low expression of STn antigen in flat-type cancers may be the result of different mechanisms of cellular transformation during carcinogenesis from the usual adenoma-carcinoma sequence in colorectal neoplasms.

Induction of aberrant crypt foci and flat-type adenocarcinoma in the colons of dogs by N-ethyl-N'-nitro-nitrosoguanidine and their sequential changes

Sequential endoscopic observation of dog colons was performed during colon carcinogenesis. Two beagle dogs were given suppositories containing N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) every day for five months. In month 3, aberrant crypt foci (ACF), a putative preneoplastic lesion, were found in the colons of both dogs, but not in an untreated dog. The frequency of ACF increased until month 10, and then decreased. In month 9, very small lesions, less than 1 mm in diameter, which were similar to human early flat tumors, were first noticed. One of these lesions grew to about 7 mm in size without a change in its shape for 10 months. There were more than ten flat-type tumors in the two dogs, but such lesions were not found in the untreated dog. By biopsy, two of the lesions were proved to be well-differentiated adenocarcinomas histologically. Four polypoid lesions were found in one of the carcinogen-treated dogs. Thus, flat-type adenocarcinomas were induced in the dog colon by ENNG, and their development was followed by magnifying endoscopy.

Quantitative analysis of numerical chromosome aberrations in various morphological types of colorectal carcinomas

Quantitative analysis by fluorescence in situ hybridization (FISH) on thin paraffin-embedded tissue sections, using specific probes for chromosomes 11, 17, and 18 was employed in various morphological types of early and advanced colorectal cancer to clarify tumor cytogenetics. The chromosome index (CI) was calculated as a quantitative measure of the chromosome copy number. Compared with the CI of normal epithelium, the CI of chromosome 11 in villous components of adenomas or polypoid early cancers was decreased, while the CI in flat type or advanced colorectal cancers, conversely, was increased (P < 0.05). The CI of chromosome 17 in villous components of adenomas and all cancers was higher than that of normal epithelium (P < 0.05), but the differences were not significant. In protruding advanced cancers, the CI of chromosome 18 was significantly decreased (P < 0.01) compared to the CI of normal epithelium. There was no significant chromosomal heterogeneity between the superficial and the deepest layer in each cancer. In mucosa adjacent to sessile and flat type cancers, the CI of chromosome 17 was significantly higher than the CI in normal epithelium or adenomas (P < 0.05). These results suggest that numerical chromosome aberrations are associated with the histological type of adenoma and the morphological diversity of cancer in the colorectum, and that chromosome 17 abnormality occurs in mucosa adjacent to sessile and flat cancers.

Relationship between morphological diversity and AgNORs or cathepsin B expression in colorectal cancers

The biological characteristics associated with the morphological diversity of colorectal cancers were investigated to elucidate the causes of this diversity. We examined the proliferative and infiltrating activity of tumor cells, indicated by the mean number of Ag nucleolar organizer region associated proteins (NORs) per nucleus (MNA) and the immunohistochemical response to cathepsin B(CB), in various morphological types of early and advanced colorectal cancers. We examined 73 colorectal cancers obtained by endoscopic and surgical resection. MNA values for sessile and flat-elevated cancers were greater than the values for pedunculate, subpedunculate, and flat-or-depressed early cancers (sessile, P < 0.05). In advanced cancers invading the muscularis propria, protruding cancers showed significantly higher MNA values than small ulcerative cancers (P < 0.01). CB expression increased significantly with the progression of colorectal cancers (P < 0.01), but was not related to morphological diversity in early and advanced cancers. In both sessile and flat cancers, CB expression was higher in moderately differentiated than in well differentiated adenocarcinomas. These results indicate that, in colorectal cancers, protruding early cancers without stalks and protruding advanced cancers have higher proliferative activity than pedunculate or flat early cancers and small ulcerative advanced cancers, respectively, and that CB expression is not associated with morphological diversity, but with depth of invasion and histological differentiation.

Histologic classification of endoscopically removed flat colorectal polyps: a multicentric study

A total of 594 flat colorectal polyps, removed at endoscopy, were histologically classified into non-neoplastic (n = 49) and neoplastic (n = 545) polyps. Non-neoplastic polyps were subdivided into metaplastic (n = 45) and hyperplastic (n = 4), whereas neoplastic polyps were subdivided into adenomas (n = 481), intramucosal carcinomas (n = 28) and invasive adenocarcinomas (n = 36). Several adenoma phenotypes were discerned: tubular (n = 375), serrated (n = 59), villous (n = 39), mixed (n = 7) and fenestrated (n = 1). Intramucosal carcinomas were subdivided into tubular (n = 26) and serrated (n = 2), and invasive adenocarcinomas into tubular (n = 32), serrated (n = 3) and fenestrated (n = 1). The microscopic characteristics of each histologic phenotype described in this communication are defined and illustrated.

Flat adenoma as a precursor of colorectal carcinoma in hereditary nonpolyposis colorectal carcinoma

BACKGROUND

Because flat adenoma shows a higher malignancy rate compared with other types of polyps, it is considered to play an important role in the carcinogenesis of colorectal carcinoma. In the present study, we examined flat adenomas in hereditary nonpolyposis colorectal carcinoma (HNPCC) patients.

METHODS

Nine HNPCC patients who presented with flat adenomas were examined. All patients underwent either surgery or endoscopic polypectomy for colorectal carcinoma and/or adenoma. In all patients, annual colonoscopy had been performed once a year throughout the follow-up period after the initial treatment. When colorectal polyps were detected during follow-up colonoscopy, all lesions were endoscopically excised. Clinicopathologic features and microsatellite instability of both malignant lesions and adenomas were examined.

RESULTS

Thirteen malignant lesions were detected: seven advanced carcinomas and six early carcinomas. Among 4 early carcinomas with submucosal invasion, 3 lesions (75%) were categorized as superficial type, with a configuration similar to flat adenoma. The frequency of flat adenoma was strikingly high in HNPCC patients in the present study. Among 73 polyps detected, 37 (50.7%) were flat adenomas. Both malignant lesions and flat adenomas had proximal predominance, 61.5% and 59.5%, respectively. Eleven of 15 lesions (73.3%) showed replication error.

CONCLUSIONS

These results suggest the importance of flat adenoma as a precursor of colorectal carcinoma in some groups of HNPCC patients. Further study is essential to elucidate the natural history of flat adenomas in HNPCC patients.

Mutation of p53 tumor suppressor gene in flat neoplastic lesions of the colorectal mucosa

PURPOSE

In a recent comparative histologic survey of flat colorectal neoplasias, we found more lesions with high-grade dysplasia (HGD) and carcinoma in Japanese than in Swedish patients. The purpose of this work was to assess the p53 protein overexpression in flat colorectal neoplasias in Swedish patients and to compare results with those reported in Japan.

METHOD

A total of 57 neoplastic lesions of the colorectal mucosa were investigated: 29 had been regarded both at endoscopy and at histology as flat and the remaining 28 as exophytic. Deparaffinized, rehydrated sections were treated immunohistochemically to detect the p53 protein. Lesions having a moderate (++) or high ( ) staining were considered as overexpressing the p53 protein.

RESULTS

Results indicated that 16.7 percent (1/6) of the exophytic adenomas with low-grade dysplasia (LGD) had distinct p53 overexpression as well as 57.1 percent (8/14) of those with HGD and 87.5 percent (7/8) with invasive growth. In flat neoplastic lesions, 7.7 percent (1/13) of the tubular adenomas with LGD, 25 percent (3/12) of tubular adenomas with HGD, and 75 percent (3/4) of adenocarcinomas arising in flat adenomas had p53 overexpression.

CONCLUSIONS

In Swedish patients, the proportion of flat and exophytic colorectal neoplasias showing p53 immunoreactivity increased with increasing degree of dysplasia, the highest percent being recorded in lesions with invasive growth. Because a similar stepwise increase was reported for exophytic and flat colorectal neoplasias in Japan, it seems that the comparison of results in both countries is justifiable. One possible conclusion from this comparison is that the higher proportion of flat neoplastic colorectal lesions with HGD and carcinoma in the Japanese (compared with the Swedish) takes place for reasons extraneous to the overexpression of the p53 protein.

Flat adenomas and flat adenocarcinomas of the colorectal mucosa in Japanese and Swedish patients. Comparative histologic study

PURPOSE

In recent years, flat adenomas of the colorectal mucosa have been intensively investigated by Japanese pathologists. Results of that work indicate that flat adenomas may antedate the development of colorectal carcinomas. Because of differences in the histologic definition of flat adenomas with severe dysplasia and with intramucosal carcinoma within the group, one single observer having both Western and Asian training in pathology reviewed the material.

METHODS

A total of 287 flat colorectal lesions were reviewed: 109 from the Karolinska Hospital, Stockholm, 137 from the Tokyo Medical and Dental University (TMDU) (which included 5 cases from the Nagoya City University), and 41 from the Cancer Institute (CI), Tokyo. Lesions were histologically classified following strict histologic criteria. Thus, flat adenomas were divided into those having low-grade dysplasia (LGD; having dysplastic cells in the deeper half of the epithelium), high-grade dysplasia (HGD; dysplastic cells were found even in the superficial half of the epithelium), intramucosal carcinoma (dysplastic glands displayed molding with buddings and often a cribriform pattern), and adenocarcinoma (braking through the muscularis mucosa, with neoplastic cells in the submucosal layer or deeper).

RESULTS

Whereas in Stockholm only 14.7 percent of lesions had HGD, as much as 56.9 percent and 56.1 percent, respectively, had HGD at the two Tokyo Hospitals. Intramucosal carcinomas were not found in the Stockholm material but occurred in 2.2 percent of lesions seen at TMDU and in 4.9 percent of those seen at the CI. Notably, only 2.7 percent of the specimens at Karolinska Hospital had invasive adenocarcinoma, but it was seen in as many as 4.4 percent at TMDU and 21.9 percent at the CI.

CONCLUSIONS

This study indicates that there were histologic differences between flat neoplasias of the colorectal mucosa harvested in Stockholm and Tokyo. In Japan lesions were obviously more advanced (in terms of HGD) and more aggressive (in terms of intramucosal and submucosal invasion). The cause for the differences found in those two disparate geographic regions remains poorly understood. The results, however, may help us understand some of the unclear points and discussions appearing in the literature on this subject.

p53 overexpression in flat serrated adenomas and flat tubular adenomas of the colorectal mucosa

The expression of the p53 protein was investigated in flat serrated neoplasias as well as in other histological phenotypes of flat or exophytic hyperplasias or neoplasias of the colorectal mucosa. A total of 104 such lesions were analyzed: 24 were flat serrated neoplasias (22 flat serrated adenomas and 2 flat serrated adenocarcinomas), 26 flat tubular adenomas, 17 flat hyperplastic polyps, 29 exophytic tubular and/or villous neoplasias (23 adenomas and 6 exophytic adenocarcinomas) and the remaining 8, exophytic hyperplastic polyps. Deparaffinized, rehydrated sections were treated immunohistochemically to detect those overexpressing the p53 protein. Lesions having slight (+), moderate (++) or intense ( ) staining were considered immunoreactive. The results showed that 50% of the flat serrated adenomas with low-grade dysplasia (LGD) and 66.7% of those with high-grade dysplasia (HGD) had p53 immunoreactivity. None of the flat tubular or of the exophytic adenomas with LGD expressed p53, but immunoreactivity was present in 61.5% of the flat tubular adenomas with HGD and in 52.3% of the exophytic adenomas with HGD. All adenocarcinomas had an intense p53 reaction. Weak p53 expression was demonstrated by 11.7% of the flat hyperplastic polyps but none of the exophytic polyps reacted. The occurrence of p53 expression in flat serrated adenomas with LGD suggested that, despite its low histological profile, one-half of those lesions could be biologically already committed to independent growth. The occurrence of p53 expression in nearly 12% of the flat hyperplastic polyps was totally unexpected and deserves further investigation. Flat serrated adenoma emerges as a novel, independent histological entity among the various phenotypes of flat neoplasias of the colorectal mucosa.