Bidirectional gastric differentiation in cellular mucin phenotype (foveolar and pyloric) in serrated adenoma and hyperplastic polyp of the colorectum

Ki-67 distribution, α-methylacyl-CoA racemase (AMACR) expression and mucin phenotypes are associated with non-polypoid growth in ulcerative colitis-associated neoplasia

AIMS

Ulcerative colitis-associated neoplasia (UCAN) is characterised by multifocal tumourigenesis. A wide range of metachronous lesions have been reported to occur after endoscopic treatment of UCAN, which suggests the development of sporadic tumours in lesions treated as UCAN. Therefore, we aimed to evaluate differences of immunohistochemistry (IHC) in features and clinicopathological characteristics of intramucosal lesions in patients with ulcerative colitis (UC).

METHODS AND RESULTS

We examined 35 intramucosal lesions resected for carcinoma or dysplasia by total colectomy from patients with UC and 71 sporadic adenomas (SAs) endoscopically resected from patients without UC. UC lesions were divided into the conventional UCAN group, defined as p53 mutant pattern and normal expression of β-catenin, and the non-conventional UCAN group, defined as the rest. Ki-67 distribution, α-methylacyl-CoA racemase (AMACR) expression and mucin phenotypes were compared using IHC, and clinicopathological characteristics were investigated. Conventional and non-conventional UCAN lesions were located in the left colon and rectum. Relative to the SA lesions, UCAN lesions occurred in much younger patients and exhibited more frequent basal distribution of Ki-67 in tumour crypts. Conventional UCAN lesions tended to be non-polyploid and exhibited a higher frequency of normal AMACR expression than SA lesions. UC lesions were heterogeneous-only two of the eight patients with multiple lesions had lesions (both non-conventional UCAN lesions) exhibiting concordant IHC staining features.

CONCLUSIONS

The basal pattern of Ki-67 distribution, normal expression of AMACR and a non-intestinal mucin phenotype were determined as characteristic features suggestive of UCAN. Non-polypoid growth was another a key feature of UCAN.

[Comparative assessment of the expression of Muc 2, Muc 5AC, and Muc 6 in serrated neoplasms of the colon]

In the course of the serrated pathway of carcinogenesis, there are changes in the expression of mucins with a characteristic immunophenotypic sign, such as a late loss of intestinal differentiation and an increase in gastric differentiation.

OBJECTIVE

To comparatively assess the expression of Muc 2, Muc 5AC, and Muc 6 in hyperplastic polyps (HPs), sessile serrated adenomas (SSAs) and traditional serrated adenomas (TSAs) of the colon for determination of their role in differential diagnosis.

MATERIAL AND METHODS

Sixty-five serrated masses from 52 patients were examined. Among them, there were 26 SSAs, 26 HPs, and 13 TSAs. A histological examination was done using hematoxylin and eosin staining; periodic acid-Schiff reaction in combination with alcian blue, as well as immunohistochemistry with anti-Muc 2, anti-Muc 5AC, and anti-Muc 6 antibodies were used. Genetic testing of the specimens for KRAS and BRAF mutations was also carried out.

RESULTS

All the serrated neoplasms of the colon exhibited a pronounced expression of Muc 2. A marked Muc 6 expression in the dilated crypt bases was found in 76.9% of SSAs, while no reaction was seen in 92.3% of HPs and in 100% of TSAs. SSAs were characterized by an intense Muc 5AC expression in the whole length of the crypts and in the surface epithelium in contrast with HPs and TSAs, where the expression of the marker was focal. Comparison of the response of the markers and the presence of gene mutations identified that the SSAs with BRAF mutation intensely expressed along the length of the crypt for Muc 5AC and Muc 6; and the TSAs with KRAS mutation had a moderate focal Muc 5AC expression in the crypt bases in 100% of cases.

CONCLUSION

For differential diagnosis of the types of serrated adenomas of the colon, it is useful for a pathologist to apply the immunohistochemical markers Muc 2, Muc 5AC, and Muc 6 in his/her practice.

Ectopic Gastric and Intestinal Phenotypes, Neuroendocrine Cell Differentiation, and SOX2 Expression Correlated With Early Tumor Progression in Colorectal Laterally Spreading Tumors

INTRODUCTION

The significance of the ectopic gastric phenotype remains unclear in patients with colorectal laterally spreading tumors (LSTs). We investigated clinicopathologic differences among LST subtypes, aiming to identify factors indicative of malignant transformation and invasion that are linked to ectopic gastric phenotype and tumor progression.

MATERIALS AND METHODS

We analyzed the morphologic characteristics of 105 colorectal LSTs resected by endoscopic submucosal dissection. LSTs were classified into 2 subtypes: granular (G-LST) and nongranular (NG-LST). Resected LSTs were analyzed histologically and were immunohistochemically stained for MUC5AC, MUC6, chromogranin A, CD10, and SOX2.

RESULTS

The 105 LSTs included 60 G-LSTs and 45 NG-LSTs. By histology, G-LSTs comprised 5 adenomas with low-grade dysplasia (LAs), 45 adenomas with high-grade dysplasia (HAs), and 10 adenocarcinomas invading the submucosa (SMs). NG-LSTs comprised 8 LAs, 25 HAs, and 12 SMs. MUC5AC positivity was significantly higher in G-LSTs compared to NG-LSTs (P = .002), and MUC5AC positivity in HA lesions was significantly higher than in LA lesions (P = .01). MUC6 and SOX2 positivity in SM G-LSTs, and chromogranin A positivity in SM NG-LSTs were significantly higher than in HAs (P = .01, .01, and .03, respectively). CD10 positivity in SM NG-LSTs was significantly higher than in HAs and LAs (P = .02 and .01, respectively).

CONCLUSION

Ectopic gastric and intestinal phenotypes, neuroendocrine cell differentiation, and SOX2 expression differ according to tumor grade in colorectal LSTs, and these markers are correlated with early tumor progression in each LST subtype.

Pathological features of the sessile serrated adenoma/polyp with special references of its carcinogenesis

The sessile serrated adenoma/polyp (SSA/P) has been thought as the relatively new precursor for the colorectal cancer. In the current review, the well-known pathological features including the histological definition of the SSA/P are described using the previous reports. Although the SSA/P is thought one of pre-cancerous lesions of the colorectal carcinoma, the decisive or documentary lesion like "carcinoma in adenoma" is very rare. In this review, the strict case of the carcinoma derived from the SSA/P is demonstrated using our cases. Although the genetic investigations of the SSA/P have shown the new pathway of colorectal carcinogenesis and these concepts are thought to be almost right, the verification for them should be performed using "the carcinoma in SSA/P" like the present case.

Serrated polyps of the colon: how reproducible is their classification?

For several years, the lack of consensus on definition, nomenclature, natural history, and biology of serrated polyps (SPs) of the colon has created considerable confusion among pathologists. According to the latest WHO classification, the family of SPs comprises hyperplastic polyps (HPs), sessile serrated adenomas/polyps (SSA/Ps), and traditional serrated adenomas (TSAs). The term SSA/P with dysplasia has replaced the category of mixed hyperplastic/adenomatous polyps (MPs). The present study aimed to evaluate the reproducibility of the diagnosis of SPs based on currently available diagnostic criteria and interactive consensus development. In an initial round, H&E slides of 70 cases of SPs were circulated among participating pathologists across Europe. This round was followed by a consensus discussion on diagnostic criteria. A second round was performed on the same 70 cases using the revised criteria and definitions according to the recent WHO classification. Data were evaluated for inter-observer agreement using Kappa statistics. In the initial round, for the total of 70 cases, a fair overall kappa value of 0.318 was reached, while in the second round overall kappa value improved to moderate (kappa = 0.557; p < 0.001). Overall kappa values for each diagnostic category also significantly improved in the final round, reaching 0.977 for HP, 0.912 for SSA/P, and 0.845 for TSA (p < 0.001). The diagnostic reproducibility of SPs improves when strictly defined, standardized diagnostic criteria adopted by consensus are applied.

Mucin phenotype and narrow-band imaging with magnifying endoscopy for differentiated-type mucosal gastric cancer

BACKGROUND

Several studies have described the surface glandular structure in differentiated early gastric cancer observed by narrow-band imaging with magnifying endoscopy (NBI-ME) in two main patterns, i.e., a papillary or granular structure in an intralobular loop pattern (ILL) and a pit structure in a fine network pattern (FNP). However, it is uncertain why the NBI-ME findings of differentiated-type carcinomas are divided into two main patterns. We investigated the significance of the mucin phenotype in the morphogenetic difference between ILL and FNP.

METHODS

We evaluated 120 intramucosal, well- or predominantly well-differentiated tubular adenocarcinomas. In each lesion, one area that showed the predominant pattern of microsurface structures and microvessels was selected and marked by electrocoagulation for a strict comparative study by NBI-ME and pathological investigation. NBI-ME findings were classified into three patterns: ILL, FNP, and intermediate. Mucin phenotypes were judged as gastric, intestinal, or gastrointestinal type by immunohistochemistry.

RESULTS

The mucin phenotype was gastric or gastrointestinal type in 24 (92.3%) of 26 ILL lesions. Intestinal phenotype was observed in 22 (84.6%) of 26 FNP lesions. The gastrointestinal phenotype was observed in 50 (73.5%) of 68 intermediate pattern lesions. The mucin phenotype and NBI-ME results were significantly correlated (P < 0.001).

CONCLUSIONS

The mucin phenotype of differentiated early gastric cancer might be involved in morphogenetic differences between the papillary and pit structures visualized by NBI-ME.

Hyperplastic polyp of the duodenum: a report of 9 cases with immunohistochemical and molecular findings

Benign serrated polyps are commonly found in the colorectum but have rarely been described in other parts of the gastrointestinal tract. We report a series of 9 serrated polyps arising in the duodenum with clinicopathologic features, immunohistochemical expression profile of mucins (MUC2, MUC5AC, MUC6), and molecular analysis for BRAF and KRAS. The polyps were diagnosed as incidental endoscopy findings in 9 different patients, comprising 3 male and 6 female patients, with a mean age of 52.2 years (range, 21-72 years). The second part of the duodenum was the most common site (n = 5), followed by the ampulla (n = 1) and the distal duodenum (n = 1), with the location of the 2 remaining polyps unspecified. Other upper gastrointestinal tract pathology features included Barrett esophagus for 5 patients, Helicobacter gastritis for 1 patient, and mild chronic gastritis for 1 patient. The histologic appearance of the polyps was similar to microvesicular hyperplastic polyp in the colorectum. Immunostaining for mucins showed MUC6 expression in the crypt bases of all polyps, MUC5AC expression in 8 cases (89%), and mucin 2 expression in 6 cases (67%). Molecular testing was successful in 6 polyps, showing BRAF mutation (V600E) in 2 polyps, KRAS mutation in 2 polyps, and no mutation for either gene in 2 polyps. Colonoscopy reports were available for 6 patients, of whom 4 were diagnosed with hyperplastic polyps or sessile serrated polyps in the colorectum. However, no patient met the criteria for serrated polyposis. Although probably rare and of uncertain malignant potential, hyperplastic polyp should be considered in the differential diagnosis of benign duodenal polyp.

Filiform serrated adenomatous polyposis arising in a diverted rectum of an inflammatory bowel disease patient

A 54-year-old man, previously colectomized for inflammatory bowel disease, developed carcinoma in the inflamed rectum stump. The malignant growth was surrounded by a filiform polyposis, grossly considered as pseudopolyps. The histology disclosed, however, a morphology corresponding to the recently described filiform subset of serrated adenoma (FSA). The clustering of the FSA amounted to a filiform serrated adenomatous polyposis, a hitherto unreported observation. It is speculated that neoplastic transformation of pre-existing pseudopolyps and prolaps-related events lead to this peculiar morphology. Minor zones with a villous structure were admixed as were small areas of traditional serrated adenoma and patches of flat dysplasia. Although a combined gastric and intestinal (positivity for MUC5AC, MUC2, MUC6, CDX2) immunoprofile characterized the adenomatous component, a downregulation of the gastric mucin along with a loss of the serrated attribute accompanied the malignant transformation. An added dynamic shift during the adenoma carcinoma sequence included the acquisition of CK7 expression in the malignant portion. Gastric mucin may play a role in the initial step of the neoplastic evolution and CK7 may denote neoplastic progression. This case confirms the notion of a widely variegated morphology of precursor lesions of colorectal carcinoma arising in a chronically inflamed bowel as opposed to the generally more monotonous appearance of adenomas in a sporadic context.

Serrated lesions of the appendix: a morphologic and immunohistochemical appraisal

We performed a histologic and immunohistochemical assessment of 53 noninvasive appendiceal epithelial proliferations, appropriating terminology and using markers shown useful in differentiating serrated colorectal polyps. These were classified as hyperplastic polyp (HP), sessile serrated adenoma (SSA), mixed serrated and adenomatous lesion (MSAL), mucinous cystadenoma (MCA), or conventional adenoma (CAD). Immunohistochemical analysis for cytokeratin (CK) 20, Ki-67, MUC6, and beta-catenin was performed. Diagnoses were as follows: HP, 6; SSA, 12; HP vs SSA, 3; MSAL, 16; MCA, 14; and CAD, 2. All HPs showed expanded (beyond surface) CK20 and expanded or normal (base) Ki-67; 1 was MUC6+. Most SSAs and MSALs were CK20-expanded or expanded with random expression in deep crypts (Ex/I) and Ki-67-expanded, Ex/I (expanded with asymmetry), or normal. All SSAs and 8 of 16 MSALs were MUC6+. CADs were CK20-Ex/I, Ki-67-Ex, and MUC6-; 1 showed nuclear beta-catenin expression. Serrated appendiceal lesions can be categorized using colorectal terminology. MUC6 is associated with SSA morphologic features. Similar immunohistochemical patterns in SSA and MSAL suggest a link between these lesions.

Expression of gastric pyloric mucin, MUC6, in colorectal serrated polyps

Serrated polyps of the colorectal mucosa represent a heterogeneous and controversial taxonomic category with variation in histopathological, molecular, and immunohistochemical characteristics and with an incomplete understanding of pathogenesis. A previous study reported that the expression of gastric pyloric-type mucin, MUC6, characterized sessile serrated adenomas. We therefore evaluated the expression of MUC6 in serrated polyps identified among 2502 participants in a Phase III chemoprevention trial within the Arizona Cancer Center Colorectal Cancer Prevention Trials Program and characterized the associated histopathological features and location. We carried out immunohistochemistry for MUC6 on 146 serrated lesions and 87 conventional tubular adenomas, and assessed the percentage of cells with expression and the grade of staining intensity. In all 92 hyperplastic polyps, 43 sessile serrated adenomas, and 11 traditional serrated adenomas were included. Polyps ranged in size from 1-150 mm. The association of MUC6 staining with serrated polyp category was evaluated using classification and regression tree (CART) analysis and two-sided Fisher's exact test. A total of 53% of sessile serrated adenomas (n=23), 17% of hyperplastic polyps (n=16), and 18% of traditional serrated adenomas (n=2), but none of 87 tubular adenomas, expressed MUC6. Expression was limited to the lower crypts in all serrated polyps. The extent of positive staining ranged from 2-100% of crypt cells and was independent of the histopathological type. MUC6 expression had relatively high specificity for sessile serrated adenoma (82%) but low sensitivity (54%). In CART analysis, proximal location was found to be the best partitioning factor for MUC6, followed by classification as sessile serrated adenoma. We conclude that MUC6 expression is strongly associated with proximal location of serrated polyps, but only has modest utility as a tissue biomarker for sessile serrated adenoma.

Superficially elevated-type serrated hyperplastic lesion of the stomach with minute adenocarcinoma

We report a case of gastric serrated hyperplastic lesion with minute adenocarcinoma. A 65-year-old Japanese man underwent endoscopic submucosal dissection to the superficially elevated-type (0-IIa) lesion located at the lesser curvature of the gastric angle. Histological observation revealed hyperplastic change of foveolar epithelium with serrated glandular structure as well as a minute tubular adenocarcinoma component. Immunohistochemically, the lesion demonstrated gastrointestinal, predominantly gastric, phenotype (MUC5AC++, MUC6+, MUC2+, CD10-). Positive p53 immunoreactivity was detected in the carcinoma component of the lesion with a point mutation (G877T; R209I) of the gene and microsatellite instability of the BAT-RII locus; however, immunoreactivity of the mismatch repair gene product hMLH1 was well preserved in the cancer as well as in the hyperplastic lesion. The hyperplastic lesion with serrated glandular pattern would be a precancerous lesion of adenocarcinoma of the stomach.

Selective expression of gastric mucin MUC6 in colonic sessile serrated adenoma but not in hyperplastic polyp aids in morphological diagnosis of serrated polyps

Colonic sessile serrated adenoma, in contrast to hyperplastic polyp, is thought to be related to sporadic colorectal cancers with high microsatellite instability. However, the morphological distinction between these entities is difficult and subject to observer and sampling variation. Therefore, we elected to investigate the expression of gastric mucin MUC6 as a potential marker to separate the two in the hope of finding an objective and reproducible adjunct to morphological diagnosis. Endoscopic biopsies of colonic polyps with serrated architecture, but without cytological dysplasia were studied and categorized as sessile serrated adenoma or hyperplastic polyp, using previously published morphological criteria. Smaller groups of serrated polyps with cytological dysplasia (traditional serrated adenomas, filiform serrated adenomas and sessile serrated adenomas with cytological dysplasia) were also included. In total, 94 polyps were immunohistochemically stained with antibodies to MUC6 and to MLH-1. MUC6 was found to have 100% specificity in distinguishing sessile serrated adenoma (N=26; positive staining) from hyperplastic polyp (N=48; negative staining). Traditional serrated adenomas and filiform serrated adenomas were also negative for MUC6. Sessile serrated adenomas with cytological dysplasia were found to lose expression of MLH-1 in dysplastic areas, while retaining MUC6 expression. Neither anatomic location in the right or left colon nor polyp size appears to account for the differences in MUC6 expression.

Hyperplastic polyps and sessile serrated 'adenomas' of the colon and rectum display gastric pyloric differentiation

The serrated polyp-neoplasia pathway is a novel concept that has been demonstrated to differ from the conventional adenoma-carcinoma pathway. To characterize the phenotypic patterns of differentiation in colorectal serrated polyps, we examined the immunohistochemical expression profile of gastric (MUC5AC, TFF1, MUC6, GlcNAcalpha1 --> 4Gal --> R, and PDX1) and intestinal (MUC2, TFF3, and CDX2) epithelial markers in 15 hyperplastic polyps (HPs), 29 sessile serrated adenomas (SSAs),12 traditional serrated adenomas (TSAs), and 16 conventional adenomas (CAs). MUC5AC and TFF1 were upregulated in the HPs, SSAs, and TSAs. MUC6 was expressed in the HPs and SSAs. GlcNAcalpha1 --> 4Gal --> R was expressed only in the SSAs. Although MUC2 expression was preserved, TFF3 was downregulated in the HPs, SSAs, and TSAs. PDX1 was upregulated in the HPs, SSAs, and TSAs. On the other hand, CDX2 was downregulated in the HPs and SSAs. The colorectal serrated polyps showed higher expression of gastric makers than CAs. The HPs and SSAs showed gastric and intestinal mixed phenotype expression with gastric pyloric organoid differentiation and almost identical, but different from the TSAs, marker profile. PDX1 up-regulation and CDX2 down-regulation could be important for the induction of a gastric pyloric pattern of cell differentiation in colorectal serrated polyps.