Beta-catenin mutations in sporadic fundic gland polyps

Decoding the basis of histological variation in human cancer

Molecular abnormalities that shape human neoplasms dissociate their phenotypic landscape from that of the healthy counterpart. Through the lens of a microscope, tumour pathology optically captures such aberrations projected onto a tissue slide and has categorized human epithelial neoplasms into distinct histological subtypes based on the diverse morphogenetic and molecular programmes that they manifest. Tumour histology often reflects tumour aggressiveness, patient prognosis and therapeutic vulnerability, and thus has been used as a de facto diagnostic tool and for making clinical decisions. However, it remains elusive how the diverse histological subtypes arise and translate into pleiotropic biological phenotypes. Molecular analysis of clinical tumour tissues and their culture, including patient-derived organoids, and add-back genetic reconstruction of tumorigenic pathways using gene engineering in culture models and rodents further elucidated molecular mechanisms that underlie morphological variations. Such mechanisms include genetic mutations and epigenetic alterations in cellular identity codes that erode hard-wired morphological programmes and histologically digress tumours from the native tissues. Interestingly, tumours acquire the ability to grow independently of the niche-driven stem cell ecosystem along with these morphological alterations, providing a biological rationale for histological diversification during tumorigenesis. This Review comprehensively summarizes our current understanding of such plasticity in the histological and lineage commitment fostered cooperatively by molecular alterations and the tumour environment, and describes basic and clinical implications for future cancer therapy.

Region-specific Wnt signaling responses promote gastric polyp formation in patients with familial adenomatous polyposis

Germline adenomatous polyposis coli (APC) mutation in patients with familial adenomatous polyposis (FAP) promotes gastrointestinal polyposis, including the formation of frequent gastric fundic gland polyps (FGPs). In this study, we investigated how dysregulated Wnt signaling promotes FGPs and why they localize to the corpus region of the stomach. We developed a biobank of FGP and surrounding nonpolyp corpus biopsies and organoids from patients with FAP for comparative studies. Polyp biopsies and polyp-derived organoids exhibited enhanced Wnt target gene expression. Polyp-derived organoids with intrinsically upregulated Wnt signaling showed poor tolerance to further induction, suggesting that high Wnt restricts growth. Targeted genomic sequencing revealed that most gastric polyps did not arise via APC loss of heterozygosity. Studies in genetic mouse models demonstrated that heterozygous Apc loss increased epithelial cell proliferation in the corpus but not the antrum, while homozygous Apc loss was not maintained in the corpus yet induced hyperproliferation in the antrum. Our findings suggest that heterozygous APC mutation in patients with FAP may be sufficient to drive polyp formation in the corpus region while subsequent loss of heterozygosity to further enhance Wnt signaling is not tolerated. This finding contextualizes the abundant yet benign nature of gastric polyps in FAP patient corpus compared with the rare, yet adenomatous polyps in the antrum.

Fundic Gland Polyps Lack DNA Content Abnormality Characteristic of Other Adenomatous Precursor Lesions in the Gastrointestinal Tract

Fundic gland polyps (FGPs) develop sporadically (frequently after proton pump inhibitor therapy) or in the setting of a hereditary polyposis syndrome, such as familial adenomatous polyposis (FAP). FAP-related FGPs often demonstrate low-grade dysplasia (LGD) and are frequently associated with APC mutations, even in the absence of dysplasia. Sporadic FGPs with dysplasia are molecularly similar to FAP-related FGPs and demonstrate frequent mutations in APC gene. Despite having similar molecular alterations with colorectal and other adenomatous precursor lesions in the gastrointestinal (GI) tract, FGPs rarely progress to advanced gastric neoplasia (high-grade dysplasia [HGD] or adenocarcinoma), and their role in gastric tumorigenesis remains unclear but likely limited. The clinicopathologic features of 192 patients diagnosed with FGPs, including 86 with FAP-related FGPs (33 with dysplastic FGPs and 53 with nondysplastic FGPs) and 106 with sporadic FGPs (12 with dysplastic FGPs and 94 with nondysplastic FGPs), were analyzed. DNA flow cytometry was performed on 111 FAP-related FGP biopsies, including 32 FGPs with LGD and 79 nondysplastic FGPs, to assess the presence of abnormal DNA content (ie, aneuploidy or elevated 4N fraction). Moreover, 40 sporadic FGP biopsies, including 14 dysplastic (13 LGD and 1 HGD) and 26 nondysplastic FGPs, were examined for DNA content abnormality. Patients with FAP and nondysplastic FGPs were more likely to be younger (mean age, 32 years) and present with multiple FGPs (92%, defined as having ≥2 FGPs) than those with sporadic nondysplastic FGPs (61 years and 65%, respectively; P < .001). They also recorded higher rates of previous or concurrent gastric epithelial dysplasia not occurring in a FGP (8%, P = .016), nongastric GI dysplasia (96%, P < .001), and nongastric GI malignancy (17%, P = .001) compared with those with sporadic nondysplastic FGPs (0%, 52%, and 2%, respectively). The sporadic group was more frequently associated with proton pump inhibitor therapy (78%, P < .001), gastric intestinal metaplasia (24%, P = .004), and a family history of gastric cancer (10%, P = .027) than the FAP group (19%, 6%, and 0%, respectively). Almost all FAP-related FGPs had a polypoid endoscopic appearance (98% vs 84% for sporadic FGPs; P = .009). The mean size of the largest FAP-related FGPs (0.5 cm) was similar to that of sporadic FGPs (0.7 cm) (P = .069). None of the 147 patients with FAP-related or sporadic nondysplastic FGPs were associated with subsequent detection of advanced gastric neoplasia within a mean follow-up time of 54 months (range, <1 to 277 months). However, 2 (4%) of the 45 patients with FAP-related or sporadic dysplastic FGPs developed advanced gastric neoplasia within a mean follow-up time of 59 months (range, <1 to 236 months). One (3%) of the 33 patients with FAP and dysplastic FGPs developed signet ring cell adenocarcinoma, whereas 1 (8%) of the 12 patients with sporadic dysplastic FGPs developed HGD (P = .445). However, none of the FAP-related and sporadic FGP biopsies, regardless of the presence or absence of dysplasia, demonstrated DNA content abnormality. In conclusion, FGPs lack large-scale chromosomal changes that are characteristic of the typical adenoma-carcinoma sequence involved in the development of other GI malignancies. Progression to advanced gastric neoplasia is rare in FGPs, which may be partly explained by the apparent lack of the chromosomal instability phenotype in these lesions.

Transcriptome analysis reveals the essential role of NK2 homeobox 1/thyroid transcription factor 1 (NKX2-1/TTF-1) in gastric adenocarcinoma of fundic-gland type

BACKGROUND

Gastric adenocarcinoma of fundic-gland type (GA-FG) is a gastric malignancy with little relation to Helicobacter pylori. Clinical characteristics of GA-FG have been established, but molecular mechanisms leading to tumorigenesis have not yet been elucidated.

METHODS

We subjected three GA-FG tumors-normal mucosa pairs to microarray analysis. Network analysis was performed for the top 30 up-regulated gene transcripts, followed by immunohistochemical staining to confirm the gene expression analysis results. AGS and NUGC4 cells were transfected with the gene-encoding NK2 homeobox 1/thyroid transcription factor 1 (NKX2-1/TTF-1) to evaluate transcriptional changes in its target genes.

RESULTS

Comprehensive gene expression analysis identified 1410 up-regulated and 1395 down-regulated gene probes with ≥ two-fold difference in expression. Among the top 30 up-regulated genes in GA-FG, we identified transcription factor NKX2-1/TTF-1, a master regulator of lung/thyroid differentiation, together with surfactant protein B (SFTPB), SFTPC, and secretoglobin family 3A member 2(SCGB3A2), which are regulated by NKX2-1/TTF-1. Immunohistochemical analysis of 16 GA-FG specimens demonstrated significantly higher NKX2-1/TTF-1 and SFTPB levels, as compared to that in adjacent normal mucosa (P < 0.05), while SCGB3A2 levels did not differ (P = 0.341). Transduction of NKX2-1/TTF-1 into AGS and NUGC4 cells induced transactivation of SFTPB and SFTPC, indicating that NKX2-1/TTF-1 can function as normally in gastric cells as it can in the lung cells.

CONCLUSIONS

Our first transcriptome analysis of GA-FG indicates significant expression of NKX2-1/TTF1 in GA-FG. Immunohistochemistry and cell biology show ectopic expression and normal transactivation ability of NKX2-1/TTF-1, suggesting that it plays an essential role in GA-FG development.

Long term outcomes of sporadic large fundic gland polyps: a single-center experience

BACKGROUND AND STUDY AIMS

Sporadic fundic gland polyps (FGP) are the most common type of gastric polyp, reported in 0.8%-1.9% of patients undergoing Esophagogastroduodenoscopy (EGD). Data on long-term outcomes of large FGP is limited. We aim to study the natural history of sporadic large (≥ 10 mm) FGPs.

PATIENTS AND METHODS

All adults who underwent EGD for any indication from April 2014 to December 2019 at a tertiary care center were retrospectively assessed, and patients with FGP (≥10mm) were identified. Data on baseline characteristics and long-term outcomes were recorded. Follow-up data were recorded for patients who underwent repeat endoscopy to evaluate for rates of dysplasia and cancer.

RESULTS

A total of 4,000 patients with a diagnosis of FGP were screened and 132 large, biopsy-proven FGPs were included in the final analysis. The most common indication for EGD was gastroesophageal reflux disease (61%). During a follow-up period of 3.2 years, the rate of dysplasia, was 4.0%. Subgroup analysis based on size (10-19 mm and ≥ 20 mm) showed no significant difference in overall outcomes.

CONCLUSION

Repeat EGDs for surveillance should not be routinely performed since large (≥10 mm) sporadic FGPs are mostly benign without significant malignant potential.

Molecular Alterations in Gastric Preneoplastic Lesions and Early Gastric Cancer

Prognosis of gastric cancer is dramatically improved by early diagnosis. Correa's cascade correlates the expression of some molecular markers with the progression of preneoplastic lesions toward carcinoma. This article reviews the diagnostic and prognostic values of molecular markers in complete (MUC2) and incomplete (MUC2, MUC5AC, and MUC6) intestinal metaplasia, gastric dysplasia/intra-epithelial neoplasia, and early gastric cancer. In particular, considering preinvasive neoplasia and early gastric cancer, some studies have demonstrated a correlation between molecular alterations and prognosis, for example, mucins phenotype in gastric dysplasia, and GATA6, TP53 mutation/LOH and MUC6 in early gastric cancer. Moreover, this review considers novelties from the literature regarding the (immuno)histochemical characterization of diffuse-type/signet ring cell gastric cancer, with particular attention to clinical outcomes of patients. The aim of this review is the evaluation of the state of the art regarding suitable biomarkers used in the pre-surgical phase, which can distinguish patients with different prognoses and help decide the best therapeutic strategy.

Gastritis, Gastric Polyps and Gastric Cancer

Gastric cancer is still an important disease causing many deaths worldwide, although there has been a marked reduction in prevalence during the last few decades. The decline in gastric cancer prevalence is due to a reduction in Helicobacter pylori infection which has occurred for at least 50 years. The most probable mechanism for the carcinogenic effect of H. pylori is hypergastrinemia since H. pylori infected individuals do not have increased risk of gastric cancer before the development of oxyntic atrophy. When atrophy has developed, the carcinogenic process continues independent of H. pylori. Autoimmune gastritis also induces oxyntic atrophy leading to marked hypergastrinemia and development of ECL cell neoplasia as well as adenocarcinoma. Similarly, long-term treatment with efficient inhibitors of acid secretion like the proton pump inhibitors (PPIs) predisposes to ECL cell neoplasia of a different degree of malignancy. Contrasting the colon where most cancers develop from polyps, most polyps in the stomach have a low malignant potential. Nevertheless, gastric polyps may also give rise to cancer and have some risk factors and mechanisms in common with gastric cancer. In this overview the most common gastric polyps, i.e., hyperplastic polyps, adenomatous polyps and fundic gland polyps will be discussed with respect to etiology and particularly use of PPIs and relation to gastric carcinogenesis.

Sporadic foveolar-type gastric adenoma with a raspberry-like appearance in Helicobacter pylori-naïve patients

Sporadic foveolar-type gastric adenoma (FGA) has been described as an extremely rare polyp that is whitish and flatly elevated. However, we recently found that sporadic FGA with a raspberry-like appearance (FGA-RA) is not rare in Helicobacter pylori (H. pylori)-naïve gastric mucosa. We endoscopically or surgically treated 647 patients with gastric epithelial neoplasms in the last 5 years, with 7.7% (50/647) being H. pylori-naïve. Among these, 43 FGA-RAs were diagnosed based on histologic and endoscopic features in 34 patients, who were all enrolled in this retrospective study. All lesions were observed by white-light endoscopy (WLE) and narrow-band imaging with magnification endoscopy (NBIME). We subsequently analyzed their endoscopic and microscopic features and patient characteristics. The patients were 22 males and 12 females aged 57±23 years (mean±2SD). WLE showed raspberry-like small polyps mimicking gastric hyperplastic polyps in the oxyntic gastric compartment (body/fundus). Multiple growths were confirmed in 20.6% (7/34) of the patients. NBIME revealed irregularly shaped papillary/gyrus-like microstructures with abnormal capillaries. Histologically, all lesions were intraepithelial neoplasms, and most of lesions (62.8%, 27/43) exhibited low-grade dysplasia. Immunohistochemically, neoplastic cells featured strong and diffuse MUC5AC expression, negative or very low MUC6 expression, and negative MUC2/CD10 expression. They also showed Ki-67 hyperexpression with a mean labeling index of 59.4±48.7%. The coexistence of fundic gland polyps in the background mucosa was significantly higher in multiple FGA-RA cases than in solitary cases (100% vs. 55.5%, P< 0.05). FGA-RA is a newly suggested histologic variant of sporadic FGA whose occurrence is not rare in daily endoscopic practice.

Sporadic pyloric gland adenoma associated with a large fundic gland polyp: genetic evidence for stepwise progression

Pyloric gland adenoma (PGA) is an uncommon variant of gastric adenoma exhibiting pyloric gland/mucous neck cell differentiation. We present a sporadic PGA associated with a large fundic gland polyp (FGP) in a woman in her 40 s without Helicobacter pylori infection. The polyp, measuring 25 mm in size, was located in the middle gastric body and was removed by endoscopic submucosal dissection. Histological examination revealed three morphologically distinct components: FGP, FGP with large cysts, and PGA. A genetic analysis identified a truncating APC mutation in all the three components, supporting their histogenetic relationship. Additionally, a GNAS mutation was detected in two components, FGP with large cysts and PGA, whereas a KRAS mutation was exclusively found in the PGA component. Thus, despite the unusual presentation, the PGA component harbored prototypical genetic alterations. The differential genetic alterations observed in the three components imply that they represent stepwise progression from FGP to PGA.

Gastric Epithelial Polyps: When to Ponder, When to Panic

This review provides an overview of different types of gastric epithelial polyps. The polyps are classified based on their cell or epithelial compartment of origin. Some of these polyps can be considered reactive or nonneoplastic, whereas others are neoplastic in origin, are sometimes associated with a hereditary polyposis/cancer syndrome, and may have malignant potential. The aim of this review is to provide a pragmatic overview for the practicing pathologist about how to correctly diagnose and deal with gastric epithelial polyps and when (not) to ponder, and when (not) to panic.

Histological analysis of fundic gland polyps secondary to PPI therapy

AIMS

The aim of this study was to clarify the histopathological features of fundic gland polyps (FGPs) in patients treated with proton pump inhibitors (PPIs) and to investigate the mechanism of enlargement of FGPs after PPI treatment.

METHODS AND RESULTS

A total of 196 biopsy specimens of FGPs, which consisted of 87 FGPs in patients treated with PPIs (PPI group) and 109 FGPs in patients treated without PPIs (non-PPI group) were compared histologically using haematoxylin and eosin staining, Ki67 immunohistochemistry and multiplex immunohistochemical stain with Ki67, MUC5AC and MUC6. The significant histological features of FGPs in the PPI group were: larger size of dilated fundic gland cysts, larger number of foveolar and mixture type fundic gland cysts, foveolar cell hyperplasia, parietal cell protrusion, mononuclear cell infiltration and a higher percentage of Ki67-positive cells in the deeper layers of the glands. Multiplex immunohistochemical stain showed that Ki67-positive cells were also positive for MUC5AC, and the Ki67-positive rate was significantly higher in MUC5AC-positive cells of the PPI group than of the non-PPI group. Gene mutations of β-catenin were found in only 9.7% of FGPs in the PPI group.

CONCLUSIONS

Enlargement of fundic gland cysts due to foveolar cell proliferation and parietal cell protrusion might promote the enlargement of FGPs in patients treated with PPIs. β-catenin gene mutations might not be associated with these histological changes of FGPs after PPI treatment.

GASTRIC FUNDIC GLAND POLYPS: CAN HISTOLOGY BE USEFUL TO PREDICT PROTON PUMP INHIBITORS USE?

BACKGROUND

Fundic gland polyps allegedly increased in frequency in recent decades, and had attracted great attention due to possible association with prolonged proton pump inhibitor therapy. Prolonged use of this drug could cause parietal cell hyperplasia, obstruction of glandular lumen and cystic dilation of the gland.

OBJECTIVE

This study aims to analyze clinical and pathological features of fundic gland polyps in patients with and without proton pump inhibitor therapy in a selected population from Brazil.

METHODS

It was selected a sample of 101 Brazilian patients (78 females and 23 males), from a five years retrospective search of the files from a private pathology laboratory. The patients had an average age of 57 years and we included patients with a histological diagnosis of fundic gland polyp. The clinical data were obtained from their files and all histological slides were reviewed and examined with hematoxylin and eosin (HE) and Giemsa.

RESULTS

Information about the use or non-use of proton pump inhibitors (PPI) was obtained in 84 patient files. In 17 cases we could not determine if PPI were used or not. Among those in which the information was available, a positive history of anti-acid therapy was observed in 63 (75.0%) patients. Parietal cell hypertrophy/hyperplasia and parietal cell protrusions were detected in most slides. Histological findings were identical in PPI users and PPI negative patients. Helicobacter pylori infection was detected in just two samples. Epithelial dysplasia or adenocarcinoma were not observed in our cases. Histopathological analysis of fundic gland polyps could not distinguish between PPI and non-PPI related cases. Parietal cell cytoplasmic protrusions, an alleged marker of prolonged acid suppression therapy, was detected in both groups.

CONCLUSION

Histological features could not discriminate anti-acid therapy related fundic glands polyps in our patients.

No transformation of a fundic gland polyp with dysplasia into invasive carcinoma after 14 years of follow-up in a proton pump inhibitor-treated patient: A case report

A fundic gland polyp (FGP) is a common gastric polyp. Intraepithelial neoplasia in FGPs, referred to as FGP with dysplasia, is often seen in patients with familial adenomatous polyposis (FAP). In sporadic FGPs, low-grade dysplasia (LGD) is rare, and high-grade dysplasia (HGD) or carcinoma arising from sporadic FGPs is extremely rare. Because of this rarity, the prognosis and appropriate management of these lesions have not been clarified. In the present case, a sporadic FGP with LGD did not develop into invasive carcinoma, but contained foci of HGD 14 years after diagnosis. The biopsy specimen of the polyp taken at the first esophagogastroduodenoscopy 15 years earlier was diagnosed as FGP without dysplasia. At the second histological examination, LGD was found. Because the polyp increased in size during proton pump inhibitor therapy for 14 years, endoscopic mucosal resection was performed. The pathological diagnosis of the resected specimen was FGP with HGD mixed in LGD, with no invasive carcinoma. Dysplasia in FGPs might have less malignant potential regardless of dysplasia or size.

Chibby is a weak regulator of β-catenin activity in gastric epithelium

The canonical Wnt-β-catenin pathway is important in normal development. Mutations in β-catenin or proteins involved with regulating its phosphorylation or localization result in its nuclear accumulation where it activates its target genes and stimulates cell proliferation. This pathway is dysregulated in many different types of cancer, including gastric cancer (GC). Chibby (Cby) is a 14-kDa protein that inhibits β-catenin localization to the nucleus and represses β-catenin-induced transcriptional activity. In the current study, we examined the expression and function of Cby in normal and cancerous human gastric tissue. Reverse-transcription polymerase chain reaction and immunohistochemistry revealed that Cby is expressed in human stomach and localized to glandular elements. Immunohistochemical staining intensity of Cby was decreased in GC tissue when compared with normal gastric epithelium. In AGS cells, a human gastric carcinoma cell line, Cby expression was low. Stable AGS cell transfectants overexpressing Cby were prepared. Cby overexpression did not affect proliferation rates or β-catenin levels. However, confocal microscopy and subcellular fractionation studies revealed that Cby overexpression resulted in a small decrease in nuclear β-catenin. Moreover, Cby overexpression caused a molecular weight shift in nuclear β-catenin and resulted in decreased β-catenin signaling in AGS cells as measured by the TopFlash assay. However, Cby overexpression did not affect c-Myc protein levels. To conclude, Cby expression was decreased in GC samples and Cby expression altered β-catenin localization in cultured GC cells. However, Cby did not affect cell proliferation rates or β-catenin-induced protein expression. Cby may be involved in the early events in the pathogenesis of GC.

Comparison of dysplastic fundic gland polyps in patients with and without familial adenomatous polyposis

AIMS

Dysplastic fundic gland polyps (d-FGPs) typically arise in patients with familial adenomatous polyposis (FAP) but may occur in non-syndromic patients. They rarely become malignant, but their significance is unclear, especially in non-syndromic patients. We aimed to compare d-FGPs in patients with and without FAP, using clinicopathologic findings and β-catenin immunohistochemistry (IHC).

METHODS AND RESULTS

We identified 124 fundic gland polyps with low-grade dysplasia (LGD) or high-grade dysplasia (HGD) or indefinite for dysplasia (IFD) from 66 patients (27 with FAP; 39 non-syndromic). We recorded patient sex, age at first d-FGP, time until subsequent d-FGP (if any), history of non-gastric cancer (no patients had gastric cancer), proton-pump inhibitor use, and the presence of Helicobacter pylori. β-Catenin IHC was performed on cases with available blocks. The mean age at d-FGP diagnosis was 31 years for FAP patients and 61 years for non-syndromic patients (P < 0.0001). Sixteen FAP patients (59%) developed at least one subsequent d-FGP, as compared with 10 (27%) non-syndromic patients (P = 0.0099). The median time between d-FGP detection was 11.5 months in FAP patients and 7 months in non-syndromic patients (P = 0.82). Six FAP patients (22%) and 17 non-syndromic patients (44%) had non-gastric malignancies (P = 0.11). β-Catenin IHC showed nuclear positivity in 14 of 112 (13%) d-FGPs: 12 of 94 with LGD, two of three with HGD, and none of 15 with IFD polyps.

CONCLUSIONS

Familial adenomatous polyposis patients develop d-FGPs earlier and more often develop additional ones than non-syndromic patients. d-FGPs in FAP and non-syndromic patients have similar low rates of β-catenin nuclear IHC positivity. FAP and non-syndromic patients developed non-gastric cancers at similar rates, suggesting that d-FGPs may portend a general increased risk of carcinogenesis in non-syndromic patients.

Fundic Gland Polyps in the Pediatric Population: Clinical and Histopathologic Studies

We retrospectively studied the clinical and histologic features of pediatric fundic gland polyps (FGPs) in 16 patients. FGPs had an endoscopic prevalence of 0.25% in 8527 pediatric gastric biopsies. Five patients had familial adenomatous polyposis (FAP). The median age of onset was 17.7 years in FAP and 17.3 years in sporadic patients. All syndromic patients were asymptomatic and FGPs were identified during surveillance for existing or concurrent colon polyps. They did not take antacids. In comparison, all 11 sporadic FGPs were identified during evaluation of symptomatic patients who had taken antacids (median duration 21 months). Syndromic FGPs can be multiple at single endoscopy and were more likely to recur, while sporadic FGPs were often single. None of the sporadic patients had recurrence of FGPs or a subsequent diagnosis of FAP during a median follow-up of 20.5 months. The dilated fundic glands were lined by parietal and chief cells only in a majority (22/41, 53.7%) of syndromic FGPs, while additional tall mucinous lining cells were found in all sporadic FGPs. Syndromic FGPs did not have parietal cell hypertrophy in the background oxyntic mucosa. Nuclear immunopositivity for beta-catenin was essentially absent in all the FGPs. In conclusion, FGPs were rare in pediatric patients. In syndromic patients, FGPs are asymptomatic and did not precede colon polyps. Prolonged antacid intake seems to be associated with development of sporadic FGPs. Cellular components of dilated fundic glands and background parietal cell hypertrophy can be useful features to eliminate concern for syndromic polyposis.

Epigenetic regulation of Wnt/β-catenin signal-associated genes in gastric neoplasia of the fundic gland (chief cell-predominant) type

Gastric neoplasia of the fundic gland (chief cell-predominant) type (GNCCP) is a rare variant of gastric tumor. This tumor is associated with activation of the Wnt/β-catenin signaling pathway; however, the mechanisms underlying this activation remain unknown. To elucidate potential roles of Wnt/β-catenin signal-associated gene methylation in GNCCP, we performed β-catenin immunostaining and methylation-specific polymerase chain reaction (PCR) for their associated genes, including SFRPs, APC, AXIN2, and MCC, in 26 GNCCPs [i.e., 11 intramucosal (GNCCP-Ms) and 15 submucosal tumors (GNCCP-SMs)], and compared with 27 fundic gland polyps (FGPs), 12 FGPs with dysplasia (FGP-Ds), 27 conventional gastric adenocarcinomas (CGAs). Nuclear β-catenin labeling indices were higher in GNCCPs and CGAs than in FGPs and FGP-Ds. SFRPs, APC, and AXIN2 were more frequently methylated in GNCCPs and CGAs (SFRP1, 88%/96%; SFRP2, 85%/93%; SFRP4, 73%/81%; APC, 81%/81%; AXIN2, 81%/85%; respectively) than in FGPs and FGP-Ds (37%/50%; 41%/42%; 41%/58%; 37%/33%; 41%/50%; respectively). A significant correlation was seen between nuclear β-catenin expression and methylation of SFRP1 in GNCCPs. Furthermore, nuclear β-catenin expression was significantly frequent in high-methylated GNCCPs than in low-methylated tumors. In conclusion, our results suggest that activation of this pathway, mediated by gene methylation, may be associated with progression of some GNCCP cases, similar to CGAs.

Sporadic Fundic Gland Polyps With Low-Grade Dysplasia: A Large Case Series Evaluating Pathologic and Immunohistochemical Findings and Clinical Behavior

OBJECTIVES

Fundic gland polyps (FGPs) occur in two clinical settings, sporadic and syndromic. Epithelial dysplasia is rare in sporadic FGPs, and progression data from large series are lacking. The aim of this study was to evaluate the clinical, morphologic, and immunohistochemical features in a large series of sporadic FGPs with epithelial dysplasia.

METHODS

We studied 85 patients with FGPs with low-grade dysplasia (FGPD), including 62 patients with sporadic and 23 with syndromic FGPDs.

RESULTS

Sixty-two patients with sporadic FGPD comprised 29 men and 33 women with a median age of 56 years. The indications for endoscopy were heartburn and follow-up of Barrett esophagus, and 49 patients had a history of proton pump inhibitor use. Morphologically, sporadic and syndromic FGPDs were similar. Immunohistochemical staining for p53 was normal (weak 1+) in all polyps, Ki-67 immunohistochemistry showed staining in the mucus neck and surface epithelium, and nuclear accumulation of β-catenin was observed in 9 of 40 sporadic FGPDs. Twenty-six (42%) patients with sporadic FGPDs had follow-up esophagogastroduodenoscopies with biopsies after a mean period of 14.8 months (nine with more than one follow-up): nine (35%) had no additional polyps, 13 (50%) had nondysplastic sporadic FGPs, and four (15%) had sporadic FGPDs.

CONCLUSIONS

Sporadic FGPDs were seen primarily in middle-aged patients with gastroesophageal reflux. Follow-up data support the indolent nature of these polyps.

Mutation spectrum in the Wnt/β-catenin signaling pathway in gastric fundic gland-associated neoplasms/polyps

Frequent activation of the Wnt/β-catenin signaling pathway has recently been demonstrated in gastric adenocarcinoma/neoplasia of chief cell predominant type (GA-CCP/GN-CCP) with submucosal involvement. In this study, we examined the activation status of the Wnt/β-catenin signaling pathway in GN-CCP without submucosal involvement, which is referred to as gastric dysplasia-CCP (GD-CCP). We also examined β-catenin expression and the mutation spectrum of PPP2R1A and Wnt pathway genes in 11 cases of GD-CCP, 25 cases of gastric polyps of fundic gland type (GPs-FG), and 21 cases of GPs-FG with dysplasia (GP-FGD). β-catenin nuclear staining was observed in 3 cases of GD-CCP, none of GPs-FG, and 6 cases of GPs-FGD. Mutations in Wnt pathway genes, including PPP2R1A, were observed in 4 cases of GDs-CCP, 10 cases of GPs-FG, and 7 cases of GPs-FGD. Two of these seven GPs-FGD cases showed β-catenin nuclear staining. However, none of the 4 GD-CCP cases with mutations or the 10 GPs-FG cases with mutations showed β-catenin nuclear staining. PPP2R1A mutations were observed in 1 GD-CCP case and 1 GPs-FGD case. Although the mutation spectra of the Wnt pathway genes in GD-CCP and GP-FG differed, based on the absence of β-catenin nuclear staining despite the genetic alterations, GD-CCP is more similar to GP-FG than to GN-CCP, which shows β-catenin nuclear staining and submucosal involvement. Activation of the Wnt/β-catenin signaling by the β-catenin nuclear transition may be required during progression from GD-CCP to GN-CCP. Furthermore, this is the first report describing PPP2R1A mutations in gastric fundic gland-associated neoplasms.

GNAS mutation as an alternative mechanism of activation of the Wnt/β-catenin signaling pathway in gastric adenocarcinoma of the fundic gland type

Gastric adenocarcinoma of the fundic gland type (GAFG) is a rare variant of gastric tumor. We have recently reported the frequent accumulation of β-catenin in GAFGs and showed that approximately half of the cases studied harbored at least 1 mutation in CTNNB1/AXINs/APC, leading to the constitutive activation of the Wnt/β-catenin pathway. However, the mechanisms of Wnt signaling activation in the remaining cases are unknown. Accumulating evidence showed that the activating mutation in GNAS promotes tumorigenesis via the activation of the Wnt/β-catenin pathway or the ERK1/2 MAPK pathway. Therefore, we analyzed the mutations in GNAS (exons 8 and 9) and in KRAS (exon 2) in 26 GAFGs. Immunohistochemistry revealed nuclear β-catenin expression in 22 of 26 GAFGs, and 10 (38.5%) of 26 cases harbored at least 1 mutation in CTNNB1/AXINs/APC. Activating mutations in GNAS were found in 5 (19.2%) of 26 GAFGs, all of which harbored R201C mutations. Activating mutations in KRAS were found in 2 (7.7%) of 26 GAFGs, and both of these also contained GNAS activating mutations. Four of 5 cases with GNAS mutation showed nuclear β-catenin expression, and presence of GNAS mutation was associated with β-catenin nuclear expression (P = .01). Furthermore, 3 of these 4 cases did not harbor mutations in CTNNB1, APC, or AXINs, suggesting that mutations in the Wnt component genes and those in GNAS occur almost exclusively. These results suggest that GNAS mutation might occur in a small subset of GAFG as an alternative mechanism of activating the Wnt/β-catenin signaling pathway.

Morphology and natural history of familial adenomatous polyposis-associated dysplastic fundic gland polyps

AIMS

Most patients with familial adenomatous polyposis (FAP) develop gastric fundic gland polyps, with many displaying low-grade dysplasia. This study evaluates the natural history and morphological phenotype of dysplasia in FAP-associated fundic gland polyps.

METHODS AND RESULTS

Patients with FAP and dysplastic fundic gland polyps (n = 24) were identified. Twenty-two of 24 FAP-associated dysplastic fundic gland polyps showed a gastric phenotype and two had mixed phenotype. During a mean 6.1-year follow-up (range 0.8-12.6 years) and 5.7 endoscopies (range 2-22), one patient (4%) was diagnosed with a fundic gland polyp with high-grade dysplasia, while 23 patients (96%) in this cohort had either no dysplasia or persistent low-grade dysplasia. Contemporary patients with sporadic fundic gland polyps with low-grade dyplasia had similar morphology and outcomes to the FAP-associated fundic gland polyp cohort. Dysplasia in fundic gland polyps (FAP-associated and sporadic) was associated less frequently with intestinal phenotype, high-grade dysplasia and the finding of concurrent or subsequent carcinoma compared to contemporary patients with sporadic gastric dysplasia not occurring in fundic gland polyps.

CONCLUSIONS

This cohort of patients with FAP-associated dysplastic fundic gland polyps rarely developed high-grade dysplasia and gastric adenocarcinoma was absent.

Alteration in the Wnt/β-catenin signaling pathway in gastric neoplasias of fundic gland (chief cell predominant) type

Gastric neoplasia of chief cell-predominant type (GN-CCP) has been reported as a new, rare variant of gastric tumor. GN-CCPs were defined as tumors consisting of irregular anastomosing glands of columnar cells mimicking chief cells of fundic gland with nuclear atypia and prolapse-type submucosal involvement. We comparatively evaluated clinicopathologic features between 31 GN-CCPs and 130 cases of conventional gastric adenocarcinoma invading into submucosa (CGA-SM) in addition to nuclear β-catenin immunolabeling and direct sequencing of members of the Wnt/β-catenin pathway, CTNNB1, APC, and AXIN, in a subset of these tumors. GN-CCP presented as small protruded lesions located in the upper third of the stomach, with minimal involvement into the submucosa and rare lymphovascular invasion. None of the lesions have demonstrated a recurrence of disease or metastasis on follow-up. Nuclear β-catenin immunolabeling was higher in GN-CCP (labeling index [LI]: median, 19.3%; high expresser [LI >30%], 7/27 cases [26%]) than CGA-SM (median LI, 14.7%; high expresser, 1/19 cases [6%]). Missense mutation of APC was observed in 1 GN-CCP but not CGA-SM. Missense or nonsense mutations of CTNNB1 and AXIN1 were higher in GN-CCPs (14.8%, both) than CGA-SMs (5.3%, both). Missense mutations of AXIN2 were higher in GN-CCPs (25.9%) than in CGA-SMs (10.5%). Overall, 14 (51.9%) of 27 GN-CCPs and 5 (26.3%) of 19 CGA-SM cases harbored at least 1 of these gene mutations. In conclusion, GN-CCPs as a unique variant of nonaggressive tumor are characterized by nuclear β-catenin accumulation and mutation of CTNNB1 or AXIN gene, suggesting activation of the Wnt/β-catenin pathway.

Acute WNT signalling activation perturbs differentiation within the adult stomach and rapidly leads to tumour formation

A role for WNT signalling in gastric carcinogenesis has been suggested due to two major observations. First, patients with germline mutations in adenomatous polyposis coli (APC) are susceptible to stomach polyps and second, in gastric cancer, WNT activation confers a poor prognosis. However, the functional significance of deregulated WNT signalling in gastric homoeostasis and cancer is still unclear. In this study we have addressed this by investigating the immediate effects of WNT signalling activation within the stomach epithelium. We have specifically activated the WNT signalling pathway within the mouse adult gastric epithelium via deletion of either glycogen synthase kinase 3 (GSK3) or APC or via expression of a constitutively active β-catenin protein. WNT pathway deregulation dramatically affects stomach homoeostasis at very short latencies. In the corpus, there is rapid loss of parietal cells with fundic gland polyp (FGP) formation and adenomatous change, which are similar to those observed in familial adenomatous polyposis. In the antrum, adenomas occur from 4 days post-WNT activation. Taken together, these data show a pivotal role for WNT signalling in gastric homoeostasis, FGP formation and adenomagenesis. Loss of the parietal cell population and corresponding FGP formation, an early event in gastric carcinogenesis, as well as antral adenoma formation are immediate effects of nuclear β-catenin translocation and WNT target gene expression. Furthermore, our inducible murine model will permit a better understanding of the molecular changes required to drive tumourigenesis in the stomach.

Efficient Genetic Analysis of Microdissected Samples by Agarose-Bead Method: Alterations of β-Catenin Gene in Fundic Gland Polyp and Heterotopic Gastric Mucosa of Duodenum

Molecular genetic analyses of archival formalin-fixed, paraffin-embedded (FFPE) pathological specimens taken at biopsy or autopsy, are occasionally compromised because the DNA molecules therein are inevitably degraded. Furthermore, since these tissue samples comprise various cell types, the analyses based on mixtures of such heterogeneous populations often fail to reflect the nature of the affected cells. In the present study, to elucidate the contribution of β-catenin gene mutation to the fundic gland polyp and the heterotopic gastric mucosa in the duodenum, we successfully introduced an agarose-bead mediated technique as an effectual tool for retrospective morphology-oriented genetic analyses. Microdissected samples were embedded in low-melting agarose, and directly treated with proteinase K. A fragment of the agarose-bead was used as a template for polymerase chain reaction to analyze β-catenin mutation. Of the six cases of heterotopic gastric mucosa in the duodenum associated with fundic gland polyps, one showed a common 1-bp missense mutation at codon 37 shared by both the fundic gland polyp and the heterotopic gastric mucosa. Alternatively, a 1-bp silent mutation at codon 33 and missense mutation at codon 32 were identified only in the heterotopic gastric mucosa. Agarose-bead mediated technique shows superior sensitivity to the previously described techniques and is an effectual tool for retrospective morphology-oriented genetic analyses using a large number of archival pathological samples stored for long periods in the pathology laboratory.

Chronic proton pump inhibitor therapy associated with increased development of fundic gland polyps

BACKGROUND

Fundic gland polyps (FGP) have been implicated with long-term proton pump inhibitor (PPI) use.

AIMS

We attempted to investigate the impact of length and dosage of PPI therapy on the development of FGP.

METHODS

A retrospective cohort study of all patients who had gastric polyps removed during elective upper endoscopy between March and September 2007 as part of a prior prospective study protocol was carried out. FGP were determined histologically. Prior to endoscopy, all patients completed a questionnaire regarding PPI use and length of therapy (no PPI use, 1-48 months, >48 months). The dosage of PPI was obtained via a thorough chart review of electronic medical records.

RESULTS

Three hundred and eighty-five patients completed upper endoscopy and a questionnaire reporting PPI use (252 [65.4%] patients on PPI). On endoscopy, 55 patients had polyps, with the majority (43/55, 78%) being FGP, resulting in an overall prevalence of 11.1% (43/385). On univariate analysis, FGP were associated with Caucasian race (15 vs. 6%; P=0.009) and chronic PPI therapy (>48 months) (31.9 vs. 7.5%, P<0.001). There was a significant linear-by-linear association between PPI dosage and FGP prevalence (no PPI use, 7.5%; once daily, 10.8%; twice daily 17.4%, P=0.026). On logistic regression, the only independent predictor of FGP was duration of PPI use >48 months (P=0.001, odds ratio [OR] 4.7 [2.0-12.9]).

CONCLUSIONS

The only independent predictor of FGP development in our study was duration of PPI therapy greater than 48 months. Increased dosage of therapy did not significantly impact the development of FGP.

High-grade dysplasia associated with fundic gland polyposis in a familial adenomatous polyposis patient, with special reference to APC mutation profiles

We report a patient with familial adenomatous polyposis who developed high-grade dysplasia against a background of fundic gland polyposis. Two large high-grade dysplasia lesions were found in the gastric body, where numerous fundic gland polyps were present. In both lesions, the dysplastic epithelium covered non-neoplastic oxyntic glands that occasionally exhibit cystic changes. A genetic analysis for APC (adenomatous polyposis coli) revealed a somatic 50-bp deletion involving codons 1502-1517 and 2-bp deletion at codon 1465 in each lesion of high-grade dysplasia. In contrast, six of the 18 fundic gland polyps were found to harbor an identical mutation: 1-bp insertion at codon 1556. Both lesions of high-grade dysplasia and the fundic gland polyps were similarly located in the fundic gland area and were caused by the inactivation of APC; however, their mutation profiles of APC were different. These results imply that fundic gland polyps and high-grade dysplasia of the stomach have distinct preferences for APC genotypes in their development.

Immunohistochemical evaluation of adenomatous polyposis coli, beta-catenin, c-Myc, cyclin D1, p53, and retinoblastoma protein expression in syndromic and sporadic fundic gland polyps

Syndromic and sporadic fundic gland polyps are morphologically indistinguishable but may arise via different pathogenetic mechanisms involving mutations of the adenomatous polyposis coli (APC) and its downstream target beta-catenin genes. Although a higher frequency of dysplasia has been reported in syndromic forms, the risk of developing invasive carcinoma is exceedingly low. The current study was designed to investigate whether syndromic and sporadic fundic gland polyps differ in protein expression of a number of genes that are thought to be important in the control of neoplastic transformation. A total of 262 fundic gland polyps, including 155 syndromic polyps obtained from 35 patients with familial adenomatous polyposis or Gardner's syndrome and 107 sporadic polyps randomly selected from 45 patients with gastroesophageal reflux disease or Barrett's esophagus, were included in this study. Immunohistochemical evaluation showed that loss of immunoreactivity to the antibody against the carboxyl terminus of the APC protein, presumably resulting from APC gene mutations, was more frequent in syndromic than in sporadic cases (40% versus 6.7%, P<0.001). However, immunostaining failed to show aberrant nuclear localization of beta-catenin, a protein regulated by APC, in any of the polyps, irrespective of syndromic or sporadic types. Instead, positive membranous staining for beta-catenin was observed in all the cases. In addition, the expression characteristics of 2 other proteins, c-Myc and cyclin D1, whose genes have been reported to be transcriptionally regulated by the APC/beta-catenin pathway, were similar in these two types of polyps. Furthermore, all cases, including those harboring dysplasia, showed negative nuclear staining for p53 and positive nuclear staining for retinoblastoma (RB). Taken together, these data show a lack of dysregulation in the APC/beta-catenin signaling pathway and in the expression of p53 and RB in fundic gland polyps despite a high frequency of somatic mutations of the APC and beta-catenin genes reported in these polyps. These findings may explain at least in part why fundic gland polyps show a negligible malignant potential even in the presence of dysplasia.

High-grade dysplasia in sporadic fundic gland polyps: a case report and review of the literature

We present a case of fundic gland polyps (FGPs) containing high-grade dysplasia in a 68-year-old man. High-grade dysplasia, and even gastric adenocarcinoma, associated with FGPs have been described in patients with familial adenomatous polyposis (FAP) and attenuated familial adenomatous polyposis (AFAP) but never in non-FAP patients. Two colonoscopies in the past six years virtually rule out FAP and AFAP in our patient. Dysplasia in FGPs from non-FAP patients is extremely rare, and until now only cases of low-grade dysplasia have been described. The literature on dysplasia in FGPs is reviewed briefly. Additional immunohistochemical investigations in this case showed nuclear staining of beta-catenin, increased proliferation and apoptosis in the dysplastic areas of the FGPs. Our case suggests that the malignant potential of FGPs is not limited to FAP-associated FGPs.

Cell adhesion system and human cancer morphogenesis

Cell-cell adhesion determines the polarity of cells and participates in the maintenance of the cell societies called tissues. Cell-cell adhesiveness is generally reduced in human cancers. Reduced intercellular adhesiveness allows cancer cells to disobey the social order, resulting in destruction of histological structure, which is the morphological hallmark of malignant tumors. Reduced intercellular adhesiveness is also indispensable for cancer invasion and metastasis. A tumor-suppressor gene product, E-cadherin, and its undercoat proteins, catenins, which connect cadherins to actin filaments, are located at lateral borders, concentrating on adherens junctions, of epithelial cells and establish firm cell-cell adhesion. The E-cadherin cell adhesion system in cancer cells is inactivated by various mechanisms that reflect the morphological and biological characteristics of the tumor. Silencing of the E-cadherin gene by DNA hypermethylation around the promoter region occurs frequently, even in precancerous conditions. In diffuse infiltrating cancers, mutations are found in the genes for E-cadherin and alpha- and beta-catenins. At the invading front of cancers, the E-cadherin cell adhesion system is inactivated by tyrosine phosphorylation of beta-catenin; an oncogene product, c-erbB-2 protein, is found to associate directly with beta-catenin. The E-cadherin cell adhesion system cross-talks with the Wingless/Wnt signaling pathway through beta-catenin, and expression of genes, which participate in cancer morphogenesis, may be regulated in conjunction with the Wingless/Wnt signaling pathway. Dysadherin, a newly identified cancer-associated cell membrane glycoprotein, down-regulates E-cadherin and promotes cancer metastasis. In conclusion, inactivation of the E-cadherin cell adhesion system by both genetic and epigenetic mechanisms plays a significant role during multistage human carcinogenesis.

Fundic gland polyps (Elster's cysts) of the gastric mucosa. A marker for colorectal epithelial neoplasia?

The results of several retrospective studies allow us to conclude that the detection of fundic gland polyps (Elster's cysts) is associated with an increased incidence of colorectal tumors. In this survey, we present the results of a prospective study investigating such a possible relationship. A total of 144 patients were investigated, of whom 80 had fundic gland polyps of the gastric corpus mucosa. Sixty-four of these patients underwent a colonoscopy, whereas the other 64 patients belonged to a sex- and age-matched control group with no fundic gland polyps. In the group with known fundic gland polyps, colorectal neoplasias were found in 29 (45.3%) patients. Eight of these patients had (12.5%) adenocarcinomas, 3 (4.7%) had high-grade intraepithelial neoplasia, and 18 (28.1%) had tubular adenomas. In one patient, a synchronous carcinoma of the rectum and the colon was detected. In comparison, 6 patients of the control group (9.3%) developed tubular adenomas and 9 (14.1%) had hyperplastic polyps of the colonic and rectal mucosa. Our results suggest that it is necessary to conduct a careful diagnostic work-up of the colon in patients with gastric fundic gland polyps.

Caught up in a Wnt storm: Wnt signaling in cancer

The Wnt signaling pathway, named for its most upstream ligands, the Wnts, is involved in various differentiation events during embryonic development and leads to tumor formation when aberrantly activated. Molecular studies have pinpointed activating mutations of the Wnt signaling pathway as the cause of approximately 90% of colorectal cancer (CRC), and somewhat less frequently in cancers at other sites, such as hepatocellular carcinoma (HCC). Ironically, Wnts themselves are only rarely involved in the activation of the pathway during carcinogenesis. Mutations mimicking Wnt stimulation-generally inactivating APC mutations or activating beta-catenin mutations-result in nuclear accumulation of beta-catenin which subsequently complexes with T-cell factor/lymphoid enhancing factor (TCF/LEF) transcription factors to activate gene transcription. Recent data identifying target genes has revealed a genetic program regulated by beta-catenin/TCF controlling the transcription of a suite of genes promoting cellular proliferation and repressing differentiation during embryogenesis, carcinogenesis, and in the post-embryonic regulation of cell positioning in the intestinal crypts. This review considers the spectra of tumors arising from active Wnt signaling and attempts to place perspective on recent data that begin to elucidate the mechanisms prompting uncontrolled cell growth following induction of Wnt signaling.

Beta-catenin mutations in pulmonary blastomas: association with morule formation

To elucidate the contribution of beta-catenin gene mutation to the development of pulmonary blastomas, we analysed mutations in three well-differentiated fetal adenocarcinomas (WDFAs) and six biphasic pulmonary blastomas (BPBs). For comparison, eight clear-cell adenocarcinomas with fetal lung features were also examined. beta-Catenin gene mutations were found in all three WDFAs, two BPBs, and none of the clear-cell adenocarcinomas with fetal lung features. All tumours with mutations had a common histological feature, namely morule formation, and showed a characteristic heterogeneous beta-catenin expression pattern that was revealed by immunohistochemistry. Strong nuclear/cytoplasmic expression of beta-catenin was seen in clustered cells in the morular areas and in single cells in glands, and was associated with neuroendocrine differentiation. As beta-catenin mutations are rare among lung tumours, this distinctive genetic feature, which is also immunohistochemically detectable as overexpression with a heterogeneous pattern, has diagnostic significance. The presence of this common genetic alteration found in both WDFA and BPB implies a histogenetic linkage between these tumours.

Wnt/beta-catenin/tcf signaling: a critical pathway in gastrointestinal tumorigenesis

Cancers of the gastrointestinal tract, including the liver, bile ducts, and pancreas, constitute the largest group of malignant tumors. Colorectal cancer is one of the most common neoplastic diseases in Western countries and one of the leading causes of cancer-related deaths. Inactivation of the adenomatous polyposis coli (APC) tumor-suppressor gene during early adenoma formation is thought to be the first genetic event in the process of colorectal carcinogenesis followed by mutations in oncogenes like K-Ras and tumor-suppressor genes like p53. Identification of the interaction of APC with the proto-oncogene beta-catenin has linked colorectal carcinogenesis to the Wnt-signal transduction pathway. The main function of APC is thought to be the regulation of free beta-catenin in concert with the glycogen synthase kinase 3beta (GSK-3beta) and Axin proteins. Loss of APC function, inactivation of Axin or activating beta-catenin mutations result in the cellular accumulation of beta-catenin. Upon translocation to the nucleus beta-catenin serves as an activator of T-cell factor (Tcf)-dependent transcription leading to an increased expression of several specific target genes including c-Myc, cyclin D1, MMP-7, and ITF-2. While APC mutations are almost exclusively found in colorectal cancers, deregulation of Wnt/beta-catenin/Tcf signaling is also common in other gastrointestinal and extra-gastrointestinal human cancers. In a fraction of hepatocellular carcinomas the Wnt pathway is deregulated by inactivation of Axin or stabilizing mutations of beta-catenin. The majority of hepatoblastomas and a group of gastric cancers also carry beta-catenin mutations. Clearly, this pathway harbors great potential for future applications in cancer diagnostics, staging, and therapy.

Craniopharyngiomas of adamantinomatous type harbor beta-catenin gene mutations

Craniopharyngioma is a rare tumor occurring in the sellar region comprising 3% of all intracranial tumors. To elucidate the contribution of beta-catenin gene mutation to tumorigenesis, we examined genetic alterations and expression of beta-catenin in 10 cases of adamantinomatous and 6 cases of papillary craniopharyngiomas. Beta-catenin gene mutations were found in all of the adamantinomatous and none of the papillary craniopharyngiomas. Immunohistochemically, all cases of adamantinomatous craniopharyngioma showed cytoplasmic and nuclear expression of beta-catenin. In contrast, papillary craniopharyngiomas showed exclusively membranous expression. The results suggest that adamantinomatous- and papillary-type craniopharyngiomas are not only clinicopathologically, but also genetically, distinctive variants. Mutation of the beta-catenin gene therefore seems to play an important role in the tumorigenesis of adamantinomatous craniopharyngioma. Among the adamantinomatous-type tumors, beta-catenin-positive mesenchymal cells were observed in two cases. Microdissection-based mutational analysis revealed that these mesenchymal cells also harbor the same beta-catenin gene mutations as those of epithelial cells, suggesting their tumorous nature. Thus, at least a subset of adamantinomatous craniopharyngioma is considered to be biphasic.

Sporadic fundic gland polyps with epithelial dysplasia : evidence for preferential targeting for mutations in the adenomatous polyposis coli gene

Gastric fundic gland polyps (FGPs) occur in two distinct clinicopathological scenarios: sporadic and familial adenomatous polyposis (FAP) associated. FAP-associated FGPs arise through somatic second hit alterations of the adenomatous polyposis coli (APC) gene and frequently demonstrate epithelial dysplasia (Am J Pathol 2000, 157:747-754). Sporadic FGPs, in contrast, tend to contain beta-catenin gene mutations and only infrequently show dysplasia (Am J Pathol 2001, 158:1005-1010). However, sporadic FGPs with dysplasia have not been previously investigated. We studied 13 sporadic FGPs with surface/foveolar low-grade dysplasia or changes indefinite for dysplasia for alterations in the APC/beta-catenin pathway, using chromosome 5q allelic loss assays and direct DNA sequencing of the mutation cluster region in exon 15 of APC and the phosphorylation region in exon 3 of beta-catenin. In addition, to evaluate for possible additional genetic alterations in FGPs, all cases were evaluated for microsatellite instability using fluorescent-based amplification of a standard panel of five microsatellite markers. Alterations in APC were present in seven (53.8%) FGPs, including two cases with bi-allelic APC inactivation (truncating intragenic mutation plus 5q allelic loss), two cases with APC mutation only, and three cases with 5q allelic loss only. In contrast, only two (15.4%) FGPs contained stabilizing beta-catenin mutations. All 13 FGPs were microsatellite stable. These results indicate that sporadic FGPs with dysplasia/indefinite for dysplasia are molecularly similar to FAP-associated FGPs, and are dissimilar to the more common sporadic nondysplastic FGPs. Mutations in APC and beta-catenin, despite occurring in the same genetic pathway, show differing biological properties, a phenomenon that has previously been demonstrated in colorectal neoplasms. The lack of microsatellite instability in FGPs in this study and of K-ras mutations in a previous study suggests that secondary genetic alterations are rare in both dysplastic and nondysplastic FGPs.

Target disruption of the mutant beta-catenin gene in colon cancer cell line HCT116: preservation of its malignant phenotype

Most colorectal carcinomas harbor genetic alterations that result in stabilization of beta-catenin. A colorectal carcinoma cell line, HCT116, which has both mutated and wild-type beta-catenin genes, was engineered by homologous recombination to investigate the significance of beta-catenin gene mutation. As expected, the mutant allele-targeted clones showed decreased beta-catenin expression and downregulation of T-cell factor (TCF)/lymphoid enhancer factor (LEF)-dependent transcription. Morphologically, targeted clones were only minimally altered under usual culture conditions, but under low serum conditions, mutant allele-targeted clones still grew in plane, in contrast to parental cell line and wild allele-targeted clones, which formed spheroids. The mutant allele-targeted clones showed no significant changes in growth rate and anchorage-independent growth in vitro, and displayed rather increased growth in vivo. Although beta-catenin stabilization affects some biological characteristics including adhesive properties, it may not have growth-promoting effects at least in some colorectal carcinomas.

Genetics--cellular basis

Colorectal carcinogenesis is a multistep process during which the specialised epithelial cells of intestinal mucosa surface (e.g. colonocytes) accumulate a series of genetic and epigenetic events which lead to a perturbation of their normal cellular functions and turnover. This review will address the mechanisms and biological effects of these abnormalities on the growth control, differentiation, adhesion and survival of the colonocytes.