Acquisition of WNT Pathway Gene Alterations Coincides With the Transition From Precursor Polyps to Traditional Serrated Adenomas. Am J Surg Pathol. 2019;43:132-139. [PMID: 30179900 DOI: 10.1097/pas.0000000000001149]

RSPO3 induced by Helicobacter pylori extracts promotes gastric cancer stem cell properties through the GNG7/β-catenin signaling pathway

BACKGROUND

Helicobacter pylori (H. pylori) accounts for the majority of gastric cancer (GC) cases globally. The present study found that H. pylori promoted GC stem cell (CSC)-like properties, therefore, the regulatory mechanism of how H. pylori promotes GC stemness was explored.

METHODS

Spheroid-formation experiments were performed to explore the self-renewal capacity of GC cells. The expression of R-spondin 3 (RSPO3), Nanog homeobox, organic cation/carnitine transporter-4 (OCT-4), SRY-box transcription factor 2 (SOX-2), CD44, Akt, glycogen synthase kinase-3β (GSK-3β), p-Akt, p-GSK-3β, β-catenin, and G protein subunit gamma 7 (GNG7) were detected by RT-qPCR, western blotting, immunohistochemistry (IHC), and immunofluorescence. Co-immunoprecipitation (CoIP) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) were performed to identify proteins interacting with RSPO3. Lentivirus-based RNA interference constructed short hairpin (sh)-RSPO3 GC cells. Small interfering RNA transfection was performed to inhibit GNG7. The in vivo mechanism was verified using a tumor peritoneal seeding model in nude mice.

RESULTS

H. pylori extracts promoted a CSC-like phenotype in GC cells and elevated the expression of RSPO3. RSPO3 knockdown significantly reduced the CSC-like properties induced by H. pylori. Previous studies have demonstrated that RSPO3 potentiates the Wnt/β-catenin signaling pathway, but the inhibitor of Wnt cannot diminish the RSPO3-induced activation of β-catenin. CoIP and LC-MS/MS revealed that GNG7 is one of the transmembrane proteins interacting with RSPO3, and it was confirmed that RSPO3 directly interacted with GNG7. Recombinant RSPO3 protein increased the phosphorylation level of Akt and GSK-3β, and the expression of β-catenin in GC cells, but this regulatory effect of RSPO3 could be blocked by GNG7 knockdown. Of note, GNG7 suppression could diminish the promoting effect of RSPO3 to CSC-like properties. In addition, RSPO3 suppression inhibited MKN45 tumor peritoneal seeding in vivo. IHC staining also showed that RSPO3, CD44, OCT-4, and SOX-2 were elevated in H. pylori GC tissues.

CONCLUSION

RSPO3 enhanced the stemness of H. pylori extracts-infected GC cells through the GNG7/β-catenin signaling pathway.

Downregulation of SMOC1 is associated with progression of colorectal traditional serrated adenomas

BACKGROUND

Aberrant DNA methylation is prevalent in colorectal serrated lesions. We previously reported that the CpG island of SMOC1 is frequently methylated in traditional serrated adenomas (TSAs) and colorectal cancers (CRCs) but is rarely methylated in sessile serrated lesions (SSLs). In the present study, we aimed to further characterize the expression of SMOC1 in early colorectal lesions.

METHODS

SMOC1 expression was analyzed immunohistochemically in a series of colorectal tumors (n = 199) and adjacent normal colonic tissues (n = 112).

RESULTS

SMOC1 was abundantly expressed in normal colon and SSLs while it was significantly downregulated in TSAs, advanced adenomas and cancers. Mean immunohistochemistry scores were as follows: normal colon, 24.2; hyperplastic polyp (HP), 18.9; SSL, 23.8; SSL with dysplasia (SSLD)/SSL with early invasive cancer (EIC), 15.8; TSA, 5.4; TSA with high grade dysplasia (HGD)/EIC, 4.7; non-advanced adenoma, 21.4; advanced adenoma, 11.9; EIC, 10.9. Higher levels SMOC1 expression correlated positively with proximal colon locations and flat tumoral morphology, reflecting its abundant expression in SSLs. Among TSAs that contained both flat and protruding components, levels of SMOC1 expression were significantly lower in the protruding components.

CONCLUSION

Our results suggest that reduced expression of SMOC1 is associated with progression of TSAs and conventional adenomas and that SMOC1 expression may be a biomarker for diagnosis of serrated lesions and risk prediction in colorectal tumors.

Discovering the Mutational Profile of Early Colorectal Lesions: A Translational Impact

Simple Summary

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Next-generation sequencing technologies have identified new candidate genes and deepened the knowledge of the molecular mechanisms underlying the progression of colonic adenomas towards CRC. The main genetic, epigenetic, and molecular alterations driving the onset and progression of CRC in both hereditary and sporadic settings have also been investigated. The evaluation of the CRC risk based on the molecular characterization of early pre-cancerous lesions may contribute to the development of targeted preventive strategies development, help define specific risk profiles, and identify patients who will benefit from targeted endoscopic surveillance.

Abstract

Colorectal cancer (CRC) develops through a multi-step process characterized by the acquisition of multiple somatic mutations in oncogenes and tumor-suppressor genes, epigenetic alterations and genomic instability. These events lead to the progression from precancerous lesions to advanced carcinomas. This process requires several years in a sporadic setting, while occurring at an early age and or faster in patients affected by hereditary CRC-predisposing syndromes. Since advanced CRC is largely untreatable or unresponsive to standard or targeted therapies, the endoscopic treatment of colonic lesions remains the most efficient CRC-preventive strategy. In this review, we discuss recent studies that have assessed the genetic alterations in early colorectal lesions in both hereditary and sporadic settings. Establishing the genetic profile of early colorectal lesions is a critical goal in the development of risk-based preventive strategies.

Mutations and mechanisms of WNT pathway tumour suppressors in cancer

Mutation-induced activation of WNT-β-catenin signalling is a frequent driver event in human cancer. Sustained WNT-β-catenin pathway activation endows cancer cells with sustained self-renewing growth properties and is associated with therapy resistance. In healthy adult stem cells, WNT pathway activity is carefully controlled by core pathway tumour suppressors as well as negative feedback regulators. Gene inactivation experiments in mouse models unequivocally demonstrated the relevance of WNT tumour suppressor loss-of-function mutations for cancer growth. However, in human cancer, a far more complex picture has emerged in which missense or truncating mutations mediate stable expression of mutant proteins, with distinct functional and phenotypic ramifications. Herein, we review recent advances and challenges in our understanding of how different mutational subsets of WNT tumour suppressor genes link to distinct cancer types, clinical outcomes and treatment strategies.

Serrated lesions of the colon and rectum: Emergent epidemiological data and molecular pathways

In 2010, serrated polyps (SP) of the colon have been included in the WHO classification of digestive tumors. Since then a large corpus of evidence focusing on these lesions are available in the literature. This review aims to analyze the present data on the epidemiological and molecular aspects of SP. Hyperplastic polyps (HPs) are the most common subtype of SP (70–90%), with a minimal or null risk of malignant transformation, contrarily to sessile serrated lesions (SSLs) and traditional serrated adenomas (TSAs), which represent 10–20% and 1% of adenomas, respectively. The malignant transformation, when occurs, is supported by a specific genetic pathway, known as the serrated-neoplasia pathway. The time needed for malignant transformation is not known, but it may occur rapidly in some lesions. Current evidence suggests that a detection rate of SP ≥15% should be expected in a population undergoing screening colonoscopy. There are no differences between primary colonoscopies and those carried out after positive occult fecal blood tests, as this screening test fails to identify SP, which rarely bleed. Genetic similarities between SP and interval cancers suggest that these cancers could arise from missed SP. Hence, the detection rate of serrated-lesions should be evaluated as a quality indicator of colonoscopy. There is a lack of high-quality longitudinal studies analyzing the long-term risk of developing colorectal cancer (CRC), as well as the cancer risk factors and molecular tissue biomarkers. Further studies are needed to define an evidence-based surveillance program after the removal of SP, which is currently suggested based on experts’ opinions.

A Focused Review on Advances in Risk Stratification of Malignant Polyps

Colorectal cancer is the third most common cancer in both men and women in the United States, with most cases arising from precursor adenomatous polyps. Colorectal malignant polyps are defined as cancerous polyps that consist of tumor cells invading through the muscularis mucosae into the underlying submucosa (pT1 tumor). It has been reported that approximately 0.5-8.3% of colorectal polyps are malignant polyps, and the potential for lymph node metastasis in these polyps ranges from 8.5% to 16.1%. Due to their clinical significance, recognition of malignant polyps is critical for clinical teams to make treatment decisions and establish appropriate surveillance schedules after local excision of the polyps. There is a rapidly developing interest in malignant polyps within the literature as a result of an increasing number of identifiable adverse histologic features and recent advancements in endoscopic treatment techniques. The purpose of this paper is to have a focused review of the recent histopathologic literature of malignant polyps.

Clinicopathologic and Molecular Characteristics of Familial Adenomatous Polyposis-associated Traditional Serrated Adenoma

Colorectal carcinogenesis in familial adenomatous polyposis (FAP) follows a conventional adenoma-carcinoma sequence. However, previous studies have also reported the occurrence of traditional serrated adenomas (TSAs) in patients with FAP. In the present study, we analyzed the clinicopathologic and molecular features of 37 TSAs from 21 FAP patients. Histologically, the majority of FAP-associated TSAs showed typical cytology and slit-like serration; however, ectopic crypt formation was infrequent. Next-generation sequencing and Sanger sequencing identified KRAS and BRAF V600E mutations in 18 (49%) and 14 (38%) TSAs, respectively. Somatic APC mutations were detected in 26 lesions (84% of analyzed cases). Three lesions had BRAF non-V600E mutations, and 2 of them had a concurrent KRAS mutation. Seven TSAs (19%) were associated with a precursor polyp, 6 with a hyperplastic polyp, and 1 with a sessile serrated lesion, and all of them showed the BRAF V600E mutation. Additional sequencing analysis of 4 TSAs with a precursor polyp showed that the BRAF V600E mutation was shared between the TSA and precursor components, but APC mutations were exclusive to the TSA component in all the analyzed lesions. None of the lesions showed the high CpG island methylation phenotype. These results indicate that FAP-associated TSAs frequently have KRAS or BRAF mutations, similar to sporadic cases, and second-hit somatic APC mutations are commonly involved in their tumorigenesis as in other FAP-associated tumors. Although progression to adenocarcinoma is likely rare, tumorigenesis via the serrated pathway occurs in patients with FAP.

BRAFV600E drives dedifferentiation in small intestinal and colonic organoids and cooperates with mutant p53 and Apc loss in transformation

BRAF^V600E confers poor prognosis and is associated with a distinct subtype of colorectal cancer (CRC). Little is known, however, about the genetic events driving the initiation and progression of BRAF^V600E mutant CRCs. Recent genetic analyses of CRCs indicate that BRAF^V600E often coexists with alterations in the WNT- and p53 pathways, but their cooperation remains ill-defined. Therefore, we systematically compared small and large intestinal organoids from mice harboring conditional Braf^floxV600E, Trp53^LSL-R172H, and/or Apc^flox/flox alleles. Using these isogenic models, we observe tissue-specific differences toward sudden BRAF^V600E expression, which can be attributed to different ERK-pathway ground states in small and large intestinal crypts. BRAF^V600E alone causes transient proliferation and suppresses epithelial organization, followed by organoid disintegration. Moreover, BRAF^V600E induces a fetal-like dedifferentiation transcriptional program in colonic organoids, which resembles human BRAF^V600E-driven CRC. Co-expression of p53^R172H delays organoid disintegration, confers anchorage-independent growth, and induces invasive properties. Interestingly, p53^R172H cooperates with BRAF^V600E to modulate the abundance of transcripts linked to carcinogenesis, in particular within colonic organoids. Remarkably, WNT-pathway activation by Apc deletion fully protects organoids against BRAF^V600E-induced disintegration and confers growth/niche factor independence. Still, Apc-deficient BRAF^V600E-mutant organoids remain sensitive toward the MEK inhibitor trametinib, albeit p53^R172H confers partial resistance against this clinically relevant compound. In summary, our systematic comparison of the response of small and large intestinal organoids to oncogenic alterations suggests colonic organoids to be better suited to model the human situation. In addition, our work on BRAF-, p53-, and WNT-pathway mutations provides new insights into their cooperation and for the design of targeted therapies.

Evolving pathologic concepts of serrated lesions of the colorectum

Here, we provide an up-to-date review of the histopathology and molecular pathology of serrated colorectal lesions. First, we introduce the updated contents of the 2019 World Health Organization classification for serrated lesions. The sessile serrated lesion (SSL) is a new diagnostic terminology that replaces sessile serrated adenoma and sessile serrated polyp. The diagnostic criteria for SSL were revised to require only one unequivocal distorted serrated crypt, which is sufficient for diagnosis. Unclassified serrated adenomas have been included as a new category of serrated lesions. Second, we review ongoing issues concerning the morphology of serrated lesions. Minor morphologic variants with distinct molecular features were recently defined, including serrated tubulovillous adenoma, mucin-rich variant of traditional serrated adenoma (TSA), and superficially serrated adenoma. In addition to intestinal dysplasia and serrated dysplasia, minimal deviation dysplasia and not otherwise specified dysplasia were newly suggested as dysplasia subtypes of SSLs. Third, we summarize the molecular features of serrated lesions. The critical determinant of CpG island methylation development in SSLs is patient age. Interestingly, there may be ethnic differences in BRAF/KRAS mutation frequencies in SSLs. The molecular pathogenesis of TSAs is divided into KRAS and BRAF mutation pathways. SSLs with MLH1 methylation can progress into favorable prognostic microsatellite instability-positive (MSI+)/CpG island methylator phenotype-positive (CIMP+) carcinomas, whereas MLH1-unmethylated SSLs and BRAF-mutated TSAs can be precursors of poor-prognostic MSI-/CIMP+ carcinomas. Finally, based on our recent data, we propose an algorithm for stratifying risk subgroups of non-dysplastic SSLs.

Correlations of morphology and molecular alterations in traditional serrated adenoma

Traditional serrated adenoma was first reported by Longacre and Fenoglio-Presier in 1990. Their initial study described main features of this lesion, but the consensus diagnostic criteria were not widely adopted until recently. Traditional serrated adenoma presents with grossly protuberant configuration and pinecone-like appearance upon endoscopy. Histologically, it is characterized by ectopic crypt formation, slit-like serration, eosinophilic cytoplasm and pencillate nuclei. Although much is now known about the morphology and molecular changes, the mechanisms underlying the morphological alterations are still not fully understood. Furthermore, the origin of traditional serrated adenoma is not completely known. We review recent studies of the traditional serrated adenoma and provide an overview on current understanding of this rare entity.

APC Mutation Marks an Aggressive Subtype of BRAF Mutant Colorectal Cancers

BACKGROUND

WNT activation is a hallmark of colorectal cancer. BRAF mutation is present in 15% of colorectal cancers, and the role of mutations in WNT signaling regulators in this context is unclear. Here, we evaluate the mutational landscape of WNT signaling regulators in BRAF mutant cancers.

METHODS

we performed exome-sequencing on 24 BRAF mutant colorectal cancers and analyzed these data in combination with 175 publicly available BRAF mutant colorectal cancer exomes. We assessed the somatic mutational landscape of WNT signaling regulators, and performed hotspot and driver mutation analyses to identify potential drivers of WNT signaling. The effects of Apc and Braf mutation were modelled, in vivo, using the Apcmin/+ and BrafV637/Villin-CreERT2/+ mouse, respectively.

RESULTS

RNF43 was the most frequently mutated WNT signaling regulator (41%). Mutations in the beta-catenin destruction complex occurred in 48% of cancers. Hotspot analyses identified potential cancer driver genes in the WNT signaling cascade, including MEN1, GNG12 and WNT16. Truncating APC mutation was identified in 20.8% of cancers. Truncating APC mutation was associated with early age at diagnosis (p < 2 × 10-5), advanced stage (p < 0.01), and poor survival (p = 0.026). Apcmin/+/BrafV637 animals had more numerous and larger SI and colonic lesions (p < 0.0001 and p < 0.05, respectively), and a markedly reduced survival (median survival: 3.2 months, p = 8.8 × 10-21), compared to animals with Apc or Braf mutation alone.

CONCLUSIONS

the WNT signaling axis is frequently mutated in BRAF mutant colorectal cancers. WNT16 and MEN1 may be novel drivers of aberrant WNT signaling in colorectal cancer. Co-mutation of BRAF and APC generates an extremely aggressive neoplastic phenotype that is associated with poor patient outcome.

Clinicopathological and molecular correlations in traditional serrated adenoma

BACKGROUND

Traditional serrated adenoma (TSA) is the least common type of colorectal serrated polyp, which exhibits considerable morphological and molecular diversity.

METHODS

We examined the spectra of alterations in MAPK and WNT pathway genes and their relationship with clinicopathological features in 128 TSAs.

RESULTS

Sequencing analyses identified BRAF V600E, BRAF non-V600E, KRAS, and NRAS mutations in 77, 3, 45, and 1 lesion, respectively. Collectively, 124 lesions (97%) had mutations in MAPK pathway genes. Alterations in WNT pathway genes were identified in 107 lesions (84%), including RSPO fusions/overexpression, RNF43 mutations, ZNRF3 mutations, APC mutations, and CTNNB1 mutations in 47, 45, 2, 13, and 2 lesions, respectively. Ten lesions (8%) harbored GNAS mutations. There was significant interdependence between the altered MAPK and WNT pathway genes. RSPO fusions/overexpression was significantly associated with KRAS mutations (31/47, 66%), whereas most RNF43 mutations coexisted with the BRAF V600E mutation (40/45, 89%). Histologically, extensive slit-like serration was more common in lesions with the BRAF V600E mutation (71%) and those with RNF43 mutations (87%). Prominent ectopic crypt formation was more prevalent in lesions with RSPO fusions/overexpression (58%) and those with GNAS mutations (100%).

CONCLUSIONS

Our observations indicate that TSAs mostly harbor various combinations of concurrent WNT and MAPK gene alterations. The associations between genetic and morphological features suggest that the histological diversity of TSA reflects the underlying molecular heterogeneity.

Cancer cell niche factors secreted from cancer-associated fibroblast by loss of H3K27me3

OBJECTIVE

Cancer-associated fibroblasts (CAFs), a major component of cancer stroma, can confer aggressive properties to cancer cells by secreting multiple factors. Their phenotypes are stably maintained, but the mechanisms are not fully understood. We aimed to show the critical role of epigenetic changes in CAFs in maintaining their tumour-promoting capacity and to show the validity of the epigenomic approach in identifying therapeutic targets from CAFs to starve cancer cells.

DESIGN

Twelve pairs of primary gastric CAFs and their corresponding non-CAFs (NCAFs) were established from surgical specimens. Genome-wide DNA methylation and H3K27me3 analyses were conducted by BeadArray 450K and ChIP-on-Chip, respectively. Functions of potential a therapeutic target were analysed by inhibiting it, and prognostic impact was assessed in a database.

RESULTS

CAFs had diverse and distinct DNA methylation and H3K27me3 patterns compared with NCAFs. Loss of H3K27me3, but not DNA methylation, in CAFs was enriched for genes involved in stem cell niche, cell growth, tissue development and stromal-epithelial interactions, such as WNT5A, GREM1, NOG and IGF2. Among these, we revealed that WNT5A, which had been considered to be derived from cancer cells, was highly expressed in cancer stromal fibroblasts, and was associated with poor prognosis. Inhibition of secreted WNT5A from CAFs suppressed cancer cell growth and migration.

CONCLUSIONS

H3K27me3 plays a crucial role in defining tumour-promoting capacities of CAFs, and multiple stem cell niche factors were secreted from CAFs due to loss of H3K27me3. The validity of the epigenetic approach to uncover therapeutic targets for cancer-starving therapy was demonstrated.

Correlation of molecular and morphological features of appendiceal epithelial neoplasms

AIMS

The aims of this study were to identify the genetic features of appendiceal epithelial neoplasms and correlate the genetic features with morphology.

METHODS AND RESULTS

We analysed the genetic features of a series of 47 appendiceal epithelial neoplasms of various morphologies by using targeted next-generation sequencing of 11 genes commonly mutated in gastrointestinal neoplasms. Seven of nine serrated polyps harboured BRAF mutations, which are rare in other types of appendiceal tumours. Most cases of low-grade appendiceal mucinous neoplasms (LAMNs) exhibited GNAS and KRAS mutations. LAMNs with a coexisting serrated polyp were all KRAS mutated. Four LAMNs with mutations in the Wnt/β-catenin pathway, either through inactivating mutations in APC or RNF43 or activating mutations in CTNNB1, had focal proliferation of mucin-poor low-grade tumour cells, reminiscent of colorectal adenomas. Mutations in the Wnt/β-catenin pathway were also identified in high-grade appendiceal mucinous neoplasms, suggesting that Wnt/β-catenin pathway activation is the driving force for the progression of LAMN to a higher-grade lesion. Adenomatous polyps of the appendix frequently had APC, KRAS and TP53 mutations and were morphologically and molecularly similar to adenomatous polyps of the colorectum.

CONCLUSIONS

Our results indicate a close association between morphology and genetic events in appendiceal neoplasms and suggest a phylogenetic relationship between different entities.

Traditional serrated adenoma: an overview of pathology and emphasis on molecular pathogenesis

Objective

To provide an overview of the pathology and molecular pathogenesis of traditional serrated adenomas (TSA).

Design

Describe the morphology and molecules that play a role in their pathogenesis.

Results

These exuberant polypoid lesions are typified by tall cells with deeply eosinophilic cytoplasm, elongated nuclei bearing delicate chromatin, ectopic crypt foci, deep clefting of the lining mucosa and an overall resemblance to small bowel mucosa.

Broadly, TSAs arise via three mechanisms. They may be BRAF mutated and CpG island methylator phenotype (CIMP)-high: right sided, mediated through a microvesicular hyperplastic polyp or a sessile serrated adenoma, may also have RNF43 mutations and result in microsatellite stable (MSS) colorectal cancers (CRC). The second pathway that is mutually exclusive of the first is mediated through KRAS mutation with CIMP-low TSAs. These are left-sided TSAs, are not associated with another serrated polyp and result in MSS CRC. These TSAs also have RSPO3, RNF43 and p53 mutations together with aberrant nuclear localisation of β-catenin. Third, there is a smaller group of TSAs that are BRAF and KRAS wild type and arise by as yet unknown molecular events. All TSAs show retention of mismatch repair proteins.

Conclusion

These are characteristic unusual polyps with a complex molecular landscape.

The Molecular Hallmarks of the Serrated Pathway in Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. It includes different subtypes that differ in their clinical and prognostic features. In the past decade, in addition to the conventional adenoma-carcinoma model, an alternative multistep mechanism of carcinogenesis, namely the “serrated pathway”, has been described. Approximately, 15 to 30% of all CRCs arise from neoplastic serrated polyps, a heterogeneous group of lesions that are histologically classified into three morphologic categories: hyperplastic polyps, sessile serrated adenomas/polyps, and the traditional serrated adenomas/polyps. Serrated polyps are characterized by genetic (BRAF or KRAS mutations) and epigenetic (CpG island methylator phenotype (CIMP)) alterations that cooperate to initiate and drive malignant transformation from normal colon mucosa to polyps, and then to CRC. The high heterogeneity of the serrated lesions renders their diagnostic and pathological interpretation difficult. Hence, novel genetic and epigenetic biomarkers are required for better classification and management of CRCs. To date, several molecular alterations have been associated with the serrated polyp-CRC sequence. In addition, the gut microbiota is emerging as a contributor to/modulator of the serrated pathway. This review summarizes the state of the art of the genetic, epigenetic and microbiota signatures associated with serrated CRCs, together with their clinical implications.

EIF3E-RSPO2 and PIEZO1-RSPO2 fusions in colorectal traditional serrated adenoma

AIMS

Traditional serrated adenoma (TSA) is an uncommon type of colorectal serrated polyp. RSPO fusions, which potentiate WNT signalling, are common and characteristic genetic alterations in TSA. The aim of this study was to further characterise the prevalence and variation of RSPO fusions in TSA.

METHODS AND RESULTS

Quantitative polymerase chain reaction (PCR) analysis of 99 TSAs revealed overexpression of RSPO2 and RSPO3 in six and 29 lesions, respectively. Reverse transcription PCR identified previously reported PTPRK-RSPO3 fusion transcripts in all 29 TSAs with RSPO3 overexpression, confirming that PTPRK-RSPO3 is the predominant RSPO fusion in TSAs. Among the six lesions with RSPO2 overexpression, two overexpressed full-length RSPO2. An EIF3E-RSPO2 fusion, which is a known recurrent RSPO fusion in colorectal cancer, was detected in three lesions. In addition, rapid amplification of cDNA ends identified a novel PIEZO1-RSPO2 fusion in one TSA. All of the four TSAs with RSPO2 fusions concurrently had KRAS mutations and showed the classic histological features.

CONCLUSIONS

The present study identified EIF3E-RSPO2 and PIEZO1-RSPO2 in TSAs. Our observations expand the spectrum of RSPO fusions in TSAs, and suggest that TSAs are precursors of colorectal cancers with these RSPO2 fusions.

Clinicopathological factors associated with BRAF-V600E mutation in colorectal serrated adenomas

Serrated adenomas are genetically heterogeneous, and the histological classification into sessile serrated (SSA) adenoma and traditional serrated adenoma (TSA) does not reflect the molecular landscape. The objective of this study was to assess clinical or pathological factors associated with BRAF-V600E mutation in serrated adenomas. Systematic review and meta-analysis was performed by searching electronic databases from January 2011 to January 2019 for studies assessing the association of BRAF-V600E mutation with clinical or pathological features of serrated adenomas. Odds ratio (OR) was calculated for each factor; a P-value <0.05 was considered significant. Forty studies assessing 3511 serrated adenomas (2375 SSAs and 1136 TSAs) were included. BRAF-V600E mutation was significantly associated with proximal localisation (OR = 2.71; P < 0.00001) and CIMP-H status (OR = 4.81; P < 0.0001) in both SSA and TSA, with polyp size <10 mm (OR = 0.41; P = 0.02) in TSA, and with endoscopic pit pattern II-O (OR = 13.11; P < 0.00001) and expression of MUC5A5 (OR = 4.43; P = 0.003) and MUC6 (OR = 2.28; P < 0.05) in SSA. Conversely, BRAF mutation was not associated with age <70 years (OR = 1.63; P = 0.34), age <60 years (OR = 0.86; P = 0.79), female sex (OR = 0.77; P = 0.12), flat morphology (OR = 1.52; P = 0.16), presence of any dysplasia (OR = 1.01; P = 0.59), serrated dysplasia (OR = 1.23; P = 0.72) and invasive cancer (OR = 0.67; P = 0.32), nuclear β-catenin expression (OR = 0.73; P = 0.21) and p53 overexpression (OR = 1.24; P = 0.82). In conclusion, BRAF-V600E mutation is associated with proximal localisation and CIMP-H status in both SSA and TSA, with size <10 mm only in TSA, and with expression of MUC5A5 and MUC6 and endoscopic pit pattern II-O at least in SSA. In serrated adenomas, BRAF-V600E mutation does not seem to be associated with age and sex, with the prevalence of dysplasia and cancer and with the morphology of the dysplastic component.