Characterisation of a subtype of colorectal cancer combining features of the suppressor and mild mutator pathways

Microsatellite instability evaluation by a novel PCR-based 8-loci test kit in colorectal cancer

Microsatellite instability (MSI) assessment is strongly recommended for colorectal cancer patients, as MSI status is crucial in determining optimal treatment and predicting prognosis. This study evaluated the reliability and accuracy of a novel polymerase chain reaction (PCR)-based 8-loci MSI test kit, a rapid test kit designed to detect MSI, by comparing its performance with immunohistochemistry (IHC) and the National Cancer Institute (NCI) 2B3D Panel. MSI status was determined in 186 formalin-fixed paraffin-embedded (FFPE) colorectal cancer tissue samples with known mismatch repair (MMR) status by IHC using the novel PCR-based 8-loci MSI test kit. Additionally, the consistency between the NCI 2B3D Panel and the novel PCR-based 8-loci panel was compared using 69 FFPE tumor tissues paired with adjacent non-cancerous tissue. The novel PCR-based 8-loci MSI test kit and IHC demonstrated high concordance (overall agreement: 97.8%). However, four samples displayed discordant results, exhibiting MMR deficiency using IHC and microsatellite stability using the novel PCR-based 8-loci MSI test kit. Of the 69 samples reanalyzed using the NCI 2B3D Panel, high concordance with the novel PCR-based 8-loci MSI test kit was observed in 67 of 69 cases (overall agreement: 97.1%). The novel PCR-based 8-loci MSI test kit is a rapid and reliable tool for accurately detecting MSI status in colorectal cancer.

BAT26 Only Microsatellite Instability with High Tumor Mutation Burden—A Rare Entity Associated with PTEN Protein Loss and High PD-L1 Expression

Detecting microsatellite instability (MSI) in advanced cancers is crucial for clinical decision-making, as it helps in identifying patients with differential treatment responses and prognoses. BAT26 is a highly sensitive MSI marker that defines the mismatch repair (MMR) status with high sensitivity and specificity. However, isolated BAT26-only instability is rare and has not been previously reported. Of the 6476 cases tested using pentaplex MSI polymerase chain reaction, we identified two BAT26-only instability cases (0.03%) in this study. The case #1 patient was diagnosed with endometrial adenocarcinoma without MMR germline mutations. The endometrial tumor showed BAT26-only instability, partial loss of MLH1/PMS2 protein expression, and a high programmed cell death ligand 1 (PD-L1) combined positive score (CPS = 8). The tumor exhibited a somatic phosphatase and tensin homolog (PTEN) R303P missense mutation and loss of the PTEN protein. On a comprehensive cancer panel sequencing with ≥500 genes, the tumor showed an MSI score of 11.38% and high tumor mutation burden (TMB) (19.5 mt/mb). The case #2 patient was diagnosed with colorectal carcinoma with proficient MMR and PTEN protein loss without PTEN alteration, as well as a high PD-L1 CPS (CPS = 10). A pathogenic KRAS A146T mutation was detected with an MSI score of 3.36% and high TMB (13 mt/mb). In conclusion, BAT26-only instability is very rare and associated with PTEN protein loss, high TMB, and a high PD-L1 score. Our results suggest that patients with BAT26-only instability may show good responses to immunotherapy.

Immunogenic characteristics of microsatellite instability-low esophagogastric junction adenocarcinoma based on clinicopathological, molecular, immunological and survival analyses

Microsatellite instability (MSI) is categorized by mutation frequency: high MSI (MSI-H), low MSI (MSI-L) and microsatellite stable (MSS). MSI-H tumors have a distinct immunogenic phenotype, with immunotherapies using checkpoint inhibitors already approved for the treatment of MSI-H gastroesophageal adenocarcinoma (GEA); this is not observed for MSI-L or MSS. Here, we tested the hypothesis that MSI-L tumors are also a distinct phenotype and potentially immunogenic. MSI-PCR assays (BAT25, BAT26, BAT40, D2S123, D5S346 and D17S250) were performed on 363 Epstein-Barr virus-negative, surgically resected esophagogastric junction (EGJ) adenocarcinoma samples. Tumors were characterized as MSI-H (≥2 markers), MSI-L (1 marker) or MSS (0 markers). CD8+ cell counts, PD-L1 and HER2 expression levels, TP53 mutations, epigenetic alterations and prognostic significance were also examined. All pathological and molecular experiments were conducted using serial, whole-tumor sections of chemo-naïve surgical specimens. MSI-H and MSI-L were assigned to 28 (7.7%) and 24 (6.6%) cases, respectively. Compared to MSS cases, MSI-L cases had significantly higher intratumoral CD8+ cell infiltration (P = .048) and favorable EGJ cancer-specific survival (multivariate hazard ratio = 0.35, 95% CI, 0.12-0.82; P = .012). MSI-L tumors were also significantly associated with TP53-truncating mutations as compared to MSI-H (P = .009) and MSS (P = .012) cases, and this trend was also observed in GEA data from The Cancer Genome Atlas (TCGA). Indel mutational burden among TCGA MSI-L tumors was significantly higher than that of MSS tumors (P = .016). These results suggest that MSI-L tumors may have a distinct tumor phenotype and be potentially immunogenic in EGJ adenocarcinoma.

Low level of microsatellite instability correlates with short disease-free survival of gastric cancer patients undergoing neoadjuvant chemotherapy

Limited studies have been reported about the function of low level of microsatellite instability (MSI-L) in cancer. The aim of our study is to unveil the prognostic role of MSI-L in gastric cancer (GC). One hundred nine patients with locally advanced GC (T3-4a, N+, M0) who underwent neoadjuvant chemotherapy plus gastrectomy with extended (D2) lymph node dissection were collected. Clinicopathological characteristics, tumour regression score, disease-free survival (DFS), and overall survival (OS) were analysed and correlated with the MSI status. The MSI status of 96 patients was identified (7 (7.3%) with MSI-H, 12 (12.5%) with MSI-L, and 77 (80.2%) with MSS). MSI-L was significantly correlated with perineural invasion (P = 0.009) and decreased MUC5AC expression (P = 0.042). Poor response to neoadjuvant chemotherapy in MSI-L patients (83.3% assessed as poor response) was observed (P = 0.501). Compared with patients with MSS tumours, patients with MSI-L tumours showed poor DFS (P = 0.018) with a hazard ratio (HR) of 2.839 (95% CI 1.131-7.124, P = 0.026) from multivariable cox regression analysis. However, this was not associated with OS (P = 0.063). MSI-L is an independent poor prognostic biomarker for the locally advanced gastric cancer treated with neoadjuvant chemotherapy. Further studies with larger sample sizes are needed for validation.

Evaluation of a Fully Automated Idylla Test System for Microsatellite Instability in Colorectal Cancer

BACKGROUND

Microsatellite instability (MSI) is a phenotype commonly observed in colorectal cancer, and is caused by a deficient mismatch repair system. Determining MSI status greatly aids tumor prognosis and treatment plans in colorectal cancer, and plays a critical role in recent United States Food and Drug Administration-approved immunotherapies. As recognition of its importance grows, MSI has been identified in more types of cancers, underscoring the importance of accurate assays for determining MSI status in tumor cells. Currently, tumor MSI status is detected via polymerase chain reaction-based methods or immunohistochemistry.

MATERIALS AND METHODS

In this study, we tested a new, fully automated MSI detection system (Idylla MSI detection kit) released by Biocartis. We evaluated 42 formalin-fixed paraffin-embedded tumor tissues, which were clinically tested for MSI status using the polymerase chain reaction or immunohistochemistry method, with the Idylla MSI detection system.

RESULTS

The Idylla MSI detection system showed an overall 97.62% concordance rate with previously used methods. Moreover, this fully automated system requires less than 5 minutes "hands on" preparation time and 150 minutes total run time per sample.

CONCLUSION

The Biocartis Idylla MSI kit proves a powerful tool to accurately detect MSI status in tumor cells in a rapid and almost labor-free manner.

ARID1A loss impairs enhancer-mediated gene regulation and drives colon cancer in mice

Genes encoding subunits of SWI/SNF (BAF) chromatin-remodeling complexes are collectively mutated in ∼20% of all human cancers. Although ARID1A is the most frequent target of mutations, the mechanism by which its inactivation promotes tumorigenesis is unclear. Here we demonstrate that Arid1a functions as a tumor suppressor in the mouse colon, but not the small intestine, and that invasive ARID1A-deficient adenocarcinomas resemble human colorectal cancer (CRC). These tumors lack deregulation of APC/β-catenin signaling components, which are crucial gatekeepers in common forms of intestinal cancer. We find that ARID1A normally targets SWI/SNF complexes to enhancers, where they function in coordination with transcription factors to facilitate gene activation. ARID1B preserves SWI/SNF function in ARID1A-deficient cells, but defects in SWI/SNF targeting and control of enhancer activity cause extensive dysregulation of gene expression. These findings represent an advance in colon cancer modeling and implicate enhancer-mediated gene regulation as a principal tumor-suppressor function of ARID1A.

β-Catenin Expression Negatively Correlates with WIF1 and Predicts Poor Clinical Outcomes in Patients with Cervical Cancer

Aberrant activation of the canonical Wnt pathway plays a significant role in cervical cancer (CC). However, limited data show the correlation between the cancer clinicopathological characteristics and the key molecules such as β-catenin and Wnt inhibitory factor 1 (WIF1). In this study, β-catenin and WIF1 expression were analyzed by immunohistochemistry for 196 patients with CC, 39 with cervical intraepithelial neoplasia (CIN), and 41 with normal cervical epithelium (NCE). Significant overexpression of β-catenin was detected in CC (67.9%) when compared to CIN (43.6%) or NCE (34.1%), p < 0.01, while low WIF1 expression was detected in CC (24.0%) when compared to CIN (59.0%) or NCE (58.5%), p < 0.001. Negative correlation was shown between β-catenin and WIF1 expression (r = −0.637, p < 0.001). In addition, multivariate analysis revealed that both lymph node metastasis and β-catenin expression were the independent prognostic factors not only for disease-free survival (HR = 5.029, p < 0.001; HR = 2.588, p = 0.035, resp.), but also for overall survival (HR = 5.058, p < 0.001; HR = 2.873, p = 0.031, resp.). Our findings indicate that, besides lymph node metastasis, β-catenin expression may also be a poor prognostic factor for CC while WIF1 could be a potential drug target for treatment of advanced CC.

Finding sessile serrated adenomas: is it possible to identify them during conventional colonoscopy?

BACKGROUND AND AIM

Proximal colorectal cancer may arise from sessile serrated adenomas (SSAs). Recognition of these lesions during colonoscopy can optimize the endoscopic approach. We aimed to identify specific endoscopic features of SSA with conventional colonoscopy.

METHODS

Patients undergoing screening colonoscopies from January 2011 to September 2012, in whom colonic polyps were found, were prospectively included in our study. Polyp morphology, location, polyp pit pattern (Kudo classification), and other previously reported features of SSA were evaluated. Histological examination was conducted independently by two pathologists. Multivariate analysis was performed to identify independent predictors of SSA.

RESULTS

A total of 272 patients were included, and 440 polyps were evaluated (1.6 polyps per patient). Thirty-four polyps (8%) were SSA, 135 (31%) hyperplastic, and 249 (56%) adenomas. The most prevalent endoscopic features of SSA were right-side location (94%), type II Kudo pit pattern (91%), mucus cap (41%), flat morphology (29%) and red-colored surface (26%). Multivariate analysis revealed that flat morphology (p = 0.002, OR = 3.81 CI 1.53-9.09), red-colored surface (p < 0.001, OR = 12.97 CI 4.43-37.69), right-side location (p < 0.001, OR = 22.21 CI 5.09-135.94) and mucus cap (p < 0.001, OR 8.77 CI 3.76-20.44) were independent predictors of SSA.

CONCLUSION

We were able to identify specific features of SSA during conventional colonoscopy, which may help to identify, and therefore to optimize the endoscopic approach of these lesions.

Sporadic early-onset colorectal cancer is a specific sub-type of cancer: a morphological, molecular and genetics study

Sporadic early onset colorectal carcinoma (EOCRC) which has by definition no identified hereditary predisposition is a growing problem that remains poorly understood. Molecular analysis could improve identification of distinct sub-types of colorectal cancers (CRC) with therapeutic implications and thus can help establish that sporadic EOCRC is a distinct entity. From 954 patients resected for CRC at our institution, 98 patients were selected. Patients aged 45–60 years were excluded to help define “young” and “old” groups. Thirty-nine cases of sporadic EOCRC (patients≤45 years with microsatellite stable tumors) were compared to both microsatellite stable tumors from older patients (36 cases, patients>60 years) and to groups of patients with microsatellite instability. Each group was tested for TP53, KRAS, BRAF, PIK3CA mutations and the presence of a methylator phenotype. Gene expression profiles were also used for pathway analysis. Compared to microsatellite stable CRC from old patients, sporadic EOCRC were characterized by distal location, frequent synchronous metastases and infrequent synchronous adenomas but did not have specific morphological characteristics. A familial history of CRC was more common in sporadic EOCRC patients despite a lack of identified hereditary conditions (p = 0.013). Genetic studies also showed the absence of BRAF mutations (p = 0.022) and the methylator phenotype (p = 0.005) in sporadic EOCRC compared to older patients. Gene expression analysis implicated key pathways such as Wnt/beta catenin, MAP Kinase, growth factor signaling (EGFR, HGF, PDGF) and the TNFR1 pathway in sporadic EOCRC. Wnt/beta catenin signaling activation was confirmed by aberrant nuclear beta catenin immunostaining (p = 0.01). This study strongly suggests that sporadic EOCRC is a distinct clinico-molecular entity presenting as a distal and aggressive disease associated with chromosome instability. Furthermore, several signaling pathways including the TNFR1 pathway have been identified as potential biomarkers for both the diagnosis and treatment of this disease.

A single nucleotide polymorphism in fibronectin 1 determines tumor shape in colorectal cancer

Depressed and flat surface lesions are not easy to identify with routine colonoscopies during screening for colorectal cancer (CRC). Identifying clinically relevant genes that influence tumor shape could be useful when screening for the presence of depressed lesions. Total RNA was extracted from tumor cells collected by laser microdissection from the primary lesions of 146 CRC cases. Microarray analysis was performed to identify genes that were differentially expressed between depressed and elevated tumors. Single nucleotide polymorphism (SNP) analysis of genomic DNA from the peripheral blood of 67 CRC patients was then used to associate polymorphisms with the occurrence of depressed tumors. Microarray analysis revealed significantly higher expression of the fibronectin 1 (FN1) gene in 129 depressed-type tumors and lesions compared to 17 elevated-type tumors. FN1-abundant CRC tumors were large with a significantly higher incidence of lymphatic permeation. SNP analysis indicated that 44 tumors with a GG genotype at SNP rs6707530 showed significantly higher FN1 expression than did 23 tumors with GT/TT genotypes (p<0.05). The product of the FN1 gene (located at 2q34) is involved in cell adhesion, migration and metastasis in mesenchymal tumors. Abundant expression of FN1 may allow cancer cells to invade deeper layers, which would eventually define tumor shape. Identification of this SNP in blood samples may facilitate disease diagnosis and allow prediction of the presence of depressed tumors in the colorectal epithelium before a colon fiberscope examination.

Microsatellite instability testing in Korean patients with colorectal cancer

Microsatellite instability (MSI) testing is useful for identifying patients with hereditary nonpolyposis colorectal cancer and detecting sporadic colorectal cancer that develops through replication error pathways. A pentaplex panel is recommended by the National Cancer Institute for MSI testing, but simplified mononucleotide panels and immunohistochemistry of mismatch repair proteins are widely employed for convenience. This study was to evaluate the MSI status of colorectal cancer in Korean patients. This study included 1,435 patients with colorectal adenocarcinoma subjected to surgical resection. The pentaplex Bethesda panel was used for MSI testing. Seventy nine (5.5 %) carcinomas were classified as MSI-high (MSI-H) and 95 (6.6 %) as MSI-low (MSI-L). BAT-26 and BAT-25 were unstable in 73 and 75 of 79 MSI-H carcinomas, respectively. With the panel comprising these 2 mononucleotide markers, 72 carcinomas were diagnosed as MSI-H, compared to the Bethesda panel data (72/79, 91.1 %). In contrast, BAT-26 or BAT-25 were unstable in only 7 (7.4 %) of the 95 MSI-L tumors. In the panel with 2 dinucleotide markers, D17250 linked to p53 and D2S123 to hMSH2, detection rates were 89.9 % (71/79) for MSI-H and 80.0 % (76/95) for MSI-L carcinomas, compared to the Bethesda panel. Moreover, we compared the frequency of MSI tumor in our patients with those reported previously from Western countries. In conclusion, the frequency of MSI-H appears lower in colorectal cancer patients in Korea. A simplified panel for MSI testing with BAT-26 and BAT-25 seems not effective for the accurate evaluation of MSI status, particularly in MSI-L colorectal carcinomas, in our patients.

KRAS gene mutations are more common in colorectal villous adenomas and in situ carcinomas than in carcinomas

We have evaluated the frequency of KRAS gene mutations during the critical transition from villous adenoma to colorectal carcinoma to assess whether the adenomas contain a KRAS mutation more frequently than carcinomas. We analyzed sporadic villous and tubulovillous adenomas, in situ carcinomas, and primary colorectal carcinomas from multiple patients. The cancers were further evaluated for mucinous status and microsatellite instability. Standard PCR molecular techniques were used for KRAS and microsatellite analyses. A KRAS mutation was found in 61.9% of 134 adenomas, 67.8% of 84 in situ carcinomas, and just 31.6% of 171 carcinomas. Our study clearly demonstrates that tubulovillous and villous adenomas, as well as both the benign and malignant parts of in situ carcinomas, are statistically more likely to contain a somatic KRAS gene mutation than colorectal carcinomas. This difference is confined to the non-mucinous and the microsatellite stable tumors. Our data support the possibility that non-mucinous and microsatellite stable carcinomas with wild-type KRAS gene may have had a mutation in the KRAS gene during their earlier stages, with the mutation lost during further growth.

Management of stage II colon cancer - the use of molecular biomarkers for adjuvant therapy decision

BACKGROUND

There is uncertainty on the benefit of adjuvant chemotherapy in patients with stage II colorectal cancers. The aim of this study is to investigate the combined role of clinical, pathological and molecular parameters to identify those stage II patients who better benefit from adjuvant therapy.

METHODS

We examined 120 stage II colon cancer patients. Of these, 60 patients received adjuvant 5-FU chemotherapy after surgery and the other 60 did not receive therapy. Immunohistochemical (IHC) analyses were performed to evaluate the expressions of Thymidylate synthetase (TYMS), TP53 (p53), β-catenin (CTNNB1) and CD8. For TYMS, its mRNA expression levels were also investigated by real time qRT-PCR. The entire case study was characterized by the presence of a defect in the MMR (mismatch repair) system, the presence of the CpG island methylator phenotype (CIMP or CIMP-High) and for the V600E mutation in the BRAF gene. At the histo-pathological level, the depth of tumour invasion, lymphovascular invasion, invasion of large veins, host lymphocytic response and tumour border configuration were recorded.

RESULTS

The presence of the V600E mutation in the BRAF gene was a poor prognostic factor for disease free and overall survival (DFS; hazard ratio [HR], 2.57; 95% CI: 1.03 -6.37; p = 0.04 and OS; HR, 3.68; 95% CI: 1.43-9.47; p < 0.01 respectively), independently of 5-FU treatment. Adjuvant therapy significantly improved survival in patients with high TYMS levels (p = 0.04), while patients with low TYMS had a better outcome if treated by surgery alone (DFS; HR, 6.07; 95% CI, 0.82 to 44.89; p = 0.04). In patients with a defect in the MMR system (dMMR), 5-FU therapy was associated to reduced survival (DFS; HR, 37.98; 95% CI, 1.04 to 1381.31; p = 0.04), while it was beneficial for CIMP-High associated tumours (DFS; HR, 0.17; 95% CI, 0.02 to 1.13; p = 0.05).

CONCLUSIONS

Patients' characterization according to MMR status, CIMP phenotype and TYMS mRNA expression may provide a more tailored approach for adjuvant therapy in stage II colon cancer.

Associations of beta-catenin alterations and MSI screening status with expression of key cell cycle regulating proteins and survival from colorectal cancer

Background

Despite their pivotal roles in colorectal carcinogenesis, the interrelationship and prognostic significance of beta-catenin alterations and microsatellite instability (MSI) in colorectal cancer (CRC) needs to be further clarified. In this paper, we studied the associations between beta-catenin overexpression and MSI status with survival from CRC, and with expression of p21, p27, cyclin D1 and p53, in a large, prospective cohort study.

Methods

Immunohistochemical MSI-screening status and expression of p21, p27 and p53 was assessed in tissue microarrays with tumours from 557 cases of incident CRC in the Malmö Diet and Cancer Study. Chi Square and Spearman’s correlation tests were used to explore the associations between beta-catenin expression, MSI status, clinicopathological characteristics and investigative parameters. Kaplan-Meier analysis and Cox proportional hazards modelling were used to assess the relationship between beta-catenin overexpression, MSI status and cancer specific survival (CSS).

Results

Positive MSI screening status was significantly associated with older age, female sex, proximal tumour location, non-metastatic disease, and poor differentiation, and inversely associated with beta-catenin overexpression. Beta-catenin overexpression was significantly associated with distal tumour location, low T-stage and well-differentiated tumours. Patients with MSI tumours had a significantly prolonged CSS in the whole cohort, and in stage III-IV disease, also in multivariable analysis, but not in stage I-II disease. Beta-catenin overexpression was associated with a favourable prognosis in the full cohort and in patients with stage III-IV disease. Neither MSI nor beta-catenin status were predictive for response to adjuvant chemotherapy in curatively treated stage III patients. P53 and p27 expression was positively associated with beta-catenin overexpression and inversely associated with MSI. Cyclin D1 expression was positively associated with MSI and beta-catenin overexpression, and p21 expression was positively associated with MSI but not beta-catenin overexpression.

Conclusions

Findings from this large, prospective cohort study demonstrate that MSI screening status in colorectal cancer is an independent prognostic factor, but not in localized disease, and does not predict response to adjuvant chemotherapy. Beta-catenin overexpression was also associated with favourable outcome but not a treatment predictive factor. Associations of MSI and beta-catenin alterations with other investigative and clinicopathological factors were in line with the expected.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8778585058652609

Tumor-specific microsatellite instability: do distinct mechanisms underlie the MSI-L and EMAST phenotypes?

Microsatellite DNA sequences display allele length alterations or microsatellite instability (MSI) in tumor tissues, and MSI is used diagnostically for tumor detection and classification. We discuss the known types of tumor-specific MSI patterns and the relevant mechanisms underlying each pattern. Mutation rates of individual microsatellites vary greatly, and the intrinsic DNA features of motif size, sequence, and length contribute to this variation. MSI is used for detecting mismatch repair (MMR)-deficient tumors, which display an MSI-high phenotype due to genome-wide microsatellite destabilization. Because several pathways maintain microsatellite stability, tumors that have undergone other events associated with moderate genome instability may display diagnostic MSI only at specific di- or tetranucleotide markers. We summarize evidence for such alternative MSI forms (A-MSI) in sporadic cancers, also referred to as MSI-low and EMAST. While the existence of A-MSI is not disputed, there is disagreement about the origin and pathologic significance of this phenomenon. Although ambiguities due to PCR methods may be a source, evidence exists for other mechanisms to explain tumor-specific A-MSI. Some portion of A-MSI tumors may result from random mutational events arising during neoplastic cell evolution. However, this mechanism fails to explain the specificity of A-MSI for di- and tetranucleotide instability. We present evidence supporting the alternative argument that some A-MSI tumors arise by a distinct genetic pathway, and give examples of DNA metabolic pathways that, when altered, may be responsible for instability at specific microsatellite motifs. Finally, we suggest that A-MSI in tumors could be molecular signatures of environmental influences and DNA damage. Importantly, A-MSI occurs in several pre-neoplastic inflammatory states, including inflammatory bowel diseases, consistent with a role of oxidative stress in A-MSI. Understanding the biochemical basis of A-MSI tumor phenotypes will advance the development of new diagnostic tools and positively impact the clinical management of individual cancers.

Chromosomal instability in BRAF mutant, microsatellite stable colorectal cancers

The BRAF oncogene is mutated in 15% of sporadic colorectal cancers. Approximately half of these BRAF mutant cancers demonstrate frequent frameshift mutations termed microsatellite instability (MSI), but are diploid and chromosomally stable. BRAF wild type cancers are typically microsatellite stable (MSS) and instead acquire chromosomal instability (CIN). In these cancers, CIN is associated with a poor outcome. BRAF mutant cancers that are MSS, typically present at an advanced stage and have a particularly poor prognosis. We have previously demonstrated clinical and molecular similarities between MSS cancers with or without a BRAF mutation, and therefore hypothesised that CIN may also be frequent in BRAF mutant/MSS cancers. BRAF mutant/MSS (n = 60), and BRAF wild type/MSS CRCs (n = 90) were investigated for CIN using loss of heterozygosity analysis over twelve loci encompassing chromosomal regions 5q, 8p, 17p and 18q. CIN was frequent in BRAF mutant/MSS cancers (41/57, 72%), which was comparable to the rate found in BRAF wild type/MSS cancers (74/90, 82%). The greatest loss in BRAF mutant/MSS cancers occurred at 8p (26/44, 59%), and the least at 5q (19/49, 39%). CIN in BRAF mutant/MSS cancers correlated with advanced stage (AJCC III/IV: 15/17, 88%; p = 0.02); showed high rates of co-occurrence with the CpG Island Methylator Phenotype (17/23, 74%); and CIN at 18q and 8p associated with worse survival (p = 0.02, p<0.05). This study demonstrates that CIN commonly occurs in advanced BRAF mutant/MSS colorectal cancers where it may contribute to poorer survival, and further highlights molecular similarities occurring between these and BRAF wild type cancers.

Molecular correlates and prognostic significance of SATB1 expression in colorectal cancer

Background

Special AT-rich sequence-binding protein 1 (SATB1) is a global gene regulator that has been reported to confer malignant behavior and associate with poor prognosis in several cancer forms. SATB1 expression has been demonstrated to correlate with unfavourable tumour characteristics in rectal cancer, but its association with clinical outcome in colorectal cancer (CRC) remains unclear. In this study, we examined the prognostic impact of SATB1 expression in CRC, and its association with important molecular characteristics; i.e. beta-catenin overexpression, microsatellite instability (MSI) screening status, and SATB2 expression.

Methods

Immunohistochemical expression of SATB1 and beta-catenin was assessed in tissue microarrays with tumours from 529 incident CRC cases in the prospective population-based Malmö Diet and Cancer Study, previously analysed for SATB2 expression and MSI screening status. Spearmans Rho and Chi-Square tests were used to explore correlations between SATB1 expression, clinicopathological and investigative parameters. Kaplan Meier analysis and Cox proportional hazards modelling were used to explore the impact of SATB1 expression on cancer specific survival (CSS) and overall survival (OS).

Results

SATB1 was expressed in 222 (42%) CRC cases and negative, or sparsely expressed, in adjacent colorectal mucosa (n = 16). SATB1 expression was significantly associated with microsatellite stable tumours (p < 0.001), beta-catenin overexpression (p < 0.001) and SATB2 expression (p < 0.001). While not prognostic in the full cohort, SATB1 expression was significantly associated with poor prognosis in SATB2 negative tumours (HR = 2.63; 95% CI 1.46-4.71; p_interaction = 0.011 for CSS and HR = 2.31; 95% CI 1.32-4.04; p_interaction = 0.015 for OS), remaining significant in multivariable analysis.

Conclusions

The results of this study demonstrate that SATB1 expression in CRC is significantly associated with beta-catenin overexpression, microsatellite stability and SATB2 expression. Furthermore, SATB1 expression is a factor of poor prognosis in SATB2 negative tumours. Altogether, these data indicate an important role for SATB1 in colorectal carcinogenesis and suggest prognostically antagonistic effects of SATB1 and SATB2. The mechanistic basis for these observations warrants further study.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1922643082772076

Aberrant protein expression and frequent allelic loss of MSH3 in colorectal cancer with low-level microsatellite instability

PURPOSE

High level of microsatellite instability (MSI-H) in colorectal cancer (CRC) is caused by the inactivation of mismatch repair (MMR) genes; however, it is unknown for tumors with low level MSI (MSI-L). The protein complex involving MSH3 preferentially recognizes insertion/deletion loops (IDLs) of two to eight bases and di- and tetranucleotide repeats are affected in the majority of MSI-L CRC.

METHODS

We selected 10 and eight MSI-L CRCs from 228 and 204 patients with sporadic and hereditary disease, respectively. The tumors were analyzed for protein expression of MSH3, MSH2, MSH6, MLH1, and PMS2, and for mutations and loss of heterozygosity (LOH) in MSH3.

RESULTS

Four tumors showed a markedly reduced MSH3 expression, whereas all 18 tumors had normal expression of the remaining MMR proteins. Twenty-five different sequence variants were identified. None of these results in a truncated protein, though L902W represents the first constitutional missense mutation in MSH3 predicted to be functional based on conservation among mutS homologues. All variants have also been found in normal DNA of the patients and in controls. LOH intragenic to MSH3 was evident for 12 of 16 (75%) informative tumors.

CONCLUSIONS

Occurrence of sequence variants in normal DNA of the patients and in controls excludes somatic mutations and mutations specific to the CRC patient population, respectively. In contrast, the high frequency of LOH as well as the aberrant protein expression in some tumors indicates an involvement of MSH3 impairment in MSI-L CRC.

A morphologic analysis of sessile serrated polyps observed during routine colonoscopy (with video)

BACKGROUND

Proximal colorectal cancer may arise from sessile serrated polyps (SSPs), which are often inconspicuous during colonoscopy. The gross morphologic characteristics of SSPs have not been systematically described, and this omission may contribute to colonoscopists overlooking them.

OBJECTIVES

To analyze the gross morphologic characteristics of SSPs detected during routine colonoscopy.

DESIGN

Retrospective analysis of high-resolution endoscopic video clips depicting SSPs in situ.

SETTING

Outpatient gastroenterology practice.

PATIENTS

A total of 124 subjects undergoing surveillance or screening colonoscopy after split-dose bowel preparation.

INTERVENTIONS

Analysis of 158 SSPs performed by using validated descriptors.

MAIN OUTCOME MEASUREMENTS

The prevalence of morphologic characteristics related to polyp shape, color, and texture.

RESULTS

A total of 158 SSPs were studied. For 7 visual descriptors, a κ coefficient of ≥ 0.7 was achieved, indicating good to excellent intraobserver agreement. The most prevalent visual descriptors were the presence of a mucous cap (63.9%), rim of debris or bubbles (51.9%), alteration of the contour of a fold (37.3%), and interruption of the underlying mucosal vascular pattern (32.3%). The most common "sentinel signs" were the presence of a mucous cap and alteration of the contour of a mucosal fold (each 24.6%), rim of debris or bubbles (21.7%), and a dome-shaped protuberance (20.3%). When comparing SSPs with adenomatous polyps, the frequencies of 5 of 7 morphologic characteristics and the distribution of sentinel signs differed (P < .01).

LIMITATIONS

Single-site, retrospective analysis.

CONCLUSIONS

SSPs exhibit distinct, variable morphologic characteristics. Many do not display classic features such as a mucous cap. Enhanced appreciation of these morphologic characteristics may improve SSP detection and thereby colorectal cancer prevention.

A serrated colorectal cancer pathway predominates over the classic WNT pathway in patients with hyperplastic polyposis syndrome

Hyperplastic polyposis syndrome (HPS) is characterized by the presence of multiple colorectal serrated polyps and is associated with an increased colorectal cancer (CRC) risk. The mixture of distinct precursor lesion types and malignancies in HPS provides a unique model to study the canonical pathway and a proposed serrated CRC pathway in humans. To establish which CRC pathways play a role in HPS and to obtain new support for the serrated CRC pathway, we assessed the molecular characteristics of polyps (n = 84) and CRCs (n = 19) in 17 patients with HPS versus control groups of various sporadic polyps (n = 59) and sporadic microsatellite-stable CRCs (n = 16). In HPS and sporadic polyps, APC mutations were exclusively identified in adenomas, whereas BRAF mutations were confined to serrated polyps. Six of 19 HPS CRCs (32%) were identified in a serrated polyp. Mutation analysis performed in the CRC and the serrated component of these lesions showed identical BRAF mutations. One HPS CRC was located in an adenoma, both components harboring an identical APC mutation. Overall, 10 of 19 HPS CRCs (53%) carried a BRAF mutation versus none in control group CRCs (P = 0.001). Six BRAF-mutated HPS CRCs (60%) were microsatellite unstable owing to MLH1 methylation. These findings provide novel supporting evidence for the existence of a predominant serrated CRC pathway in HPS, generating microsatellite-stable and microsatellite-instable CRCs.

p53 mutation is common in microsatellite stable, BRAF mutant colorectal cancers

The majority of "serrated pathway" colorectal cancers have mutation of the BRAF oncogene and display the CpG island methylator phenotype (CIMP). Half these cancers have microsatellite instability (MSI) and an excellent prognosis. In the absence of MSI (microsatellite stable, MSS), BRAF mutation has been associated with a particularly poor prognosis. "Traditional pathway" cancers are BRAF wild type. Mutation of p53 is common and this correlates with advanced stage. We therefore hypothesized that p53 mutation would be common in MSS/BRAF mutant colorectal cancer. One thousand and eighty-one colorectal cancers were screened for BRAF mutation to identify two BRAF mutant study groups (MSI: n = 77; MSS: n = 69) and a BRAF wild type control group (n = 101). These were screened for p53 mutation by high resolution melt analysis and classified for CIMP and MGMT methylation by quantitative methylation specific PCR. Molecular data were compared to patient age, gender, tumor location and stage. p53 was mutated significantly more frequently in MSS/BRAF mutant (28/69, 40.6%) compared to MSI/BRAF mutant cancers (13/77, 16.9%), but this mutation rate did not differ from MSS/BRAF wild type cancers (47/101, 46.5%)(p < 0.0001). CIMP was less common in MSS/BRAF mutant (26/47, 55.3%) compared to MSI/BRAF mutant cancers (41/54, 75.9%), but was more common than in MSS/BRAF wild type cancers (3/85, 3.5%) (p < 0.0001). MSS/BRAF mutant cancers were more commonly proximal (38/54, 70.3%), but were similar to MSS/BRAF wild type cancers in terms of patient age, gender distribution and stage at presentation. MSS/BRAF mutant cancers share molecular and clinical features of both the serrated and traditional pathways of colorectal tumorigenesis.

Overexpression of neurone glial-related cell adhesion molecule is an independent predictor of poor prognosis in advanced colorectal cancer

A downstream target of the Wnt pathway, neurone glial-related cell adhesion molecule (Nr-CAM) has recently been implicated in human cancer development. However, its role in colorectal cancer (CRC) pathobiology and clinical relevance remains unknown. In this study, we examined the clinical significance of Nr-CAM protein expression in a retrospective series of 428 CRCs using immunohistochemistry and tissue microarrays. Cox proportional hazards regression was used to calculate hazard ratios (HR) of mortality according to various clinicopathological features and molecular markers. All CRC samples were immunoreactive for Nr-CAM protein expression, compared to 10 ⁄ 245 (4%) matched normal tissue (P < 0.0001). Of 428 CRC samples, 97 (23%) showed Nr-CAM overexpression, which was significantly associated with nodal (P = 0.012) and distant (P = 0.039) metastasis, but not with extent of local invasion or tumor size. Additionally, Nr-CAM overexpression was associated with vascular invasion (P = 0.0029), p53 expression (P = 0.036), and peritoneal metastasis at diagnosis (P = 0.013). In a multivariate model adjusted for other clinicopathological predictors of survival, Nr-CAM overexpression correlated with a significant increase in disease-specific (HR 1.66; 95% confidence interval 1.11-2.47; P = 0.014) and overall mortality (HR 1.57; 95% confidence interval 1.07-2.30; P = 0.023) in advanced but not early stage disease. Notably, 5-fluorouracil-based chemotherapy conferred significant survival benefit to patients with tumors negative for Nr-CAM overexpression but not to those with Nr-CAM overexpressed tumors. In conclusion, Nr-CAM protein expression is upregulated in CRC tissues. Nr-CAM overexpression is an independent marker of poor prognosis among advanced CRC patients, and is a possible predictive marker for non-beneficence to 5-fluorouracil- based chemotherapy.

Up and downregulation of p16(Ink4a) expression in BRAF-mutated polyps/adenomas indicates a senescence barrier in the serrated route to colon cancer

P16(Ink4a) is an important factor in carcinogenesis and its expression can be linked to oncogene-induced senescence. Oncogene-induced senescence is characterized by growth arrest and occurs as a consequence of oncogene activation due to KRAS or BRAF mutation. It has been shown that the induction of p16(Ink4a) in premalignant lesions and its loss during malignant transformation is an important mechanism in the carcinogenesis of several tumours. Loss of p16(Ink4a) is often caused by CDKN2A promoter hypermethylation. This mechanism of gene silencing is associated with the CpG island methylator phenotype (CIMP) in colorectal carcinomas, which is characterized by widespread promoter methylation. In particular, colorectal carcinomas with BRAF mutations have been shown to be strongly associated with CIMP. Also, BRAF mutations are strongly correlated with the serrated route to colorectal cancer. In this study, we investigated p16(Ink4a) expression and promoter methylation in BRAF-mutated serrated lesions of the colon. P16(Ink4a) expression was found to be upregulated in premalignant lesions and was lost in invasive serrated carcinomas. P16(Ink4a) expression and Ki67 expression were mutually exclusive, indicating that p16(Ink4a) acts as cell cycle inhibitor. Additionally, progression of malignant transformation in serrated lesions was accompanied by increasing methylation of the CDKN2A promoter. Therefore, our data provide evidence for oncogene-induced senescence in the serrated route to colorectal cancer with BRAF mutation and upregulation of p16(Ink4a) expression appears to be a useful indicator of induction of senescence. Loss of p16(Ink4a) expression occurs during malignant transformation and is caused mainly by aberrant methylation of the CDKN2A promoter.

[Histopathological diagnosis and differential diagnosis of colorectal serrated polys: findings of a consensus conference of the working group "gastroenterological pathology of the German Society of Pathology"]

Until recently, two major types of colorectal epithelial polyps were distinguished: the adenoma and the hyperplastic polyp. While adenomas - because of their cytological atypia - were recognized as precursor lesions for colorectal carcinoma, hyperplastic polyps were perceived as harmless lesions without any potential for malignant progression, mainly because hyperplastic polyps lack cytological atypia. Meanwhile, it is evident that the lesions formerly classified as hyperplastic represent a heterogeneous group of polyps, some of which exhibit a significant risk of neoplastic progression. These lesions show characteristic epigenetic alterations not commonly seen in colorectal adenomas and progress to colorectal carcinoma via the so-called serrated pathway (CIMP pathway). This group of polyps is comprised not only of hyperplastic polyps, but also of sessile serrated adenomas (SSA), traditional serrated adenomas (TSA) and mixed polyps, showing serrated and "classical" adenomatous features. In a consensus conference of the working group of gastroenterological pathology of the German Society of Pathology, standardization of nomenclature and diagnostic criteria as well as recommendations for clinical management of these serrated polyps were formulated and are presented herein.

Sporadic colorectal carcinomas with low-level microsatellite instability: a distinct subgroup with specific clinicopathological and molecular features

PURPOSE

The biologic significance of low-level microsatellite instability (MSI) in sporadic colorectal cancers (CRCs) is not clearly defined. In particular, the relationship of MSI-low to MSI-high and microsatellite stable (MSS) tumours is currently under debate and the prognostic impact of these genetic changes remains unclear. The objective of this study was to investigate whether sporadic MSI-low CRCs have different clinicopathological and molecular features from MSS and MSI-high tumours.

METHODS

A series of 184 primary sporadic CRCs were divided, according to the level of MSI, into three groups (94 MSS, 22 MSI-low and 68 MSI-high) and were analyzed for baseline clinicopathological features and outcome, allelic losses at 18q, 8p and 4p chromosomes and immunohistochemical expression of MGMT, hMlh1, hMsh2, Fhit, Cox-2, p21 and p27 proteins.

RESULTS

MSI-low tumours were more frequently distal (59.1%) whereas MSS tumours had a strong predilection for distal (72.3%) and MSI-high tumours for proximal location (54.4%; p = 0.003). When compared with MSI-high tumors, MSI-low CRCs were adenocarcinoma, not otherwise specified (p = 0.0138) and well to/moderately differentiated (p = 0.027). MSI-low CRCs also showed specific molecular features including intermediate 18q allelic losses, altered MGMT and Cox-2 expression. Finally, the 5-year overall survival rates were 79% for MSI-low, 40.3% for MSS and 71% for MSI-high CRCs (p = 0.0160 MSS vs. MSI-low groups).

CONCLUSIONS

Sporadic MSI-low CRCs display characteristic clinicopathological and genetic features that distinguish them from MSS CRCs.

Frequent mutations of KRAS in addition to BRAF in colorectal serrated adenocarcinoma

AIMS

To define the occurrence of KRAS and BRAF mutations, microsatellite instability (MSI), and MGMT and hMLH1 methylation and expression in colorectal serrated adenocarcinoma.

METHODS AND RESULTS

KRAS codon 12/13 and 59/61 and BRAF V600E mutations, MSI, and MGMT and hMLH1 methylation and expression in 42 serrated adenocarcinomas and 17 serrated adenomas were compared with those in 59 non-serrated colorectal carcinomas (CRCs) and nine adenomas. KRAS and BRAF mutations were observed in 45% and 33% of serrated adenocarcinomas and in 27% and 0% of non-serrated CRCs (P < 0.001). The KRAS c12G→A transition was the predominant type of mutation in serrated adenocarcinomas. Forty-two per cent of BRAF-mutated serrated adenocarcinomas showed high-level MSI (MSI-H) (P = 0.075), 100% showed hMLH1 methylation (P = 0.001) and 90.9% showed MGMT methylation (P = 0.019). Fifty-six per cent of serrated adenocarcinomas with microsatellite stability/low-level microsatellite instability harboured KRAS mutations. In non-serrated cancers, KRAS mutations were not associated with MSI status.

CONCLUSIONS

A high combined mutation rate (79-82%) of KRAS and BRAF in serrated adenomas and adenocarcinomas indicates that mitogen-activated protein kinase activation is a crucial part of the serrated pathway. BRAF mutations are specific for serrated adenocarcinoma and identify a subset of serrated adenocarcinomas with gene methylation and a tendency for MSI-H. A high frequency of KRAS mutations in serrated adenocarcinomas suggests that a significant proportion of KRAS-mutated CRCs originate from serrated precursors, thus challenging the traditional model of Vogelstein.

Investigating the potential role of genetic and epigenetic variation of DNA methyltransferase genes in hyperplastic polyposis syndrome

Background

Hyperplastic Polyposis Syndrome (HPS) is a condition associated with multiple serrated polyps, and an increased risk of colorectal cancer (CRC). At least half of CRCs arising in HPS show a CpG island methylator phenotype (CIMP), potentially linked to aberrant DNA methyltransferase (DNMT) activity. CIMP is associated with methylation of tumor suppressor genes including regulators of DNA mismatch repair (such as MLH1, MGMT), and negative regulators of Wnt signaling (such as WIF1). In this study, we investigated the potential for interaction of genetic and epigenetic variation in DNMT genes, in the aetiology of HPS.

Methods

We utilized high resolution melting (HRM) analysis to screen 45 cases with HPS for novel sequence variants in DNMT1, DNMT3A, DNMT3B, and DNMT3L. 21 polyps from 13 patients were screened for BRAF and KRAS mutations, with assessment of promoter methylation in the DNMT1, DNMT3A, DNMT3B, DNMT3L MLH1, MGMT, and WIF1 gene promoters.

Results

No pathologic germline mutations were observed in any DNA-methyltransferase gene. However, the T allele of rs62106244 (intron 10 of DNMT1 gene) was over-represented in cases with HPS (p<0.01) compared with population controls. The DNMT1, DNMT3A and DNMT3B promoters were unmethylated in all instances. Interestingly, the DNMT3L promoter showed low levels of methylation in polyps and normal colonic mucosa relative to matched disease free cells with methylation level negatively correlated to expression level in normal colonic tissue. DNMT3L promoter hypomethylation was more often found in polyps harbouring KRAS mutations (p = 0.0053). BRAF mutations were common (11 out of 21 polyps), whilst KRAS mutations were identified in 4 of 21 polyps.

Conclusions

Genetic or epigenetic alterations in DNMT genes do not appear to be associated with HPS, but further investigation of genetic variation at rs62106244 is justified given the high frequency of the minor allele in this case series.

V600EBraf induces gastrointestinal crypt senescence and promotes tumour progression through enhanced CpG methylation of p16INK4a

The majority of human colorectal cancers (CRCs) are initiated by mutations arising in the adenomatous polyposis coli (APC) tumour suppressor gene. However, a new class of non-APC mutated CRCs has been defined that have a serrated histopathology and carry the ^V600EBRAF oncogene. Here we have investigated the pathogenesis of serrated CRCs by expressing ^V600EBraf in the proliferative cells of the mouse gastrointestinal tract. We show that the oncogene drives an initial burst of Mek-dependent proliferation, leading to the formation of hyperplastic crypts. This is associated with β-catenin nuclear localization by a mechanism involving Mapk/Erk kinase (Mek)-dependent, Akt-independent phosphorylation of Gsk3β. However, hyperplastic crypts remain dormant for prolonged periods due to the induction of crypt senescence accompanied by upregulation of senescence-associated β-galactosidase and p16^Ink4a. We show that tumour progression is associated with down-regulation of p16^Ink4a through enhanced CpG methylation of exon 1 and knockout of Cdkn2a confirms this gene is a barrier to tumour progression. Our studies identify ^V600EBRAF as an early genetic driver mutation in serrated CRCs and indicate that, unlike APC-mutated cancers, this subtype arises by the bypassing of a ^V600EBraf driven oncogene-induced senescence programme.

Genotype to phenotype: analyzing the effects of inherited mutations in colorectal cancer families

With improvements to DNA sequencing technologies, including the advent of massively parallel sequencing to perform "deep sequencing" of tissue samples, the ability to determine all of the nucleotide variations in a tumor becomes a possibility. This information will allow us to more fully understand the heterogeneity within each tumor, as well as to identify novel genes involved in cancer development. However, the new challenge that arises will be to interpret the pathogenic significance of each genetic variant. The enormity and complexity of this challenge can be demonstrated by focusing on just the genes involved in the hereditary colon cancer syndromes, familial adenomatous polyposis (FAP) and hereditary non-polyposis coli (HNPCC). The genes responsible for each disease were identified almost two decades ago -APC for FAP and the MMR genes for HNPCC - and a large number of germline variations have been identified in these genes in hereditary cancer patients. However, relating the effect of an individual genotype to phenotype is not always straightforward. This review focuses on the roles of the APC and MMR genes in tumor development and the work that has been done to relate different variants in each gene to functional aberrations and ultimately tumorigenesis. By considering the work that has already been done on two well-defined diseases with clear genetic associations, one can begin to understand the challenges that lie ahead as new genes and gene mutations are discovered through tumor sequencing.

Promoter methylation status of hMLH1, MGMT, and CDKN2A/p16 in colorectal adenomas

AIM: To investigate aberrant DNA methylation of CpG islands and subsequent low- or high-level DNA microsatellite instability (MSI) which is assumed to drive colon carcinogenesis.

METHODS: DNA of healthy individuals, adenoma (tubular or villous/tubulovillous) patients, and colorectal carcinoma patients who underwent colonoscopy was used for assessing the prevalence of aberrant DNA methylation of human DNA mismatch repair gene mutator L homologue 1 (hMLH1), Cyclin-dependent kinase inhibitor 2A (CDKN2A/p16), and O-6-methylguanine DNA methyltransferase (MGMT), as well as their relation to MSI.

RESULTS: The frequency of promoter methylation for each locus increased in the sequence healthy tissue/adenoma/carcinoma. MGMT showed the highest frequency in each group. MGMT and CDKN2A/p16 presented a statistically significant increase in promoter methylation between the less and more tumorigenic forms of colorectal adenomas (tubular vs tubullovillous and villous adenomas). All patients with tubulovillous/villous adenomas, as well as all colorectal cancer patients, showed promoter methylation in at least one of the examined loci. These findings suggest a potentially crucial role for methylation in the polyp/adenoma to cancer progression in colorectal carcinogenesis. MSI and methylation seem to be interdependent, as simultaneous hMLH1, CDKN2A/p16, and MGMT promoter methylation was present in 8/9 colorectal cancer patients showing the MSI phenotype.

CONCLUSION: Methylation analysis of hMLH1, CDKN2A/p16, and MGMT revealed specific methylation profiles for tubular adenomas, tubulovillous/villous adenomas, and colorectal cancers, supporting the use of these alterations in assessment of colorectal tumorigenesis.

Serrated polyps of the colon and rectum (hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, and mixed polyps)-proposal for diagnostic criteria

Until recently, two major types of colorectal epithelial polyps were distinguished: the adenoma and the hyperplastic polyp. While adenomas-because of their cytological atypia-were recognized as the precursor lesions for colorectal carcinoma, hyperplastic polyps were perceived as harmless lesions without any potential for malignant progression mainly because hyperplastic polyps are missing cytological atypia. Meanwhile, it is recognized that the lesions, formerly classified as hyperplastic, represent a heterogeneous group of polyps with characteristic serrated morphology some of which exhibit a significant risk of neoplastic progression. These serrated lesions show characteristic epigenetic alterations not commonly seen in colorectal adenomas and progress to colorectal carcinoma via the so-called serrated pathway (CpG-island-methylation-phenotype pathway). This group of polyps is comprised not only of hyperplastic polyps, but also of sessile serrated adenomas, traditional serrated adenomas and mixed polyps, showing serrated and "classical" adenomatous features. Diagnostic criteria and nomenclature for these lesions are not uniform and, therefore, somewhat confusing. In a consensus conference of the Working Group of Gastroenterological Pathology of the German Society of Pathology, standardization of nomenclature and diagnostic criteria as well as recommendations for clinical management of these serrated polyps were formulated and are presented herein.

Serrated adenoma: a distinct form of non-polypoid colorectal neoplasia?

Until recently, 2 major forms of colorectal polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were known to represent a precursor to colorectal cancer, whereas hyperplastic polyps were viewed as nonneoplastic, having no potential for progression to malignancy. We now recognize, however, that the lesions diagnosed as hyperplastic polyps in the past represent a heterogeneous group of polyps, some of which truly are hyperplastic, and others that truly have a significant risk for transformation to colorectal cancer. These polyps have a characteristic serrated architecture, and include not only hyperplastic polyps but also the recently recognized serrated adenomas. Serrated adenomas occur in 2 forms: the traditional serrated adenoma, which is usually a polypoid lesion endoscopically, and the sessile serrated adenoma, a flat or slightly raised, usually right-sided lesion. Serrated adenomas of both types show characteristic molecular alterations not commonly seen in traditional colorectal adenomas, and probably progress to colorectal cancer by means of a different pathway, the so-called serrated neoplasia pathway. The morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development are discussed.

Epigenomic diversity of colorectal cancer indicated by LINE-1 methylation in a database of 869 tumors

BACKGROUND

Genome-wide DNA hypomethylation plays a role in genomic instability and carcinogenesis. LINE-1 (L1 retrotransposon) constitutes a substantial portion of the human genome, and LINE-1 methylation correlates with global DNA methylation status. LINE-1 hypomethylation in colon cancer has been strongly associated with poor prognosis. However, whether LINE-1 hypomethylators constitute a distinct cancer subtype remains uncertain. Recent evidence for concordant LINE-1 hypomethylation within synchronous colorectal cancer pairs suggests the presence of a non-stochastic mechanism influencing tumor LINE-1 methylation level. Thus, it is of particular interest to examine whether its wide variation can be attributed to clinical, pathologic or molecular features.

DESIGN

Utilizing a database of 869 colorectal cancers in two prospective cohort studies, we constructed multivariate linear and logistic regression models for LINE-1 methylation (quantified by Pyrosequencing). Variables included age, sex, body mass index, family history of colorectal cancer, smoking status, tumor location, stage, grade, mucinous component, signet ring cells, tumor infiltrating lymphocytes, CpG island methylator phenotype (CIMP), microsatellite instability, expression of TP53 (p53), CDKN1A (p21), CTNNB1 (beta-catenin), PTGS2 (cyclooxygenase-2), and FASN, and mutations in KRAS, BRAF, and PIK3CA.

RESULTS

Tumoral LINE-1 methylation ranged from 23.1 to 90.3 of 0-100 scale (mean 61.4; median 62.3; standard deviation 9.6), and distributed approximately normally except for extreme hypomethylators [LINE-1 methylation < 40; N = 22 (2.5%), which were far more than what could be expected by normal distribution]. LINE-1 extreme hypomethylators were significantly associated with younger patients (p = 0.0058). Residual plot by multivariate linear regression showed that LINE-1 extreme hypomethylators clustered as one distinct group, separate from the main tumor group. The multivariate linear regression model could explain 8.4% of the total variability of LINE-1 methylation (R-square = 0.084). Multivariate logistic regression models for binary LINE-1 hypomethylation outcomes (cutoffs of 40, 50 and 60) showed at most fair predictive ability (area under receiver operator characteristics curve < 0.63).

CONCLUSIONS

LINE-1 extreme hypomethylators appear to constitute a previously-unrecognized, distinct subtype of colorectal cancers, which needs to be confirmed by additional studies. Our tumor LINE-1 methylation data indicate enormous epigenomic diversity of individual colorectal cancers.

Differential colorectal carcinogenesis: Molecular basis and clinical relevance

Colorectal cancer (CCR) is one of the most frequent cancers in developed countries. It poses a major public health problem and there is renewed interest in understanding the basic principles of the molecular biology of colorectal cancer. It has been established that sporadic CCRs can arise from at least two different carcinogenic pathways. The traditional pathway, also called the suppressor or chromosomal instability pathway, follows the Fearon and Vogelstein model and shows mutation in classical oncogenes and tumour suppressor genes, such as K-ras, adenomatous polyposis coli, deleted in colorectal cancer, or p53. Alterations in the Wnt pathway are also very common in this type of tumour. The second main colorectal carcinogenesis pathway is the mutator pathway. This pathway is present in nearly 15% of all cases of sporadic colorectal cancer. It is characterized by the presence of mutations in the microsatellite sequences caused by a defect in the DNA mismatch repair genes, mostly in hMLH1 or hMSH2. These two pathways have clear molecular differences, which will be reviewed in this article, but they also present distinct histopathological features. More strikingly, their clinical behaviours are completely different, having the “mutator” tumours a better outcome than the “suppressor” tumours.

Development and progression of colorectal neoplasia

A variety of genetic and molecular alterations underlie the development and progression of colorectal neoplasia (CRN). Most of these cancers arise sporadically due to multiple somatic mutations and genetic instability. Genetic instability includes chromosomal instability (CIN) and microsatellite instability (MSI), which is observed in most hereditary non-polyposis colon cancers (HNPCCs) and accounts for a small proportion of sporadic CRN. Although many biomarkers have been used in the diagnosis and prediction of the clinical outcomes of CRNs, no single marker has established value. New markers and genes associated with the development and progression of CRNs are being discovered at an accelerated rate. CRN is a heterogeneous disease, especially with respect to the anatomic location of the tumor, race/ethnicity differences, and genetic and dietary interactions that influence its development and progression and act as confounders. Hence, efforts related to biomarker discovery should focus on identification of individual differences based on tumor stage, tumor anatomic location, and race/ethnicity; on the discovery of molecules (genes, mRNA transcripts, and proteins) relevant to these differences; and on development of therapeutic approaches to target these molecules in developing personalized medicine. Such strategies have the potential of reducing the personal and socio-economic burden of CRNs. Here, we systematically review molecular and other pathologic features as they relate to the development, early detection, diagnosis, prognosis, progression, and prevention of CRNs, especially colorectal cancers (CRCs).

Methylation in p14(ARF) is frequently observed in colorectal cancer with low-level microsatellite instability

Colorectal cancer (CRC) can be classified as high-level microsatellite instability (MSI-H), low-level MSI (MSI-L) and microsatellite stable (MSS) depending on levels of MSI. MSI-H CRC relies on a distinct molecular pathway due to the mismatch repair (MMR) deficiency and shows methylation in multiple gene promoters. The genetic pathway leading to MSI-L is unknown, although higher levels of promoter methylation are observed in this group compared with MSS CRCs. This study explored how promoter methylation affects MSI phenotype, by analysing the methylation status of eight CRC-related promoters, MSI phenotype and KRAS/BRAF mutations in a series of 234 CRCs. Promoter methylation of p14(ARF) was significantly related to MSI-L CRC with KRAS mutation. The MSI-H phenotype was related to methylation of MLH1 as expected, while the MSS phenotype was related to methylation of p16(INK4a) and O(6)-methylguanine-DNA methyltransferase, although this was not statistically significant. Thus, promoter methylation of p14(ARF) could be a significant alteration leading to CRC with MSI-L.

[Tissue microarray (TMA) validated progression markers in colorectal cancer using antibody microarrays]

BACKGROUND

The exact molecular biological background of colorectal cancer development and progression are not hitherto known. Using microarray systems, hundreds or thousands of parameters could be examined simultaneously for answering the mentioned questions.

AIM

To identify possible protein markers of colorectal cancer development and progression using antibody array, and the validation of these markers on tissue microarrays done with colorectal cancer samples. Furthermore, to determine colorectal cancer diagnostic marker combination in protein level.

MATERIALS AND METHODS

Surgically resected samples from ten Dukes B and six Dukes D stage patients containing both diseased and un-involved parts of the colon were freshly frozen. The samples were homogenized and the extracted proteins were used for Clontech AB500 arrays. Twelve selected genes were validated on tissue microarrays.

RESULTS

The expression of 67 proteins was altered (p < 0.05) between the normal colon and cancerous samples. These genes are related to apoptosis (n = 5), cell cycle regulation (n = 7), transcription (n = 4), DNA replication (n = 6) and other cell functions, such as transport and cell adhesion (n = 45). Twelve potential markers were immunohistochemically validated on morphological level by using tissue microarrays (CYCA1, HSP60, TOP1, APC, CBP, ERK, EGFR, C-myc, Cald, DARPP32, MRE11A, AR, EPS8).

CONCLUSION

Based on these results, validated colorectal cancer development related protein markers are involved in a wide spectrum of cell functions such as apoptosis, cell cycle regulation, and signal transduction. A set of six proteins has been determined, which helps to differentiate between normal specimen, early and late stage colorectal cancer with high sensitivity and specificity.

Colonic adenoma patients have higher incidence of hyperplastic polyps on surveillance colonoscopy

OBJECTIVES

To determine the incidence of hyperplastic polyps in patients undergoing surveillance colonoscopy and to compare with the prevalence in individuals undergoing index colonoscopy.

PATIENTS AND METHODS

This prospective observational study included patients with index colonoscopy findings of adenomas, adenoma with concomitant hyperplastic polyps and advanced neoplasia who subsequently underwent surveillance colonoscopy. Patient characteristics, indications for colonoscopy, interval between examinations and findings were recorded. These findings were compared with our control group that comprised of patients who underwent index colonoscopy during the same period.

RESULTS

Study group consisted of 108 patients (median age 61.5 years) who underwent index colonoscopy for indications including, weight loss, rectal bleeding, altered bowel habits and anaemia. On index colonoscopy, adenomas, adenoma with concomitant hyperplastic polyps and advanced neoplasia were present in 61, 35 and 12 patients, respectively. Surveillance colonoscopy was performed after a mean follow-up period of 29 +/- 17 months. Findings on surveillance examination included hyperplastic polyps in 35 and 57% of patients with past adenomas and adenoma with concomitant hyperplastic polyps, respectively. Control group included 3852 symptomatic patients who had index colonoscopy (median age, 65 years). Hyperplastic polyps, adenomas and advanced neoplasia were found in 155 (4%), 388 (10%) and 60 (1.5%) of patients, respectively. Hyperplastic polyps and adenoma were significantly higher in study group as compared with control group (P >0.5).

CONCLUSION

Incidence of hyperplastic polyps is significantly higher on surveillance colonoscopy as compared with the prevalence on index colonoscopy. This may signify a continuous spectrum of biological evolution between hyperplastic polyps and adenomas.

Aurora-A expression is independently associated with chromosomal instability in colorectal cancer

AURKA (the official symbol for Aurora-A, STK15, or BTAK) regulates the function of centrosomes, spindles, and kinetochores for proper mitotic progression. AURKA overexpression is observed in various cancers including colon cancer, and a link between AURKA and chromosomal instability (CIN) has been proposed. However, no study has comprehensively examined AURKA expression in relation to CIN or prognosis using a large number of tumors. Using 517 colorectal cancers in two prospective cohort studies, we detected AURKA overexpression (by immunohistochemistry) in 98 tumors (19%). We assessed other molecular events including loss of heterozygosity (LOH) in 2p, 5q, 17q, and 18q, the CpG island methylation phenotype (CIMP), and microsatellite instability (MSI). Prognostic significance of AURKA was evaluated by Cox regression and Kaplan-Meier method. In both univariate and multivariate logistic regressions, AURKA overexpression was significantly associated with CIN (defined as the presence of LOH in any of the chromosomal segments; multivariate odds ratio, 2.97; 95% confidence interval, 1.40-6.29; P = .0045). In multivariate analysis, AURKA was associated with cyclin D1 expression (P = .010) and inversely with PIK3CA mutation (P=.014), fatty acid synthase expression (P=.028), and family history of colorectal cancer (P = .050), but not with sex, age, body mass index, tumor location, stage, CIMP, MSI, KRAS, BRAF, BMI, LINE-1 hypomethylation, p53, p21, beta-catenin, or cyclooxygenase 2. AURKA was not significantly associated with clinical outcome or survival. In conclusion, AURKA overexpression is independently associated with CIN in colorectal cancer, supporting a potential role of Aurora kinase-A in colorectal carcinogenesis through genomic instability (rather than epigenomic instability).

Mismatch repair, p53 and chromosomal aberrations in primary colorectal carcinomas

Colorectal carcinoma progresses via at least two genetic pathways. Microsatellite instability, due to defective mismatch repair genes, characterizes one pathway and gross chromosomal instability another. The involvement of p53 and mismatch repair gene abnormalities within these pathways has not been fully explored. We aimed to investigate the relationships of p53 and mismatch repair gene defects on gross chromosomal aberrations detected by comparative genomic hybridization in 49 colorectal carcinomas. Tumours demonstrating loss of expression for hMLH1 or hMSH2 proteins demonstrated a highly significant attenuation in the number of gross chromosomal aberrations (p = 0.007) and were less likely to show p53 overexpression (p = 0.02). Within the mismatch repair normal tumours, p53 status did not affect the total number of chromosomal aberrations but p53 overexpression was significantly associated with a higher frequency of amplifications at 8q22-ter and at 13q21-22. Colorectal cancer demonstrates distinct molecular phenotypes and should be sub-classified accordingly.

Genetic prognostic and predictive markers in colorectal cancer

Despite many studies of the likely survival outcome of individual patients with colorectal cancer, our knowledge of this subject remains poor. Until recently, we had virtually no understanding of individual responses to therapy, but the discovery of the KRAS mutation as a marker of probable failure of epidermal growth factor receptor (EGFR)-targeted therapy is a first step in the tailoring of treatment to the individual. With the application of molecular analyses, as well as the ability to perform high-throughput screens, there has been an explosive increase in the number of markers thought to be associated with prognosis and treatment outcome in this disease. In this Review, we attempt to summarize the sometimes confusing findings, and critically assess those markers already in the public domain.

Serrated polyps and colorectal cancer: new pathway to malignancy

Until recently, two major forms of colorectal epithelial polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were perceived to represent the precursor to colorectal cancer, whereas hyperplastic polyps were viewed as innocuous lesions with no potential for progression to malignancy. We now recognize, however, that the lesions formerly classified as hyperplastic actually represent a heterogeneous group of polyps, some of which have a significant risk for neoplastic transformation. These serrated polyps include not only hyperplastic polyps but also traditional serrated adenomas and sessile serrated adenomas. These polyps demonstrate characteristic molecular alterations not commonly seen in colorectal adenomas, and they probably progress to colorectal cancer by means of a new pathway: the serrated neoplasia pathway. The morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development are discussed herein.