Analysis of K-ras, BRAF, and PIK3CA mutations in laterally-spreading tumors of the colorectum

A Systematic Review and Meta-analysis on the Occurrence of Biomarker Mutation in Colorectal Cancer among the Asian Population

Globally, colorectal carcinoma (CRC) is the third most common cancer and the third major cause of cancer-related death in both sexes. KRAS and BRAF mutations are almost mutually exclusively involved in the pathogenesis of CRC. Both are major culprits in treatment failure and poor prognosis for CRC. Method. A systematic review and meta-analysis of various research was done following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. This trial is registered with PROSPERO CRD42021256452. The initial search included 646 articles; after the removal of noneligible studies, a total of 88 studies was finally selected. Data analysis was carried out using OpenMeta Analyst and Comprehensive Meta-Analysis 3.0 (CMA 3.0) software to investigate the prevalence of KRAS and BRAF mutations among patients with CRC in Asia. Results. The meta-analysis comprises of 25,525 sample sizes from Asia with most being male 15,743/25525 (61.7%). Overall prevalence of KRAS mutations was (59/88) 36.3% (95% CI: 34.5-38.2) with I 2 = 85.54% (P value < 0.001). In 43/59 studies, frequency of KRAS mutations was majorly in codon 12 (76.6% (95% CI: 74.2-78.0)) and less in codon 13 (21.0% (95% CI: 19.1-23.0)). Overall prevalence of BRAF mutations was 5.6% (95% CI: 3.9-8.0) with I 2 = 94.00% (P value < 0.001). When stratified according to location, a higher prevalence was observed in Indonesia (71.8%) while Pakistan has the lowest (13.5%). Conclusion. Total prevalence of KRAS and BRAF mutations in CRC was 36.6% and 5.6%, respectively, and the results conformed with several published studies on KRAS and BRAF mutations.

Imaging features associated with survival outcomes among colorectal cancer patients with and without KRAS mutation

Background

Mutations in Kirsten rat sarcoma proto-oncogene (KRAS) have been shown to be associated with advanced-stage colorectal cancer (CRC), negative disease outcomes, and poor response to treatment. The purpose of this study was to investigate which CT features are biomarkers for KRAS gene mutation and impact the survival outcomes of colorectal cancer patients.

Results

Of the 113 CRC patients included in the study, 46 had KRAS mutations (40.71%) and 67 had no mutations (59.29%). Regional lymph node necrosis was the only imaging feature significantly associated with KRAS mutation (P = 0.011). Higher T staging and liver, lung, and distant metastasis were prognostic factors for CRC (P = 0.014, P < 0.001, P = 0.022, P < 0.001, respectively). There were no significant differences in overall survival between patients with KRAS mutations and those without (P = 0.159). However, in patients with no KRAS mutation, those with CRC on the left side had a significantly higher rate of survival than those with CRC on the right (P = 0.005).

Conclusion

Regional lymph node necrosis may be an imaging biomarker of CRC with KRAS mutation, possibly indicating poor prognosis.

Two histologic compartments in nonpolypoid conventional colon adenomas

Two intertwined compartments coexisting in nonpolypoid conventional (i.e. tubular or villous) adenomas are highlighted in this review: one built of dysplastic tissue on top and the other portraying crypts with irregular, corrupted shapes, albeit lined with normal epithelium, below. The latter compartment has remained unattended in the literature. Recently, however, the histologic characteristics of the nondysplastic compartment in nonpolypoid conventional adenomas were closely examined, and some of its biological attributes were unveiled. Studies with the proliferation marker ki67 showed that the crypts with irregular, corrupted shapes in the nondysplastic compartment displayed haphazardly distributed proliferating cell-domains. Given that the proliferating cells are generated by stem cells, the relocation of proliferating cell-domains in those crypts seems to be the result of a reorganization of the stem cells within the crypts. The abnormal distribution of proliferating cells, the finding of p53-upregulated cells, and of crypts in asymmetric fission suggest that the crypts in that compartment are histo-biologically altered, probably somatically mutated. This new information might contribute to unravel the riddle of crypto-histogenesis of nonpolypoid conventional adenomas of the colon. More research along these lines is necessary, before the biology of the crypts in the nondysplastic compartment can be fully translated into molecular terms.

Analysis of molecular alterations in laterally spreading tumors of the colorectum

BACKGROUND

Colorectal laterally spreading tumors (LSTs) are classified into LST-Gs and LST-NGs, according to macroscopic findings. In the present study, we determined the genetic and epigenetic alterations within colorectal LSTs and protruding adenomas.

METHODS

A crypt isolation method was used to isolate DNA from tumors and normal glands of 73 macroscopically verified colorectal LSTs (histologically defined adenomas; 38 LST-Gs and 35 LST-NGs) and 36 protruding adenomas. The DNA was processed using polymerase chain reaction (PCR) microsatellite assays, single-strand conformation polymorphism (SSCP) assays, and pyrosequencing to detect chromosomal allelic imbalance (AI), mutations in APC, KRAS, and TP53, and the methylation of MLH1, MGMT, CDKN2A, HPP1, RASSF2A, SFRP1, DKK1, ZFP64, and SALL4 genes. In addition, methylation status was examined using the following set of markers: MIN1, MINT2, MINT31, MLH1, and CDKN2A (with classification of negative/low and high). Microsatellite instability (MSI) was also examined.

RESULTS

5q AI and methylation of the SFRP1 and SALL4 genes were common molecular events in both LST-Gs and LST-NGs. Neither MSI nor mutations in BRAF ware observed in the LSTs. TP53 mutations were rarely found in LSTs. The frequencies of KRAS and APC mutations and the methylation levels of ZFP64, RASSF2A, and HPP1 genes were significantly higher in LST-Gs than in LST-NGs. Protruding adenomas showed alterations common to LST-Gs. Negative/low methylation status was common among the three types of tumors.

CONCLUSION

Combined genetic and epigenetic data suggested that the molecular mechanisms of tumorigenesis were different between LST-Gs and LST-NGs.

Epigenetic silencing of NTSR1 is associated with lateral and noninvasive growth of colorectal tumors

Our aim was to identify DNA methylation changes associated with the growth pattern and invasiveness of colorectal cancers (CRCs). Comparison of the methylation statuses of large (≥20 mm in diameter along the colonic surface) noninvasive tumors (NTs) and small (<20 mm in diameter along the colonic surface) invasive tumors (ITs) using CpG island microarray analysis showed neurotensin receptor 1 (NTSR1) to be hypermethylated in large NTs. Quantitative bisulfite pyrosequencing revealed that NTSR1 is frequently methylated in colorectal tumors, with large NTs exhibiting the highest methylation levels. The higher NTSR1 methylation levels were associated with better prognoses. By contrast, NTSR1 copy number gains were most frequent among small ITs. Methylation of NTSR1 was associated with the gene's silencing in CRC cell lines, whereas ectopic expression of NTSR1 promoted proliferation and invasion by CRC cells. Analysis of primary tumors composed of adenomatous and malignant portions revealed that NTSR1 is frequently methylated in the adenomatous portion, while methylation levels are generally lower in the cancerous portions. These results suggest that NTSR1 methylation is associated with lateral and noninvasive growth of colorectal tumors, while low levels of methylation may contribute to the malignant potential through activation of NTSR1. Our data also indicate that NTSR1 methylation may be a prognostic biomarker in CRC.

Gene expression profiling of laterally spreading tumors

Background

Laterally spreading tumors (LSTs) are generally defined as lesions >10 mm in diameter, are characterized by lateral expansion along the luminal wall with a low vertical axis. In contrast to other forms of tumor, LSTs are generally considered to have a superficial growth pattern and the potential for malignancy. We focused on this morphological character of LSTs, and analyzed the gene expression profile of LSTs.

Methods

The expression of 168 genes in 41 colorectal tumor samples (17 LST-adenoma, 12 LST-carcinoma, 12 Ip [pedunculated type of the Paris classification)-adenoma, all of which were 10 mm or more in diameter] was analyzed by PCR array. Based on the results, we investigated the expression levels of genes up-regulated in LST-adenoma, compared to Ip-adenoma, by hierarchical and K-means clustering. To confirm the results of the array analysis, using an additional 60 samples (38 LST-adenoma, 22 Ip-adenoma), we determined the localization of the gene product by immunohistochemical staining.

Result

The expression of 129 genes differed in colorectal tumors from normal mucosa by PCR array analysis. As a result of K-means clustering, the expression levels of five genes, AKT1, BCL2L1, ERBB2, MTA2 and TNFRSF25, were found to be significantly up-regulated (p < 0.05) in LST-adenoma, compared to Ip-adenoma. Immunohistochemical analysis showed that the BCL2L1 protein was significantly and meaningfully up-regulated in LST-adenoma compared to Ip-adenoma (p = 0.010). With respect to apoptosis status in LST-Adenoma, it assumes that BCL2L1 is anti-apoptotic protein, the samples such as BCL2L1 positive and TUNEL negative, or BCL2L1 negative and TUNEL positive are consistent with the assumption. 63.2 % LST-adenoma samples were consistent with the assumption.

Conclusions

LSTs have an unusual profile of gene expression compared to other tumors and BCL2L1 might be concerned in the organization of LSTs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-015-0295-1) contains supplementary material, which is available to authorized users.

Advanced polypectomy and resection techniques

Most colorectal cancer arises from adenomatous polyps. This gradual process may be interrupted by screening and treatment using colonoscopy and polypectomy. Advances in imaging platforms have led to classification systems that facilitate prediction of histologic type and both stratification for and prediction of the risk of invasion. Endoscopic treatment should be the standard of care even for extensive advanced mucosal neoplasm. Technique selection is influenced by lesion features, location, patient factors, and local expertise. Postprocedural complications are more common following advanced resection and endoscopists should be familiar with risk factors, early detection methods, and management.

Mutational profiles of different macroscopic subtypes of colorectal adenoma reveal distinct pathogenetic roles for KRAS, BRAF and PIK3CA

BACKGROUND

Investigations of genetic alterations and correlations with histology or morphology could provide further insights into colorectal carcinogenesis. Nevertheless, such genetic changes were less investigated in adenoma stage and a comprehensive survey of oncogenic mutations in EGFR signaling pathway according to different morphologic subtypes has not been performed.

METHODS

A total of 94 neoplasms, including 34 polypoid adenoma, 16 lateral spreading tumors-granular (LST-G), 20 non-granular LST (LST-NG), and 24 depressed tumors, were subjected for mutational analysis of KRAS (exon 2), BRAF (exon 11 and 15), PIK3CA (exon 9 and 20), AKT (exon 4), EGFR (exon 18-24) and HER2 (exon18-24).

RESULTS

KRAS mutation was noted more frequently in LST (13/36, 36.1%) than polypoid neoplasms (5/34, 14.7%, p = 0.041). When comparing with LST-NG, LST-G had a significantly higher frequency of KRAS mutation. (9/16, 56.3% vs. 4/20, 20.0%, p = 0.024). BRAF mutation (V600E) was found in 2 of 36 (5.6%)LSTs and 1 of 34 (2.9%) polypoid lesions. The two LST lesions with BRAF mutation were pathologically proven to be serrated adenoma. PIK3CA mutation (exon 9 E545K) was identified only in LST (5/36, 13.9%). Mutations in KRAS, BRAF or PIK3CA occurred in a mutually exclusive manner. All mutations were absent in the specimens obtained from depressed type neoplasms.

CONCLUSIONS

Three different macroscopic subtypes of colorectal neoplasms display distinct carcinogenetic pathways in EGFR networking. Further molecular studies of CRCs should take macroscopic subtypes into consideration and highlight the importance of consensus and communication between endoscopic and pathologic diagnosis.

Distinct molecular features of different macroscopic subtypes of colorectal neoplasms

BACKGROUND

Colorectal adenoma develops into cancer with the accumulation of genetic and epigenetic changes. We studied the underlying molecular and clinicopathological features to better understand the heterogeneity of colorectal neoplasms (CRNs).

METHODS

We evaluated both genetic (mutations of KRAS, BRAF, TP53, and PIK3CA, and microsatellite instability [MSI]) and epigenetic (methylation status of nine genes or sequences, including the CpG island methylator phenotype [CIMP] markers) alterations in 158 CRNs including 56 polypoid neoplasms (PNs), 25 granular type laterally spreading tumors (LST-Gs), 48 non-granular type LSTs (LST-NGs), 19 depressed neoplasms (DNs) and 10 small flat-elevated neoplasms (S-FNs) on the basis of macroscopic appearance.

RESULTS

S-FNs showed few molecular changes except SFRP1 methylation. Significant differences in the frequency of KRAS mutations were observed among subtypes (68% for LST-Gs, 36% for PNs, 16% for DNs and 6% for LST-NGs) (P<0.001). By contrast, the frequency of TP53 mutation was higher in DNs than PNs or LST-Gs (32% vs. 5% or 0%, respectively) (P<0.007). We also observed significant differences in the frequency of CIMP between LST-Gs and LST-NGs or PNs (32% vs. 6% or 5%, respectively) (P<0.005). Moreover, the methylation level of LINE-1 was significantly lower in DNs or LST-Gs than in PNs (58.3% or 60.5% vs. 63.2%, P<0.05). PIK3CA mutations were detected only in LSTs. Finally, multivariate analyses showed that macroscopic morphologies were significantly associated with an increased risk of molecular changes (PN or LST-G for KRAS mutation, odds ratio [OR] 9.11; LST-NG or DN for TP53 mutation, OR 5.30; LST-G for PIK3CA mutation, OR 26.53; LST-G or DN for LINE-1 hypomethylation, OR 3.41).

CONCLUSION

We demonstrated that CRNs could be classified into five macroscopic subtypes according to clinicopathological and molecular differences, suggesting that different mechanisms are involved in the pathogenesis of colorectal tumorigenesis.

An appraisal of lymph node ratio in colon and rectal cancer: not one size fits all

BACKGROUND

Lymph node ratio (LNR) is increasingly accepted as a useful prognostic indicator in colorectal cancer. However, variations in methodology, statistical stringency and cohort composition has led to inconsistency in respect of the optimally prognostic LNR.

OBJECTIVE

The aim was to apply a robust regression-based analysis to generate and appraise LNRs optimally prognostic for colon and rectal cancer, both separately and in combination.

METHODS

LNR was established for all patients undergoing either a colonic (n = 379) or rectal (n = 160) cancer resection with curative intent. The optimal LNR associated with disease-free and overall survival were established using a classification and regression tree technique. This process was repeated separately for patients who underwent either colonic or rectal resection and for the combined cohort. Survival associated with differing LNR was estimated using the Kaplan-Meier method and compared using a log-rank test. Relationships between LNR, disease-free survival (DFS) and overall survival (OS) were further characterised using Cox regression analysis. All statistical analyses were conducted in the R programming environment, with statistical significance was taken at a level of p < 0.05.

RESULTS

Optimal LNRs differed between each cohort, when either overall or disease-free survival was considered. LNRs generated from combined cohorts also differed from those generated by individual cohorts. In relation to DFS, LNR values were obtained and included 0.18 for the colon cancer cohort and 0.19 for the rectal and combined colorectal cancer cohorts. In relation to OS, multiple LNR values were obtained for colon and combined cohorts; however, an optimal LNR was not evident in the rectal cancer cohort. Survival patterns according to LNR closely resembled those associated with standard nodal staging.

CONCLUSION

Application of a data-driven approach based on recursive partitioning generates differing lymph node ratios for colon, rectal and combined colorectal cohorts. In each cohort, LNR was similarly prognostic to standard nodal staging in respect to overall and disease-free survival. Overall survival was associated with a multiplicity of LNR values, whilst disease-free survival was associated with a single LNR only. The paper demonstrates the merits of utilising a data-driven approach to determining lymph node ratios from specific patient cohorts. Utilising such an approach enabled the generation of those LNRs that were most associated with particular survival trends in relation to overall and disease-free survival. These differed markedly for colon cancer, rectal cancer and combined cohorts. In general, the survival patterns associated with LNRs generated were similar to those observed with standard nodal staging.

MUC5AC/β-catenin expression and KRAS gene alteration in laterally spreading colorectal tumors

AIM: To clarify differences in mucin phenotype, proliferative activity and oncogenetic alteration among subtypes of colorectal laterally spreading tumor (LST).

METHODS: LSTs, defined as superficial elevated lesions greater than 10 mm in diameter with a low vertical axis, were macroscopically classified into two subtypes: (1) a granular type (Gr-LST) composed of superficially spreading aggregates of nodules forming a flat-based lesion with a granulonodular and uneven surface; and (2) a non-granular type (NGr-LST) with a flat smooth surface and an absence of granulonodular formation. A total of 69 LSTs, comprising 36 Gr-LSTs and 33 NGr-LSTs, were immunohistochemically stained with MUC2, MUC5AC, MUC6, CD10 (markers of gastrointestinal cell lineage), p53, β-catenin and Ki-67 antibodies, and examined for alteration in exon 1 of v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) and exon 15 of v-raf murine sarcoma viral oncogene homologue B1 (BRAF) by polymerase chain reaction followed by direct sequencing.

RESULTS: Histologically, 15 Gr-LST samples were adenomas with low-grade dysplasia (LGD), 12 were high-grade dysplasia (HGD) and 9 were adenocarcinomas invading the submucosa (INV), while 12 NGr-LSTs demonstrated LGD, 14 HGD and 7 INV. In the proximal colon, MUC5AC expression was significantly higher in the Gr-type than the NGr-type. MUC6 was expressed only in NGr-LST. MUC2 or CD10 did not differ. P53 expression demonstrated a significant stepwise increment in progression through LGD-HGD-INV with both types of LST. Nuclear β-catenin expression was significantly higher in the NGr-type. Ki-67 expression was significantly higher in the Gr-type in the lower one third zone of the tumor. In proximal, but not distal colon tumors, the incidence of KRAS provided mutation was significantly higher in the Gr-type harboring a specific mutational pattern (G12V). BRAF mutations (V600E) were detected only in two Gr-LSTs.

CONCLUSION: The two subtypes of LST, especially in the proximal colon, have differing phenotypes of gastrointestinal cell lineage, proliferation and activation of Wnt/β-catenin or RAS/RAF/extracellular signal-regulated kinase signaling.

Wide field endoscopic resection for advanced colonic mucosal neoplasia: current status and future directions

Most colonic adenomas are ≤ 10 mm and are routinely treated by colonoscopic polypectomy with long-term health benefits. Nonpolypoid lesions ≥ 20 mm, whether sessile or flat and laterally spreading, are forms of advanced mucosal neoplasia that cannot be managed by conventional polypectomy and are often referred for surgery. However, the majority of these lesions when carefully assessed are found to be noninvasive and can be safely and effectively treated by advanced endoscopic techniques including endoscopic mucosal resection or endoscopic submucosal dissection with resultant cost, morbidity, and mortality benefits. Lesion assessment is a critical component. Enhanced imaging methods provide the opportunity for accurate pathological characterization, informing treatment decisions, without the need for previous histologic confirmation. Techniques of advanced endoscopic resection are still in evolution and further improvements, including hybrid techniques, bringing less technically challenging and shorter procedures with superior safety can be reasonably expected in the next decade. Safety is a fundamental consideration. Methods of early recognition of complications, risk stratification, and management pathways are being developed and refined. Standardization, validation, and adoption of these technological developments will improve endoscopic interpretation and therapy and in combination with an increased understanding of adenoma molecular biology, will result in a progressively more individualized lesion-specific endoscopic approach. The future of advanced endoscopic resection in the colon is promising, and the next few years should see the boundaries of endoscopic resection expand well beyond the limits of what we know today.