Microsatellite stable colorectal cancers stratified by the BRAF V600E mutation show distinct patterns of chromosomal instability

BRAF-mutated colorectal adenocarcinomas: pathological heterogeneity and clinical implications

Advances in molecular biology have markedly increased our understanding of the heterogeneous molecular landscape of colorectal cancer (CRC). Up to 15% of CRCs harbor the BRAF p.V600E somatic mutation (BRAFmt), a well-established negative prognostic marker in patients with metastatic CRC (mCRC). The BEACON CRC trial set a new standard of care in patients with progressive BRAFmt cancers, consisting of the combination of encorafenib and cetuximab. On these bases, BRAF mutational testing is now recommended in patients with mCRC. However, efforts are needed to further stratify patients carrying this mutation. Here, we discuss the heterogeneous pathologic and molecular landscape of BRAFmt CRCs, focusing on the promises and pitfalls of molecular diagnostics, on novel biomarkers to improve patients' stratification and on the current diagnostic scenario for CRC. We believe that a better stratification based on histopathological features and novel molecular biomarkers should be performed to optimize patient management and therapeutic decision-making.

Evolutionary patterns of chromosomal instability and mismatch repair deficiency in proximal and distal colorectal cancer

AIM

Colorectal carcinomas (CRCs) progress through heterogeneous pathways. The aim of this study was to analyse whether or not the cytogenetic evolution of CRC is linked to tumour site, level of chromosomal imbalance and metastasis.

METHOD

A set of therapy-naïve pT3 CRCs comprising 26 proximal and 49 distal pT3 CRCs was studied by combining immunohistochemistry of mismatch repair (MMR) proteins, microsatellite analyses and molecular karyotyping as well as clinical parameters.

RESULTS

A MMR deficient/microsatellite-unstable (dMMR/MSI-H) status was associated with location of the primary tumour proximal to the splenic flexure, and dMMR/MSI-H tumours presented with significantly lower levels of chromosomal imbalances compared with MMR proficient/microsatellite-stable (pMMR/MSS) tumours. Oncogenetic tree modelling suggested two evolutionary clusters characterized by dMMR/MSI-H and chromosomal instability (CIN), respectively, for both proximal and distal CRCs. In CIN cases, +13q, -18q and +20q were predicted as preferentially early events, and -1p, -4 -and -5q as late events. Separate oncogenetic tree models of proximal and distal cases indicated similar early events independent of tumour site. However, in cases with high CIN defined by more than 10 copy number aberrations, loss of 17p occurred earlier in cytogenetic evolution than in cases showing low to moderate CIN. Differences in the oncogenetic trees were observed for CRCs with lymph node and distant metastasis. Loss of 8p was modelled as an early event in node-positive CRC, while +7p and +8q comprised early events in CRC with distant metastasis.

CONCLUSION

CRCs characterized by CIN follow multiple, interconnected genetic pathways in line with the basic 'Vogelgram' concept proposed for the progression of CRC that places the accumulation of genetic changes at centre of tumour evolution. However, the timing of specific genetic events may favour metastatic potential.

Association Between Baseline Circulating Tumor Cells, Molecular Tumor Profiling, and Clinical Characteristics in a Large Cohort of Chemo-naïve Metastatic Colorectal Cancer Patients Prospectively Collected

BACKGROUND

Clinicopathologic characteristics and prognostic and predictive factors offer valuable guidance when selecting optimal first-line treatment in patients with metastatic colorectal cancer (CRC). The association between baseline circulating tumor cell (bCTC) count, molecular tumor profile, and clinicopathologic features was analyzed in a chemo-naïve metastatic CRC population.

PATIENTS AND METHODS

A total of 1202 patients from the Spanish VISNÚ-1 (FOLFIRINOX/bevacizumab vs. FOLFOX/bevacizumab) and VISNÚ-2 (FOLFIRI/bevacizumab vs. FOLFIRI/cetuximab; RAS-wildtype) studies were analyzed for mutational status and bCTC count. The association between clinicopathologic characteristics and bCTC count, mutational status, and microsatellite instability (MSI) was analyzed in 589 eligible patients.

RESULTS

Interestingly, 41% of the population studied presented ≥3 bCTC count. bCTC count ≥3 was associated with worse performance status (according Eastern Cooperative Oncology Group scale), stage IV at diagnosis, at least 3 metastatic sites, and elevated carcinoembryonic antigen (CEA) levels; but not with RAS or BRAF mutations or high MSI. BRAFmut (BRAF mutated) tumors were associated with right-sided primary tumors, peritoneum, distant lymph node metastasis, and less frequent liver involvement. RASmut (RAS mutated) was associated with worse performance status; stage IV at diagnosis; right-sided primary tumors; liver, lung, and bone metastases; at least 3 metastatic sites; and elevated CEA, whereas PIK3CAmut (PIK3CA mutated) tumors were associated with right-sided primary tumors, high CEA serum levels, and older age. High MSI was associated with right-sided primary tumors, distant lymph nodes metastasis, and lower CEA levels.

CONCLUSIONS

In our study, elevated bCTCs and RASmut were associated with clinicopathologic features known to be associated with poor prognosis; whereas the poor prognosis of BRAFmut tumors in chemo-naïve metastatic CRC is not explained by associations with poor clinicopathologic prognostic factors, except right-sided primary tumors.

TRIAL REGISTRATION NUMBER

VISNU 1 ClinicalTrials.gov ID: NCT01640405/ VISNU 2 ClinicalTrials.gov ID: NCT01640444.

The heterogeneous clinical and pathological landscapes of metastatic Braf-mutated colorectal cancer

Colorectal cancer (CRC) is a complex and molecularly heterogeneous disease representing one of the most frequent causes of cancer-related death worldwide. About 8–15% of CRCs harbor a mutation in BRAF gene, a proto-oncogene involved in cell proliferation, differentiation and survival through the MAPK signaling cascade. The acquisition of BRAF mutation is an early event in the “serrated” CRC carcinogenetic pathway and is associated with specific and aggressive clinico-pathological and molecular features. Despite that the presence of BRAF mutation is a well-recognized negative prognostic biomarker in metastatic CRC (mCRC), a great heterogeneity in survival outcome characterizes these patients, due to the complex, and still not completely fully elucidated, interactions between the clinical, genetic and epigenetic landscape of BRAF mutations. Because of the great aggressiveness of BRAF-mutated mCRCs, only 60% of patients can receive a second-line chemotherapy; so intensive combined and tailored first-line approach could be a potentially effective strategy, but to minimize the selective pressure of resistant clones and to reduce side effects, a better stratification of patients bearing BRAF mutations is needed.

MSI status is associated with distinct clinicopathological features in BRAF mutation colorectal cancer: A systematic review and meta-analysis

BACKGROUND

Microsatellite stable (MSS) BRAF p.V600E mutation colorectal cancer (BRAF-CRC) has a poor prognosis, whereas microsatellite instability (MSI) in BRAF-CRC is associated with a favorable prognosis. Although usually considered a single clinical entity, the MSI BRAF-CRC subtype shows some distinct characteristics in comparison with the MSS BRAF-CRC subtype.

METHODS

We conducted a meta-analysis to investigate the influence of clinicopathological features on MSI status in BRAF-CRC. We searched publications up to March 2019 from PubMed, Embase, and the Cochrane Library. The effect of MSI status on outcome parameters was assessed using odds ratios (ORs) with 95% confidence intervals (CIs) and fixed- or random-effects models according to the heterogeneity.

RESULTS

After reviewing 2839 reports, 16 eligible studies including 1381 patients with BRAF-CRC met the criteria. The MSI BRAF-CRC subtype was associated with older age, female sex (OR = 1.70; 95% CI = 1.35-2.14; P < 0.00001), proximal tumor location (OR = 5.10; 95% CI = 3.70-7.03; P < 0.00001), early TNM stage (OR = 5.28; 95% CI = 3.93-7.09; P < 0.00001), and poor differentiation (OR = 2.29; 95% CI = 1.60-3.28; P < 0.00001).

CONCLUSIONS

MSI was significantly correlated with distinct favorable clinicopathological characteristics in BRAF-CRC. These results suggest that MSI status should be considered as a stratification factor for better management of the BRAF-CRC.

BRAF Mutation in Colorectal Rhabdoid and Poorly Differentiated Medullary Carcinomas

Colorectal rhabdoid carcinomas (CRbCs) are very rare and aggressive cancers. The BRAF mutation and CpG island methylator phenotype have been reported to be common features of CRbCs. This study reviews the literature about CRbCs and analyzes the clinicopathological and molecular profiles of seven CRbCs characterized by large discohesive cells with abundant eosinophilic cytoplasm, showing hyaline inclusions and large rounded to bean-shaped nuclei. For comparison, we included four poorly differentiated medullary carcinomas (PDMCs) with focal aspects mimicking rhabdoid features. Overall survival was poor in both subsets, with 78% of patients dying of disease within 2–11 months. The main features of CRbCs were: Loss of/reduced SMARCB1/INI expression, intense vimentin immunostaining, and dense neutrophilic infiltration. The PDMCs were positive for pancytokeratin but negative for vimentin and showed moderate peritumoral/intratumoral CD8+ lymphocytes. All PDMCs showed SMARCB1(INI-1) expression. The coexistence of BRAF and TP53 mutations was observed in 80% of CRbCs and PDMCs. PDMCs always showed microsatellite instability and CpG island methylator phenotype (CIMP), while CRbCs were CIMP negative and exhibited microsatellite instability (MSI) in two out of seven cases. CRbCs are characterized by BRAF and TP53 mutations. Loss/reduced expression of nuclear SMARCB1/INI, intense vimentin immunostaining, dense neutrophilic infiltration, and low frequency of CIMP are useful markers to recognize these rare aggressive tumors.

Mutations of key driver genes in colorectal cancer progression and metastasis

The association between mutations of key driver genes and colorectal cancer (CRC) metastasis has been investigated by many studies. However, the results of these studies have been contradictory. Here, we perform a comprehensive analysis to screen key driver genes from the TCGA database and validate the roles of these mutations in CRC metastasis. Using bioinformatics analysis, we identified six key driver genes, namely APC, KRAS, BRAF, PIK3CA, SMAD4 and p53. Through a systematic search, 120 articles published by November 30, 2017, were included, which all showed roles for these gene mutations in CRC metastasis. A meta-analysis showed that KRAS mutations (combined OR 1.18, 95% CI 1.05-1.33) and p53 mutations (combined OR 1.49, 95% CI 1.23-1.80) were associated with CRC metastasis, including lymphatic and distant metastases. Moreover, CRC patients with a KRAS mutation (combined OR 1.29, 95% CI 1.13-1.47), p53 mutation (combined OR 1.35, 95% CI 1.06-1.72) or SMAD4 mutation (combined OR 2.04, 95% CI 1.41-2.95) were at a higher risk of distant metastasis. Subgroup analysis stratified by ethnic populations indicated that the BRAF mutation was related to CRC metastasis (combined OR 1.42, 95% CI 1.18-1.71) and distant metastasis (combined OR 1.51, 95% CI 1.20-1.91) in an Asian population. No significant association was found between mutations of APC or PIK3CA and CRC metastasis. In conclusion, mutations of KRAS, p53, SMAD4 and BRAF play significant roles in CRC metastasis and may be both potential biomarkers of CRC metastasis as well as therapeutic targets.

How the BRAF V600E Mutation Defines a Distinct Subgroup of Colorectal Cancer: Molecular and Clinical Implications

The BRAF oncogene is an integral component of the MAP kinase pathway, and an activating V600E mutation occurs in 15% of sporadic colorectal cancer. This is an early event in serrated pathway tumourigenesis, and the BRAF V600E has been commonly associated with the CpG island methylator phenotype, microsatellite instability (MSI), and a consistent clinical presentation including a proximal location and predilection for elderly females. A proportion of the BRAF mutant lesions remain as microsatellite stable (MSS), and in contrast to the MSI cancers, they have an aggressive phenotype and correlate with poor patient outcomes. Recent studies have found that they have clinical and molecular features of both the BRAF mutant/MSI and the conventional BRAF wild-type cancers and comprise a distinct colorectal cancer subgroup. This review highlights the importance of the BRAF mutation occurring in colorectal cancer stratified for molecular background and discusses its prognostic and clinical significance.

RNF43 and ZNRF3 are commonly altered in serrated pathway colorectal tumorigenesis

Serrated pathway colorectal cancers (CRCs) are characterised by a BRAF mutation and half display microsatellite instability (MSI). The Wnt pathway is commonly upregulated in conventional CRC through APC mutation. By contrast, serrated cancers do not mutate APC. We investigated mutation of the ubiquitin ligases RNF43 and ZNRF3 as alternate mechanism of altering the Wnt signal in serrated colorectal neoplasia. RNF43 was mutated in 47/54(87%) BRAF mutant/MSI and 8/33(24%) BRAF mutant/microsatellite stable cancers compared to only 3/79(4%) BRAF wildtype cancers (p<0.0001). ZNRF3 was mutated in 16/54(30%) BRAF mutant/MSI and 5/33(15%) BRAF mutant/microsatellite stable compared to 0/27 BRAF wild type cancers (p=0.004). An RNF43 frameshift mutation (X659fs) occurred in 80% BRAF mutant/MSI cancers. This high rate was verified in a second series of 25/35(71%) BRAF mutant/MSI cancers. RNF43 and ZNRF3 had lower transcript expression in BRAF mutant compared to BRAF wildtype cancers and less cytoplasmic protein expression in BRAF mutant/MSI compared to other subtypes. Treatment with a porcupine inhibitor reduced RNF43/ZNRF3 mutant colony growth by 50% and synergised with a MEK inhibitor to dramatically reduce growth. This study suggests inactivation of RNF43 and ZNRF3 is important in serrated tumorigenesis and has identified a potential therapeutic strategy for this cancer subtype.

Differentiation of stem cells derived from carious teeth into dopaminergic-like cells

AIM

To investigate whether dental pulp stem cells from carious teeth (DPSCs-CT) can differentiate into functional dopaminergic-like (DAergic) cells and provide an alternative cell source in regenerative medicine.

METHODOLOGY

Dental pulp stem cells from healthy (DPSCs) and carious teeth (DPSCs-CT) were isolated from young donors. Both cell lines were expanded in identical culture conditions and subsequently differentiated towards DAergic-like cells using pre-defined dopaminergic cocktails. The dopaminergic efficiencies were evaluated both at gene and protein as well as at secretome levels.

RESULTS

The efficiency of DPSCs-CT to differentiate into DAergic-like cells was not equivalent to that of DPSCs. This was further reflected in both gene and protein generation whereby key neuronal markers such as nestin, NURR1 and beta-III-tubulin were expressed significantly lower as compared to differentiated DPSCs (P < 0.05). In addition, expressions of transcriptomes related to neurogenesis revealed downregulation of more than 50% of the genes as compared to differentiated DPSC (P < 0.05). Amongst the notable genes were those from the transcription factors family (FLNA, MEF2C, NEUROG2), signalling pathway family (DLL1, Notch1, TGF-β1), neuro-inducer family (BDNF) and cell communication family (APBB1).

CONCLUSIONS

DPSCs-CT were able to differentiate into DAergic-like cells but not as efficiently as DPSCs. As such, prior to use in regenerative medicine, stem cells from any source should be thoroughly investigated beyond conventional benchmarks such as that proposed by the International Society for Cellular Therapy (ISCT).

Embryonal Fyn-associated substrate (EFS) and CASS4: The lesser-known CAS protein family members

The CAS (Crk-associated substrate) adaptor protein family consists of four members: CASS1/BCAR1/p130Cas, CASS2/NEDD9/HEF1/Cas-L, CASS3/EFS/Sin and CASS4/HEPL. While CAS proteins lack enzymatic activity, they contain specific recognition and binding sites for assembly of larger signaling complexes that are essential for cell proliferation, survival, migration, and other processes. All family members are intermediates in integrin-dependent signaling pathways mediated at focal adhesions, and associate with FAK and SRC family kinases to activate downstream effectors regulating the actin cytoskeleton. Most studies of CAS proteins to date have been focused on the first two members, BCAR1 and NEDD9, with altered expression of these proteins now appreciated as influencing disease development and prognosis for cancer and other serious pathological conditions. For these family members, additional mechanisms of action have been defined in receptor tyrosine kinase (RTK) signaling, estrogen receptor signaling or cell cycle progression, involving discrete partner proteins such as SHC, NSP proteins, or AURKA. By contrast, EFS and CASS4 have been less studied, although structure-function analyses indicate they conserve many elements with the better-known family members. Intriguingly, a number of recent studies have implicated these proteins in immune system function, and the pathogenesis of developmental disorders, autoimmune disorders including Crohn's disease, Alzheimer's disease, cancer and other diseases. In this review, we summarize the current understanding of EFS and CASS4 protein function in the context of the larger CAS family group.

Deficient mismatch repair in colorectal cancer: current perspectives on patient management and future directions

Abstract 

Molecular aberrations leading to colorectal cancer are diverse and heterogeneity exists both at a molecular level and in clinical behavior. Defective mismatch repair (dMMR) is a feature of 15% of colorectal cancers. These are hypermutated tumors, mostly right sided and histopathologically elicit a marked immune response. A proportion of these arise due to germline mutation of a mismatch repair gene giving rise to Lynch syndrome, while the majority arise sporadically due to somatic alteration of the MLH1 mismatch repair gene. Although dMMR is associated with an excellent patient prognosis, as tumor stage advances the frequency of dMMR declines and the association with improved prognosis dissipates. It is apparent that dMMR tumors do not represent a unique molecular subset. As the knowledge of the underlying biology evolves, the hope is for individualized therapy that goes well beyond the crude and oversimplified categorization of dMMR versus proficient MMR.

Methylation and expression of the tumour suppressor, PRDM5, in colorectal cancer and polyp subgroups

BACKGROUND

PRDM5 is an epigenetic regulator that has been recognized as an important tumour suppressor gene. Silencing of PRDM5 by promoter hypermethylation has been demonstrated in several cancer types and PRDM5 loss results in upregulation of the Wnt pathway and increased cellular proliferation. PRDM5 has not been extensively investigated in specific subtypes of colorectal cancers. We hypothesized it would be more commonly methylated and inactivated in serrated pathway colorectal cancers that are hallmarked by a BRAF V600E mutation and a methylator phenotype, compared to traditional pathway cancers that are BRAF wild type.

METHODS

Cancer (214 BRAF mutant, 122 BRAF wild type) and polyp (59 serrated polyps, 40 conventional adenomas) cohorts were analysed for PRDM5 promoter methylation using MethyLight technology. PRDM5 protein expression was assessed by immunohistochemistry in cancers and polyps. Mutation of PRDM5 was analysed using cBioPortal's publicly available database.

RESULTS

BRAF mutant cancers had significantly more frequent PRDM5 promoter methylation than BRAF wild type cancers (77/214,36% vs 4/122,3%; p<0.0001). Serrated type polyps had a lower methylation rate than cancers but were more commonly methylated than conventional adenomas (6/59,10% vs 0/40,0%). PRDM5 methylation was associated with advanced stages of presentation (p<0.05) and the methylator phenotype (p=0.03). PRDM5 protein expression was substantially down-regulated in both BRAF mutant and wild type cancer cohorts (92/97,95% and 39/44,89%). The polyp subgroups showed less silencing than the cancers, but similar rates were found between the serrated and conventional polyp cohorts (29/59, 49%; 23/40, 58% respectively). Of 295 colorectal cancers, PRDM5 was mutated in only 6 (2%) cancers which were all BRAF wild type.

CONCLUSIONS

Serrated pathway colorectal cancers demonstrated early and progressive PRDM5 methylation with advancing disease. Interestingly, PRDM5 protein expression was substantially reduced in all polyp types and more so in cancers which also indicates early and increasing PRDM5 down-regulation with disease progression. Methylation may be contributing to gene silencing in a proportion of BRAF mutant cancers, but the large extent of absent protein expression indicates other mechanisms are also responsible for this. These data suggest that PRDM5 is a relevant tumour suppressor gene that is frequently targeted in colorectal tumourigenesis.

Colorectal carcinogenesis-update and perspectives

Colorectal cancer (CRC) is a very common malignancy in the Western World and despite advances in surgery, chemotherapy and screening, it is still the second leading cause of cancer deaths in this part of the world. Numerous factors are found important in the development of CRC including colonocyte metbolism, high risk luminal environment, inflammation, as well as lifestyle factors such as diet, tobacco, and alchohol consumption. In recent years focus has turned towards the genetics and molecular biology of CRC and several interesting and promising correlations and pathways have been discovered. The major genetic pathways of CRC are the Chromosome Instability Pathway representing the pathway of sporadic CRC through the K-ras, APC, and P53 mutations, and the Microsatellite Instability Pathway representing the pathway of hereditary non-polyposis colon cancer through mutations in mismatch repair genes. To identify early cancers, screening programs have been initiated, and the leading strategy has been the use of faecal occult blood testing followed by colonoscopy in positive cases. Regarding the treatment of colorectal cancer, significant advances have been made in the recent decade. The molecular targets of CRC include at least two important cell surface receptors: the epidermal growth factor receptor and the vascular endothelial growth factor receptor. The genetic and molecular knowledge of CRC has widen the scientific and clinical perspectives of diagnosing and treatment. However, despite significant advances in the understanding and treatment of CRC, results from targeted therapy are still not convincing. Future studies will determine the role for this new treatment modality.

Mismatch repair gone awry: Management of Lynch syndrome

The hallmark of Lynch syndrome involves germline mutations of genes important in DNA mismatch repair. Affected family kindreds will have multiple associated malignancies, the most common of which is colorectal adenocarcinoma. Recently, evidence has shown that clinical diagnostic criteria provided by the Amsterdam Criteria and the Bethesda Guidelines must be linked with microsatellite instability testing to correctly diagnose Lynch syndrome. We present a case of metachronous colorectal adenocarcinomas in a patient less than 50 years of age, followed by a discussion of Lynch syndrome, with an emphasis on surveillance and prevention of malignancies.