p16INK4a gene promoter hypermethylation in mucosa as a prognostic factor for patients with colorectal cancer

Methylation-Based Therapies for Colorectal Cancer

Colorectal carcinogenesis (CRC) is caused by the gradual long-term accumulation of both genetic and epigenetic changes. Recently, epigenetic alterations have been included in the classification of the CRC molecular subtype, and this points out their prognostic impact. As epigenetic modifications are reversible, they may represent relevant therapeutic targets. DNA methylation, catalyzed by DNA methyltransferases (DNMTs), regulates gene expression. For many years, the deregulation of DNA methylation has been considered to play a substantial part in CRC etiology and evolution. Despite considerable advances in CRC treatment, patient therapy response persists as limited, and their profit from systemic therapies are often hampered by the introduction of chemoresistance. In addition, inter-individual changes in therapy response in CRC patients can arise from their specific (epi)genetic compositions. In this review article, we summarize the options of CRC treatment based on DNA methylation status for their predictive value. This review also includes the therapy outcomes based on the patient's methylation status in CRC patients. In addition, the current challenge of research is to develop therapeutic inhibitors of DNMT. Based on the essential role of DNA methylation in CRC development, the application of DNMT inhibitors was recently proposed for the treatment of CRC patients, especially in patients with DNA hypermethylation.

Study of p16 promoter methylation in Egyptian colorectal cancer patients

Many tumor-suppressor genes contain CpG islands in their promoter regions which raised the necessity of investigating the role of methylation in silencing these genes. We examined p16 methylation as a potential biomarker in the peripheral blood of colorectal cancer (CRC) patients. Using methylation-specific polymerase chain reaction method, the methylation status of p16 was investigated in the tumor tissue and blood of 65 CRC patients and blood samples from 70 healthy control individuals. Also, the relationship between p16 methylation level and the clinical-pathological findings in CRC was evaluated. The frequency of blood p16 methylation in CRC cases was significantly higher than in control (P = 0.0001). The sensitivity and specificity of p16 methylation in diagnosing CRC was 55.38% and 98.5%, respectively, with 77.7% diagnostic accuracy. There was significant association between p16 methylation and age, sex, Dukes staging, lymph node involvement, and carcinoembryonic antigen levels. Our study revealed that p16 promoter methylation could be considered as both potential diagnostic and prognostic biomarker of CRC.

Prognostic DNA methylation markers for sporadic colorectal cancer: a systematic review

Background

Biomarkers that can predict the prognosis of colorectal cancer (CRC) patients and that can stratify high-risk early stage patients from low-risk early stage patients are urgently needed for better management of CRC. During the last decades, a large variety of prognostic DNA methylation markers has been published in the literature. However, to date, none of these markers are used in clinical practice.

Methods

To obtain an overview of the number of published prognostic methylation markers for CRC, the number of markers that was validated independently, and the current level of evidence (LoE), we conducted a systematic review of PubMed, EMBASE, and MEDLINE. In addition, we scored studies based on the REMARK guidelines that were established in order to attain more transparency and complete reporting of prognostic biomarker studies. Eighty-three studies reporting on 123 methylation markers fulfilled the study entry criteria and were scored according to REMARK.

Results

Sixty-three studies investigated single methylation markers, whereas 20 studies reported combinations of methylation markers. We observed substantial variation regarding the reporting of sample sizes and patient characteristics, statistical analyses, and methodology. The median (range) REMARK score for the studies was 10.7 points (4.5 to 17.5) out of a maximum of 20 possible points. The median REMARK score was lower in studies, which reported a p value below 0.05 versus those, which did not (p = 0.005). A borderline statistically significant association was observed between the reported p value of the survival analysis and the size of the study population (p = 0.051). Only 23 out of 123 markers (17%) were investigated in two or more study series. For 12 markers, and two multimarker panels, consistent results were reported in two or more study series. For four markers, the current LoE is level II, for all other markers, the LoE is lower.

Conclusion

This systematic review reflects that adequate reporting according to REMARK and validation of prognostic methylation markers is absent in the majority of CRC methylation marker studies. However, this systematic review provides a comprehensive overview of published prognostic methylation markers for CRC and highlights the most promising markers that have been published in the last two decades.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0461-8) contains supplementary material, which is available to authorized users.

The role of cell-free DNA in predicting colorectal cancer prognosis

Colorectal cancer is a cancer of the digestive system with poor prognosis. Cell-free DNA has received much attention with its unique predominance, especially in colorectal cancer. Areas covered: This study has summarized recent advancements and challenges regarding cell-free DNA in predicting CRC prognosis. Furthermore, the authors make predictions on the potential developments concerning cell-free DNA in future prognosis prediction techniques. Expert commentary: Cell-free DNA has the value of predicting CRC prognosis as an important biomarke. Further clinical trials should be performed to promote translating cell-free DNA into clinical applications.

Differential Expression of ADAM23, CDKN2A (P16), MMP14 and VIM Associated with Giant Cell Tumor of Bone

Though benign, giant cell tumor of bone (GCTB) can become aggressive and can exhibit a high mitotic rate, necrosis and rarely vascular invasion and metastasis. GCTB has unique histologic characteristics, a high rate of multinucleated cells, a variable and unpredictable growth potential and uncertain biological behavior. In this study, we sought to identify genes differentially expressed in GCTB, thus building a molecular profile of this tumor. We performed quantitative real-time polymerase chain reaction (qPCR), immunohistochemistry and analyses of methylation to identify genes that are putatively associated with GCTB. The expression of the ADAM23 and CDKN2A genes was decreased in GCTB samples compared to normal bone tissue, measured by qPCR. Additionally, a high hypermethylation frequency of the promoter regions of ADAM23 and CDKN2A in GCTB was observed. The expression of the MAP2K3, MMP14, TIMP2 and VIM genes was significantly higher in GCTB than in normal bone tissue, a fact that was confirmed by qPCR and immunohistochemistry. The set of genes identified here furthers our understanding of the molecular basis of GCTB.

DNA methylation and expression of the folate transporter genes in colorectal cancer

Folate has a central role in the cell metabolism. This study aims to explore the DNA methylation pattern of the folate transporter genes FOLR1, PCFT, and RFC1 as well as the corresponding protein expressions in colorectal cancer (CRC) tissue and adjacent non-cancerous mucosa (ANCM). Our results showed statistically significant differences in the DNA-methylated fraction of all three genes at several gene regions; we identified three differentially methylated CpG sites in the FOLR1 gene, five CpG sites in the PCFT gene, and six CpG sites in the RFC1 gene. There was a pronounced expression of the FRα and RFC proteins in both the CRC and ANCM tissues, though the expression was attenuated in cancer compared to the paired ANCM tissues. The PCFT protein was undetectable or expressed at a very low level in both tissue types. Higher methylated fractions of the CpG sites 3-5 in the RFC1 gene were associated with a lower protein expression, suggestive of epigenetic regulation by DNA methylation of the RFC1 gene in the colorectal cancer. Our results did not show any association between the RFC and FRα protein expression and tumor stage, TNM classification, or tumor location. In conclusion, this is the first study to simultaneously evaluate both DNA methylation and protein expression of all three folate transporter genes, FOLR1, PCFT, and RFC1, in colorectal cancer. The results encourage further investigation into the possible prognostic implications of folate transporter expression and DNA methylation.

Relationships between p16 gene promoter methylation and clinicopathologic features of colorectal cancer: a meta-analysis of 27 cohort studies

Many existing studies have demonstrated that p16 promoter methylation might be correlated with the clinicopathologic features of colorectal cancer (CRC), but individually published results are inconclusive. This meta-analysis aimed to derive a more precise estimation of the relationships between p16 promoter methylation and the clinicopathologic features of CRC. We searched the CISCOM, CINAHL, Web of Science, PubMed, Google Scholar, EBSCO, Cochrane Library, and CBM databases from inception through August 1, 2013. Meta-analysis was performed using the STATA 12.0 software. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated under fixed- or random-effects models. Twenty-seven clinical cohort studies were included with a total of 3311 CRC patients. Our meta-analysis results revealed that p16 promoter methylation was associated with pathological characteristics of CRC (tumor, nodes, metastasis stage: OR=1.55, 95% CI: 1.14-2.13, p=0.006; lymph node metastasis: OR=2.40, 95% CI: 1.37-4.19, p=0.002; histologic grade: OR=2.72, 95% CI: 1.63-4.54, p<0.001; Dukes stage: OR=2.06, 95% CI: 1.57-2.71, p=0.002; tumor size: OR=1.99, 95% CI: 1.03-3.85, p=0.041; location: OR=2.49, 95% CI: 1.95-3.18, p<0.001, respectively). Subgroup analysis by ethnicity suggested that there were also significant correlations between p16 gene promoter methylation and pathological characteristics of CRC among both Caucasian and Asian populations (all p<0.05). Our meta-analysis suggests that promoter methylation of the p16 gene may be strongly correlated with the clinicopathologic features of CRC. Thus, p16 gene promoter methylation may be a potential biomarker for CRC.

The specific methylation characteristics of cancer related genes in Chinese colorectal cancer patients

Aberrant DNA methylation at CpG islands has been implicated as a critical player in colorectal cancer (CRC). However, its biological role and clinical significance in carcinogenesis have not been clearly clarified in Chinese CRC patients. In order to examine the methylation status of cancer-related genes in CRC progression, 184 tumor tissues were collected from Chinese patients diagnosed with CRC during 2008-2011. Promoter methylation was assessed by combined bisulphite-restriction analysis, methylation-specific PCR, and bisulphite sequencing PCR . The relationship between the gene promoter methylation status and clinicopathological factors/CRC mortality was examined by using the chi-square test/Cox-proportional hazards models. Promoter hypermethylation of MLH1, p16, SFRP2, PHD3, KLOTHO, and IGFBP7 was observed in 1.6, 10.9, 97.3, 44.0, 59.8, and 88.6 % of CRC samples, respectively. KLOTHO promoter methylation reduced with age (P = 0.018) whereas p16 promoter methylation increased with age (P = 0.044) and was more frequent among males (P = 0.017). Tumor tissues (73.9 %) had concurrent methylation of two or more genes, with the most frequent combination as KLOTHO and IGFBP7 (53.8 %). Concurrent methylation of KLOTHO and IGFBP7 occurred more frequently among patients less than 70 years old (P = 0.035) and those with poor differentiation (P = 0.024). CRC-specific mortality was not associated with promoter methylation and clinicopathological features except for age (P = 0.038; risk ratio (RR), 1.96; 95 % confidence interval (CI), 1.04-3.70) and TNM stage (P = 0.034; RR, 3.47; 95 % CI, 1.10-10.92). Methylation frequencies of MLH1, p16, PHD3, KLOTHO, and IGFBP7 in CRC tissues were significantly higher than that in the paired normal tissues, while promoter hypermethylation of SFRP2 was widespread in normal tissues. In conclusion, we suggest that methylation of some genes (MLH1, PHD3, KLOTHO, p16, and IGFBP7) is important in CRC progression whereas SFRP2 methylation is unlikely to contribute to CRC development in Chinese patients. Besides, by identifying the characteristics of concordant methylation, we confirm the multifactorial nature of tumor progression.

Screening for differentially methylated genes among human colorectal cancer tissues and normal mucosa by microarray chip

High density DNA methylation microarrays were used to study the differences of gene methylation level in six pairs of colorectal cancer (CRC) and adjacent normal mucosa. We analyzed the profile of methylated genes by NimbleGen Microarray and the biologic functions by NIH-NAVID. In addition, preliminary validation studies were done in six pairs of samples by MSP (methylation-specific PCR). A total of 4,644 genes had a difference in methylation levels. Among them 2,296 were hypermethylated (log2ratio > 1), 2,348 genes were hypomethylated (log2ratio < -1), in which 293 hypermethylated and 313 hypomethylated genes were unmapped according to the NIH-NAVID. All these genes were randomly distributed on all the chromosomes. However, chromosome 1 contained the most of the hypermethylated genes (232 genes), followed by chromosome 19 (149 genes), chromosome 11 (144 genes), chromosome 2 (141 genes), chromosomes 3 (127 genes). Through the analysis of the statistics, There were 2 hypermethylated/3 hypomethylated genes involved in six pairs of samples simultaneously, followed by 10/14 in five samples, 34/37 in four samples, 101/113 in three samples, 341/377 in two samples, 1,808/1,804 in one sample. According to gene ontology analysis, some physiological processes play important roles in the cell division and the development of tumor, such as apoptosis, DNA repair, immune, cell cycle, cell cycle checkpoint, cell adhesion and invasion etc. Through Preliminary validation, there were two genes (St3gal6, Opcml) in thirty top-ranking genes shown hypermethylated in six pairs of CRC and adjacent normal mucosa.

CONCLUSIONS

High density DNA methylation microarrays is an effective method for screening aberrantly methylated genes in CRC. The methylated genes should be further studied for diagnostic or prognostic markers for CRC.

DNA methylation of the p14ARF, RASSF1A and APC1A genes as an independent prognostic factor in colorectal cancer patients

We quantitated the methylated fraction of CpG sites in the promoter regions of O⁶-MGMT, p14^ARF, p16^INK4a, RASSF1A and APC1A in tumor tissue from patients with colorectal cancer (CRC) in order to determine if promoter hypermethylation of any of these genes predicts survival. DNA was isolated from 111 primary CRC and 46 matched normal colorectal mucosa samples from the same patients, obtained at primary surgery and DNA methylation was examined by Pyrosequencing^®. Follow-up time was up to 20 years. Patients showed partial promoter methylation in the following frequencies: O⁶-MGMT, 34%; p14^ARF, 29%; p16^INK4a, 28%; RASSF1A, 14%; and APC1A, 27%. Normal mucosa was always unmethylated. CRC patients with methylated p14^ARF gene promoter had significantly worse prognosis (p=0.036), whereas those with methylated O⁶-MGMT had significantly better prognosis through the first 60 months post-treatment (RR 0.36; p=0.023). Methylation of one or more of the genes from the set p14^ARF, RASSF1A and APC1A, was significantly (p= 0.021) associated with worse prognosis even adjusting for tumor stage and differentiation (RR 2.2, p=0.037). Thus, DNA methylation of the p14^ARF, RASSF1A and APC1A genes, diagnosed by Pyrosequencing, defines a poor prognosis subset of CRC patients independently of both tumor stage and differentiation. O⁶-MGMT methylation may play a protective role.

p37δ is a new isoform of PI3K p110δ that increases cell proliferation and is overexpressed in tumors

The phosphatidylinositol 3-kinases (PI3Ks) regulate cell growth, proliferation and survival, and are frequently affected in human cancer. PI3K is composed of a catalytic subunit, p110, and a regulatory subunit, p85. The PI3K catalytic subunit p110δ is encoded by PIK3CD and contains p85- and RAS-binding domains, and a kinase domain. Here we present an alternatively spliced PIK3CD transcript encoding a previously unknown protein, p37δ, and demonstrate that this protein is expressed in human ovarian and colorectal tumors. p37δ retains the p85-binding domain and a fraction of the RAS-binding domain, lacks the catalytic domain, and has a unique carboxyl-terminal region. In contrast to p110δ, which stabilizes p85, p37δ promoted p85 sequestering. Despite the truncated RAS-binding domain, p37δ bound to RAS and we found a strong positive correlation between the protein levels of p37δ and RAS. Overexpressing p37δ, but not p110δ, increased the proliferation and invasive properties of HEK-293 cells and mouse embryonic fibroblasts. Cells overexpressing p37δ showed a quicker phosphorylation response of AKT and ERK1/2 following serum stimulation. Ubiquitous expression of human p37δ in the fruit fly increased body size, DNA content and phosphorylated ERK1/2 levels. Thus, p37δ appears to be a new tumor-specific isoform of p110δ with growth-promoting properties.

A study of aspects on gender and prognosis in synchronous colorectal cancer

AIM

To assess differences in demography, pathology and prognosis with tumor multiplicity in colorectal cancer.

METHOD

A retrospective single centre study of all patients surgically treated for a colorectal cancer during 1999-2008 (n = 2524). Patient characteristics, pathology and follow-up data were retrieved. Survival was assessed by overall and cancer specific survival.

RESULTS

60 (2.4%) patients had a synchronous cancer (SC), associated with right colon, higher age, more assessed lymph nodes but a lower frequency of stage III/IV disease (42% vs. 52%). There was no overall prognostic difference between single or multiple cancer patients but females with SC had better survival than corresponding males (P < 0.046).

CONCLUSION

The incidence of synchronous cancers was 2.4% with the second cancer often located in right colon. The SC patients were older than single tumor patients, had a lower frequency of stage III/IV disease and the females with SC had a better survival prognosis than corresponding males.

Aberrant methylation of hMLH1 and p16INK4a in Tunisian patients with sporadic colorectal adenocarcinoma

The methylation of CpG islands in the promoters is associated with loss of protein via repression of gene transcription. Several studies have demonstrated that tumour suppressor and DNA repair genes are often aberrantly hypermethylated in colorectal cancer. The present study was conducted to examine whether the methylation profile of p16INK4a and hMLH1 (human mutL homologue 1) promoters was associated with clinical features and patients’ survival in CRC (colorectal carcinoma). Aberrant methylation of p16INK4a and hMLH1 promoters was found in 47.2 and 53.4% of tumours respectively. For adjacent non-tumoral mucosa, p16INK4a was fully unmethylated in 30% of the cases, whereas hMLH1 was predominantly unmethylated (76%). Methylation of p16INK4a correlated with gender and tumour size (P=0.005 and 0.035 respectively), whereas those of hMLH1 significantly correlated with overall survival (P log rank = 0.007). Concomitant methylation of p16INK4a and hMLH1 was associated with TNM (tumour, lymph node and metastases) stage and tumour size (P=0.024 and 0.021 respectively). Our data show that loss of hMLH1 expression through aberrant methylation could be used as a marker of poor prognosis in CRC.

Genetics, cytogenetics, and epigenetics of colorectal cancer

Most of the colorectal cancer (CRC) cases are sporadic, only 25% of the patients have a family history of the disease, and major genes causing syndromes predisposing to CRC only account for 5-6% of the total cases. The following subtypes can be recognized: MIN (microsatellite instability), CIN (chromosomal instability), and CIMP (CpG island methylator phenotype). CIN occurs in 80-85% of CRC. Chromosomal instability proceeds through two major mechanisms, missegregation that results in aneuploidy through the gain or loss of whole chromosomes, and unbalanced structural rearrangements that lead to the loss and/or gain of chromosomal regions. The loss of heterozygosity that occur in the first phases of the CRC cancerogenesis (in particular for the genes on 18q) as well as the alteration of methylation pattern of multiple key genes can drive the development of colorectal cancer by facilitating the acquisition of multiple tumor-associated mutations and the instability phenotype.

Prognostic significance of CDKN2A (p16) promoter methylation and loss of expression in 902 colorectal cancers: Cohort study and literature review

A cyclin-dependent kinase inhibitor CDKN2A (p16/Ink4a) is a tumor suppressor and upregulated in cellular senescence. CDKN2A promoter methylation and gene silencing are associated with the CpG island methylator phenotype (CIMP) in colon cancer. However, prognostic significance of CDKN2A methylation or loss of CDKN2A (p16) expression independent of CIMP status remains uncertain. Using a database of 902 colorectal cancers in 2 independent cohort studies (the Nurses' Health Study and the Health Professionals Follow-up Study), we quantified CDKN2A promoter methylation and detected hypermethylation in 269 tumors (30%). By immunohistochemistry, we detected loss of CDKN2A (p16) expression in 25% (200/804) of tumors. We analyzed for LINE-1 hypomethylation and hypermethylation at 7 CIMP-specific CpG islands (CACNA1G, CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1); microsatellite instability (MSI); KRAS, BRAF and PIK3CA mutations; and expression of TP53 (p53), CTNNB1 (β-catenin), CDKN1A (p21), CDKN1B (p27), CCND1 (cyclin D1), FASN (fatty acid synthase) and PTGS2 (cyclooxygenase-2). CDKN2A promoter methylation and loss of CDKN2A (p16) were associated with shorter overall survival in univariate Cox regression analysis [hazard ratio (HR): 1.36, 95% CI: 1.10-1.66, p = 0.0036 for CDKN2A methylation; HR: 1.30, 95% CI: 1.03-1.63, p = 0.026 for CDKN2A (p16) loss] but not in multivariate analysis that adjusted for clinical and tumor variables, including CIMP, MSI and LINE-1 methylation. Neither CDKN2A promoter methylation nor loss of CDKN2A (p16) was associated with colorectal cancer-specific mortality in uni- or multivariate analysis. Despite its well-established role in carcinogenesis, CDKN2A (p16) promoter methylation or loss of expression in colorectal cancer is not independently associated with patient prognosis.

Expression of p16 in lymph node metastases of adjuvantly treated stage III colorectal cancer patients identifies poor prognostic subgroups: a retrospective analysis of biomarkers in matched primary tumor and lymph node metastases

BACKGROUND

The objective of identifying protein biomarkers for patients with stage III and IV colorectal cancer is to improve risk stratification and, thus, to identify patients in the postoperative setting who may benefit from more targeted treatment. The objective of the current study was to determine the prognostic value of 19 protein markers assessed in primary tumors and matched lymph node (LN) metastases from patients with stage III and IV colorectal cancer.

METHODS

Matched primary tumors and LN metastases from 82 patients with stage III and IV colorectal cancer were mounted onto a multiple-punch tissue microarray and were stained for 19 protein markers involved in tumor progression (β-catenin, E-cadherin, epidermal growth factor receptor, phosphorylated extracellular signal-regulated kinase [pERK], receptor for hyaluronic acid-mediated motility, phosphorylated protein kinase B, p21, p16, B-cell lymphoma 2, Ki67, apoptotic protease activating factor 1, mammalian sterile 20-like kinase 1, Raf kinase inhibitor protein, vascular endothelial growth factor, ephrin type-B receptor 2, matrix metalloproteinase 7, laminin5γ2, mucin 1 [MUC1], and caudal-related homeobox 2). The prognostic effects of biomarkers in both primary tumor and positive LNs were assessed.

RESULTS

MUC1, pERK and p16 in LN (P=.002, P=.014, and P=.002, respectively) had independent prognostic value. In patients with stage III disease who received adjuvant treatment, negative p16 expression was associated with highly unfavorable outcomes overall (hazard ratio [HR], 0.26; 95% confidence interval [CI], 0.1-0.6; P=.005) when the analysis was stratified by pathologic tumor classification (HR, 0.25; 95% CI, 0.1-0.7; P=.005), age (HR, 0.23; 95% CI, 0.1-0.6; P=.004), and LN ratio (HR, 0.26; 95% CI, 0.1-0.7; P=.007); and, in multivariate analysis, it was associated with performance status and the receipt of folic acid treatment (HR, 0.29; 95% CI, 0.09-0.89; P=.03).

CONCLUSIONS

The loss of p16 in LN metastases contributed to adverse outcomes in adjuvantly treated patients with stage III colorectal cancer independent of pathologic tumor classification, age, LN ratio, performance status, or folic acid treatment. The current results support the investigation of p16 as a prognostic and potential predictive biomarker for future randomized trials of patients with stage III colorectal cancer.

Epigenomics in cancer management

The identification of all epigenetic modifications implicated in gene expression is the next step for a better understanding of human biology in both normal and pathological states. This field is referred to as epigenomics, and it is defined as epigenetic changes (ie, DNA methylation, histone modifications and regulation by noncoding RNAs such as microRNAs) on a genomic scale rather than a single gene. Epigenetics modulate the structure of the chromatin, thereby affecting the transcription of genes in the genome. Different studies have already identified changes in epigenetic modifications in a few genes in specific pathways in cancers. Based on these epigenetic changes, drugs against different types of tumors were developed, which mainly target epimutations in the genome. Examples include DNA methylation inhibitors, histone modification inhibitors, and small molecules that target chromatin-remodeling proteins. However, these drugs are not specific, and side effects are a major problem; therefore, new DNA sequencing technologies combined with epigenomic tools have the potential to identify novel biomarkers and better molecular targets to treat cancers. The purpose of this review is to discuss current and emerging epigenomic tools and to address how these new technologies may impact the future of cancer management.

MTHFR, MTR, and MTRR polymorphisms in relation to p16INK4A hypermethylation in mucosa of patients with colorectal cancer

We recently analyzed the hypermethylation status of the p16INK4a (p16) gene promoter in normal-appearing mucosa obtained from patients with colorectal cancer. Hypermethylation of p16 was associated with reduced survival of these patients. In the present study, germ line polymorphisms in the folate- and methyl-associated genes, methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR) and methionine synthase reductase (MTRR), were analyzed in the same patient cohort to find a possible link between these genetic variants and p16 hypermethylation. Genomic DNA was extracted from blood of patients (n = 181) and controls (n = 300). Genotype analyses were run on an ABI PRISM(®) 7900HT sequence-detection system (Applied Biosystems), using real-time polymerase chain reaction and TaqMan chemistry. The results showed that the genotype distributions of the patient and control groups were similar. No significant differences in cancer-specific or disease-free survival of stage I-III patients according to polymorphic variants were detected, nor were any differences in cancer-specific or disease-free survival detected when patients were subgrouped according to the MTHFR or MTR genotype groups and dichotomized by p16 hypermethylation status in mucosa. However, patients with the MTRR 66 AA/AG genotypes were found to have a significantly worse cancer-specific survival when the mucosa were positive, compared with negative, for p16 hypermethylation (hazard ratio 2.7; 95% confidence interval 1.2-6.4; P = 0.023). In contrast, there was no difference in survival among patients with the MTRR 66 GG genotype stratified by p16 hypermethylation status. These results indicate a relationship between genetic germ-line variants of the MTRR gene and p16 hypermethylation in mucosa, which may affect the clinical outcome of patients with colorectal cancer.

MTHFR, MTR, and MTRR polymorphisms in relation to p16INK4A hypermethylation in mucosa of patients with colorectal cancer

We recently analyzed the hypermethylation status of the p16INK4a (p16) gene promoter in normal-appearing mucosa obtained from patients with colorectal cancer. Hypermethylation of p16 was associated with reduced survival of these patients. In the present study, germ line polymorphisms in the folate- and methyl-associated genes, methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR) and methionine synthase reductase (MTRR), were analyzed in the same patient cohort to find a possible link between these genetic variants and p16 hypermethylation. Genomic DNA was extracted from blood of patients (n = 181) and controls (n = 300). Genotype analyses were run on an ABI PRISM(®) 7900HT sequence-detection system (Applied Biosystems), using real-time polymerase chain reaction and TaqMan chemistry. The results showed that the genotype distributions of the patient and control groups were similar. No significant differences in cancer-specific or disease-free survival of stage I-III patients according to polymorphic variants were detected, nor were any differences in cancer-specific or disease-free survival detected when patients were subgrouped according to the MTHFR or MTR genotype groups and dichotomized by p16 hypermethylation status in mucosa. However, patients with the MTRR 66 AA/AG genotypes were found to have a significantly worse cancer-specific survival when the mucosa were positive, compared with negative, for p16 hypermethylation (hazard ratio 2.7; 95% confidence interval 1.2-6.4; P = 0.023). In contrast, there was no difference in survival among patients with the MTRR 66 GG genotype stratified by p16 hypermethylation status. These results indicate a relationship between genetic germ-line variants of the MTRR gene and p16 hypermethylation in mucosa, which may affect the clinical outcome of patients with colorectal cancer.