Methylated APC and GSTP1 genes in serum DNA correlate with the presence of circulating blood tumor cells and are associated with a more aggressive and advanced breast cancer disease

The assessment of circulating cell-free DNA as a diagnostic tool for breast cancer: an updated systematic review and meta-analysis of quantitative and qualitative ssays

OBJECTIVES

This updated meta-analysis aimed to assess the diagnostic accuracy of circulating cell-free DNA (cfDNA) in breast cancer (BC).

CONTENT

An extensive systematic search was performed in PubMed, Scopus, Embase, and Science Direct databases to retrieve all related literature. Various diagnostic estimates, including sensitivity (SE), specificity (SP), likelihood ratios (LRs), diagnostic odds ratio (DOR), and area under the curve (AUC) of summary receiver operating characteristic (sROC) curve, were also calculated using bivariate linear mixed models.

SUMMARY

In this meta-analysis, 57 unique articles (130 assays) on 4246 BC patients and 2,952 controls, were enrolled. For quantitative approaches, pooled SE, SP, PLR, NLR, DOR, and AUC were obtained as 0.80, 0.88, 6.7, 0.23, 29, and 0.91, respectively. Moreover, for qualitative approaches, pooled SE and SP for diagnostic performance were obtained as 0.36 and 0.98, respectively. In addition, PLR was 14.9 and NLR was 0.66. As well, the combined DOR was 23, and the AUC was 0.79.

OUTLOOK

Regardless of promising SE and SP, analysis of LRs suggested that quantitative assays are not robust enough neither for BC confirmation nor for its exclusion. On the other hand, qualitative assays showed satisfying performance only for confirming the diagnosis of BC, but not for its exclusion. Furthermore, qualitative cfDNA assays showed a better diagnostic performance in patients at the advanced stage of cancer, which represented no remarkable clinical significance as a biomarker for early detection.

Role of DNA Methylation in the Resistance to Therapy in Solid Tumors

Despite the recent advances in chemotherapeutic treatments against cancer, some types of highly aggressive and invasive cancer develop drug resistance against conventional therapies, which continues to be a major problem in the fight against cancer. In recent years, studies of alterations of DNA methylome have given us a better understanding of the role of DNA methylation in the development of tumors. DNA methylation (DNAm) is an epigenetic change that promotes the covalent transfer of methyl groups to DNA. This process suppresses gene expression through the modulation of the transcription machinery access to the chromatin or through the recruitment of methyl binding proteins. DNAm is regulated mainly by DNA methyltransferases. Aberrant DNAm contributes to tumor progression, metastasis, and resistance to current anti-tumoral therapies. Aberrant DNAm may occur through hypermethylation in the promoter regions of tumor suppressor genes, which leads to their silencing, while hypomethylation in the promoter regions of oncogenes can activate them. In this review, we discuss the impact of dysregulated methylation in certain genes, which impact signaling pathways associated with apoptosis avoidance, metastasis, and resistance to therapy. The analysis of methylome has revealed patterns of global methylation, which regulate important signaling pathways involved in therapy resistance in different cancer types, such as breast, colon, and lung cancer, among other solid tumors. This analysis has provided gene-expression signatures of methylated region-specific DNA that can be used to predict the treatment outcome in response to anti-cancer therapy. Additionally, changes in cancer methylome have been associated with the acquisition of drug resistance. We also review treatments with demethylating agents that, in combination with standard therapies, seem to be encouraging, as tumors that are in early stages can be successfully treated. On the other hand, tumors that are in advanced stages can be treated with these combination schemes, which could sensitize tumor cells that are resistant to the therapy. We propose that rational strategies, which combine specific demethylating agents with conventional treatment, may improve overall survival in cancer patients.

Circulating Tumor Cells in Metastatic Breast Cancer: From Genome Instability to Metastasis

The emergence of clinical resistance in repeatedly treated cancers extends from the primary tumor's capability to exploit genome instability to adapt, escape, and progress. Triple negative breast cancer serves as a good example of such a response demonstrating poor clinical outcome due to a high rate of cellular heterogeneity resulting in metastatic relapse. The capability to effectively track the emergence of therapeutic resistance in real-time and adapt the clinical response is the holy grail for precision medicine and has yet to be realized. In this review we present liquid biopsy using CTCs and ctDNA as a potential replacement and/or addition to the current diagnostic tests to deliver personalized therapies to patients with advanced breast cancer. We outline current uses of liquid biopsy in the metastatic breast cancer setting and discuss their limitations. In addition, we provide a detailed overview of common genome instability events in patients with metastatic breast cancer and how these can be tracked using liquid biopsy.

Epigenetics of Circulating Tumor Cells in Breast Cancer

Liquid biopsy based on the analysis of circulating tumor cells (CTCs) has emerged as an important field of research. Molecular characterization of CTCs can provide insights into cancer biology and biomarkers for the clinic, representing a non-invasive powerful tool for monitoring breast cancer metastasis and predict the therapeutic response. Epigenetic mechanisms play a key role in the control of gene expression and their alteration contributes to cancer development and progression. These epigenetic modifications in CTCs have been described mainly related to modifications of the DNA methylation pattern and changes in the expression profile of noncoding RNAs. Here we summarize the recent findings on the epigenetic characterization of CTCs in breast cancer and their clinical value as tumor biomarkers, and discuss challenges and opportunities in this field.

Circulating tumor DNA RASSF1 methylation for predicting cancer risk: a diagnostic meta-analysis

Aim: We conducted a meta-analysis to assess diagnostic accuracy of circulating tumor DNA RASSF1 methylation in cancer. Materials & methods: Studies were searched from PubMed, Embase, Web of Science and China National Knowledge Infrastructure databases for articles published until December 2018. The sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio and summary receiver operating characteristic were used to assess the diagnostic value, and MethHC database was used for verification. Results: 13 studies with 1237 subjects and 676 cancer patients were enrolled. The area under curve was 0.80 (95% CI: 0.76-0.83), the pooled sensitivity was 0.35 (95% CI: 0.31-0.39) and the specificity was 0.97 (95% CI: 0.95-0.98). Verification by MethHC database was almost consistent with the result of meta-analysis. Conclusion: Circulating tumor DNA RASSF1 methylation is a potential biomarker for predicting cancer.

FBX8 degrades GSTP1 through ubiquitination to suppress colorectal cancer progression

F-box only protein 8 (FBX8), as a critical component of the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligases, has been associated with several malignancies through interacting with a member of proteins. However, the substrates of FBX8 for destruction in the progression of colorectal carcinoma (CRC) need to be explored. Here, we show that loss of FBX8 accelerates chemical-induced colon tumorigenesis. FBX8 directly targets GSTP1 for ubiquitin-mediated proteasome degradation in CRC. GSTP1 promotes the proliferation, invasion, and metastasis of CRC cells. Furthermore, GSTP1 is upregulated in CRC tissue samples and predicts poor prognosis of CRC patients. The inactivation of FBX8 negatively correlated with increased levels and stability of GSTP1 in clinical CRC tissues and FBX8 knockout transgenic mice. These findings identify a novel ubiquitination pathway as FBX8-GSTP1 axis that regulates the progression of CRC, which might be a potential prognostic biomarker for CRC patients.

GSTP1 methylation in cancer: a liquid biopsy biomarker?

The coding region of GSTP1 gene is preceded by a large CpG-rich region that is frequently affected by methylation. In many cancer types, GSTP1 is affected by hypermethylation and, as a consequence, it has a low expression. The aim of this review is to give an overview on GSTP1 methylation studies with a special focus on liquid biopsy, thus to summarize methods, results, sample types, different diseases, to have a complete information regarding this promising epigenetic biomarker. We used all the most valuable scientific search engines (PubMed, Medline, Scopus and Web of Science) searching the following keywords: GSTP1, methylation, cancer, urine, serum, plasma and blood. GSTP1 is a largely investigated tissue biomarker in several malignancies such as prostate, breast, lung and hepatocellular carcinoma with good performances especially for diagnostic purposes. As a liquid biopsy biomarker, it has been mainly investigated in prostate cancer (PCa) where it showed a high specificity but a low sensitivity; thus, it is recommended in combination with other biomarkers. Despite the large number of published papers and the promising results, GSTP1 has not yet entered the clinical practice even for PCa diagnosis. For this reason, further large and prospective studies are needed to validate this assay.

Liquid biopsy prediction of axillary lymph node metastasis, cancer recurrence, and patient survival in breast cancer: A meta-analysis

BACKGROUND

Liquid biopsies using circulating tumor DNA (ctDNA) and cell-free DNA (cfDNA) have been developed for early cancer detection and patient monitoring. To investigate the clinical usefulness of ctDNA aberrations and cfDNA levels in patients with breast cancer (BC), we conducted a meta-analysis of 69 published studies on 5736 patients with BC.

METHODS

The relevant publications were identified by searching PubMed and Embase databases. The effect sizes of outcome parameters were pooled using a random-effects model.

RESULTS

The ctDNA mutation rates of TP53, PIK3CA, and ESR1 were approximately 38%, 27%, and 32%, respectively. High levels of cfDNA were associated with BCs rather than with healthy controls. However, these detection rates were not satisfactory for BC screening. Although the precise mechanisms have been unknown, high cfDNA levels were significantly associated with axillary lymph node metastasis (odds ratio [OR] = 2.148, P = .030). The ctDNA mutations were significantly associated with cancer recurrence (OR = 3.793, P < .001), short disease-free survival (univariate hazard ratio [HR] = 5.180, P = .026; multivariate HR = 3.605, P = .001), and progression-free survival (HR = 1.311, P = .013) rates, and poor overall survival outcomes (HR = 2.425, P = .007).

CONCLUSION

This meta-analysis demonstrates that ctDNA mutation status predicts disease recurrence and unfavorable survival outcomes, while cfDNA levels can be predictive of axillary lymph node metastasis in patients with BC.

Quantitative assessment of the association between APC promoter methylation and breast cancer

Adenomatous polyposis coli (APC) is an important tumor suppressor gene in breast cancer. However, there were inconsistent conclusions in the association between APC promoter methylation and breast cancer. Hence, we conducted a meta-analysis to quantitatively assess the clinicopathological significance and diagnosis role of APC methylation in breast cancer. In total, 3172 samples from 29 studies were performed in this study. The odds ratio (OR) of APC methylation was 5.92 (95% CI = 3.16–11.07) in breast cancer cases compared to controls,. The APC promoter methylation was associated with cancer stage (OR = 0.47, 95% CI = 0.28–0.80, P = 0.006), lymph node metastases (OR = 0.55, 95% CI = 0.36–0.84, P = 0.005) and ER status (OR = 1.34, 95% CI = 1.03–1.73, P = 0.003) in breast cancer. Furthermore, the sensitivity and specificity for all included studies were 0.444 (95% CI: 0.321–0.575, P < 0.0001) and 0.976 (95% CI: 0.916–0.993, P < 0.0001), respectively. These results suggested that APC promoter methylation was associated with breast cancer risk, and it could be a valuable biomarker for diagnosis, treatment and prognosis of breast cancer.

APC gene promoter aberrant methylation in serum as a biomarker for breast cancer diagnosis: A meta-analysis

Background

The aim of this study was to evaluate the clinical efficacy of APC gene promoter methylation in serum as a biomarker for breast cancer (BC) diagnosis.

Methods

Two reviewers systematically searched online resources to identify the publications relevant to APC gene promoter methylation and BC. The data of true positive, false positive, false negative, and true negative were extracted from each included study and pooled for diagnostic sensitivity, specificity, and summary receiver operating characteristic curve.

Results

Twelve studies finally fulfilled the inclusion criteria and were included in this meta‐analysis. The diagnostic sensitivity, specificity, positive and negative likelihood ratio, diagnostic odds ratio, and area under the receiver operating characteristic curve were 0.20 (95% confidence interval [CI] 0.17–0.23), 0.96 (95% CI 0.93–0.97), 3.69 (95% CI 1.60–8.50), 0.83 (95% CI 0.75–0.92), 4.58 (95% CI 1.85–11.37) and 0.80, respectively. A Deeks’ funnel plot and Egger's line regression test (t = 1.43, P = 0.18) indicated no publication bias was present.

Conclusion

Because of low sensitivity, APC gene promoter methylation in serum was not suitable for BC screening. However, as specificity was very high, detection of serum APC gene promoter methylation could be used as tool to confirm BC.

CYP1A1 and GSTP1 gene variations in breast cancer: a systematic review and case-control study

In first part of this study, a systematic review was designed to explore the involvement of CYP1A1 and GSTP1 genes in breast cancerogenesis. Based on systematic review, we designed a study to screen CYP1A1 and GSTP1 genes for mutation and their possible association with breast carcinogenesis. A total of 400 individuals were collected and analyzed by PCR-SSCP. After sequence analysis of coding region of CYP1A1 we identified eleven mutations in different exons of respective gene. Among these eleven mutations, ~3 folds increased breast cancer risk was found associated with Asp82Glu mutation (OR 2.99; 95% CI 1.26-7.09), with Ser83Thr mutation (OR 2.99; 95% CI 1.26-7.09) and with Glu86Ala mutation (OR 3.18; 95% CI 1.27-7.93) in cancer patients compared to controls. Furthermore, ~4 folds increase in breast cancer risk was found associated with Asp347Glu, Phe398Tyr and 5178delT mutations (OR 3.92; 95% CI 1.35-11.3) in patients compared to controls. The sequence analysis of GSTP1 resulted in identification of total five mutations. Among these five mutations, ~3 folds increase in breast cancer risk was observed associated with 1860G>A mutation, with 1861-1876delCAGCCCTCTGGAGTGG mutation (OR 2.70; 95% CI 1.10-6.62) and with 1861C>A mutation (OR 2.97; 95% CI 1.01-8.45) in cancer patients compared to controls. Furthermore, ~5 folds increase in breast cancer risk was associated with 1883G>T mutation (OR 4.75; 95% CI 1.46-15.3) and ~6 folds increase in breast cancer risk was found associated with Iso105Val mutation (OR 6.43; 95% CI 1.41-29.3) in cancer patients compared to controls. Our finding, based on systematic review and experimental data suggest that the polymorphic CYP1A1 and GSTP1 genes may contribute to risk of developing breast cancer.

Association between aberrant APC promoter methylation and breast cancer pathogenesis: a meta-analysis of 35 observational studies

Background. Adenomatous polyposis coli (APC) is widely known as an antagonist of the Wnt signaling pathway via the inactivation of β-catenin. An increasing number of studies have reported that APC methylation contributes to the predisposition to breast cancer (BC). However, recent studies have yielded conflicting results.

Methods. Herein, we systematically carried out a meta-analysis to assess the correlation between APC methylation and BC risk. Based on searches of the Cochrane Library, PubMed, Web of Science and Embase databases, the odds ratio (OR) with 95% confidence interval (CI) values were pooled and summarized.

Results. A total of 31 articles involving 35 observational studies with 2,483 cases and 1,218 controls met the inclusion criteria. The results demonstrated that the frequency of APC methylation was significantly higher in BC cases than controls under a random effect model (OR = 8.92, 95% CI [5.12–15.52]). Subgroup analysis further confirmed the reliable results, regardless of the sample types detected, methylation detection methods applied and different regions included. Interestingly, our results also showed that the frequency of APC methylation was significantly lower in early-stage BC patients than late-stage ones (OR = 0.62, 95% CI [0.42–0.93]).

Conclusion. APC methylation might play an indispensable role in the pathogenesis of BC and could be regarded as a potential biomarker for the diagnosis of BC.

Correlation of Methylated Circulating Tumor DNA With Response to Neoadjuvant Chemotherapy in Breast Cancer Patients

BACKGROUND

Circulating tumor DNA (ctDNA) is known to harbor tumor-specific genetic or epigenetic alterations. In the present study, the correlation of ctDNA with tumor response to neoadjuvant chemotherapy (NAC) was evaluated in primary breast cancer patients.

PATIENTS AND METHODS

Plasma samples were obtained from 87 primary breast cancer patients (stage II-III) before and after NAC, as well as 1 year after surgery. Methylated ctDNA (met-ctDNA) was determined by one-step methylation-specific PCR (OS-MSP) for the promoter region of RASSF1A.

RESULTS

The positivity (23.0%, 20/87) of met-ctDNA before NAC was significantly (P < .05) higher than that of carcinoembryonic antigen (CEA) (8.6%) and cancer-associated antigen (CA) 15-3 (7.4%). In the patients with positive met-ctDNA before NAC, met-ctDNA significantly decreased after NAC in those with disease that responded to therapy (P = .006), but not in patients whose disease did not respond to therapy. Met-ctDNA after NAC was found to be significantly (P = .008) correlated to the extent of residual tumor burden. Of the 7 patients who showed an increase in met-ctDNA at 1 year after surgery, 3 developed recurrence.

CONCLUSION

Met-ctDNA is a more sensitive marker than CEA and CA15-3, and it might be useful in monitoring the clinical tumor response to NAC. In addition, the potential use of met-ctDNA as a tumor marker for monitoring postoperative recurrence has been suggested.

Detection and monitoring of hypermethylated RASSF1A in serum from patients with metastatic breast cancer

BACKGROUND

Circulating hypermethylated RASSF1A could be a novel and potential useful marker for monitoring patients with metastatic breast cancer. Technical obstacles include fragmentation of the circulating DNA, fluctuations in the concentration, low concentrations of circulating tumor DNA, and different locations of methylation in the RASSF1A gene among patients. One common method for detection of hypermethylated genes is sodium bisulfite conversion of non-methylated cytosine to uracil, followed by detection with PCR. However, the method relies on full conversion of all non-methylated cytosines, cause strand breaks, and loss of DNA. Alternatively, methylation-sensitive restriction enzymes have been used to digest genomic DNA, as well as sodium bisulfite-treated DNA. By flanking different regions of the RASSF1A with different PCR primer pairs, we analyzed for methylated genomic regions resistant to cleavage by the methylation-sensitive restriction enzymes HpaII and BstUI. The goal was to find region(s) in RASSF1A with high sensitivity and specificity that could be used for monitoring.

RESULTS

The serum was spiked with non-human control DNA. By tracing the spiking control, the isolation procedure of the rare circulating tumor DNA was initially optimized. By analysis of production of PCR amplicons from HpaII- or BstUI-treated DNA isolated from 24 patients with metastatic breast cancer, we located four regions resulting in sensitivities from 63 to 83 %. When examining samples from 24 control subjects, these four regions gave a specificity of 100 %. Among these four regions, the primer pair with the highest PCR efficacy was selected to monitor the RASSF1A concentration in 31 collected serum samples. The spiked DNA was then used to calculate the tumor RASSF1A concentrations independent of fluctuations in circulating non-tumor DNA. As a proof of principle, there was concordance in the kinetics of the RASSF1A and the serological cancer biomarkers CA 15-3, CEA, and TPA.

CONCLUSIONS

Methylation-sensitive restriction enzymes may be a useful methodological approach for monitoring circulating hypermethylated RASSF1A among patients with metastatic breast cancer.

Tumor-Related Methylated Cell-Free DNA and Circulating Tumor Cells in Melanoma

Solid tumor release into the circulation cell-free DNA (cfDNA) and circulating tumor cells (CTCs) which represent promising biomarkers for cancer diagnosis. Circulating tumor DNA may be studied in plasma from cancer patients by detecting tumor specific alterations, such as genetic or epigenetic modifications. Ras association domain family 1 isoform A (RASSF1A) is a tumor suppressor gene silenced by promoter hypermethylation in a variety of human cancers including melanoma. The aim of the present study was to assess the diagnostic performance of a tumor-related methylated cfDNA marker in melanoma patients and to compare this parameter with the presence of CTCs. RASSF1A promoter methylation was quantified in cfDNA by qPCR in a consecutive series of 84 melanoma patients and 68 healthy controls. In a subset of 68 cases, the presence of CTCs was assessed by a filtration method (Isolation by Size of Epithelial Tumor Cells, ISET) as well as by an indirect method based on the detection of tyrosinase mRNA by RT-qPCR. The distribution of RASSF1A methylated cfDNA was investigated in cases and controls and the predictive capability of this parameter was assessed by means of the area under the ROC curve (AUC). The percentage of cases with methylated RASSF1A promoter in cfDNA was significantly higher in each class of melanoma patients (in situ, invasive and metastatic) than in healthy subjects (Pearson chi-squared test, p < 0.001). The concentration of RASSF1A methylated cfDNA in the subjects with a detectable quantity of methylated alleles was significantly higher in melanoma patients than in controls. The biomarker showed a good predictive capability (in terms of AUC) in discriminating between melanoma patients and healthy controls. This epigenetic marker associated to cfDNA did not show a significant correlation with the presence of CTCs, but, when the two parameters are jointly considered, we obtain a higher sensitivity of the detection of positive cases in invasive and metastatic melanomas. Our data suggest that cell-free tumor DNA and CTCs represent two complementary aspects of the liquid biopsy which may improve the diagnosis and the clinical management of melanoma patients.

Role of Circulating Cell-Free DNA in Cancers

Liquid biopsy is a term used to describe non-invasive tests, which provide information about disease conditions through analysis of circulating cell-free DNA and circulating tumor cells from peripheral blood samples. In patients with cancer, the concentration of cell-free DNA increases, and structural, sequence, and epigenetic changes to DNA can be observed through the disease process and during therapy. Furthermore, cell-free DNA released by the tumor contains the same variants as those in the tumor cells. Therefore, cell-free DNA allows non-invasive assessment of cancer in real time. This review summarizes the origin of cell-free DNA, recent advancements in the detection of cell-free DNA, a possible role in metastasis, and its importance as a non-invasive diagnostic assay for cancer.

Aberrant GSTP1 promoter methylation is associated with increased risk and advanced stage of breast cancer: a meta-analysis of 19 case-control studies

BACKGROUND

Glutathione S-transferase P1 (GSTP1) has been reported to function as a tumor suppressor gene in various types of human cancers. Aberrant methylation of tumor-related genes at the promoter regions can inactivate genes, which is important in the carcinogenesis of breast cancer. However, the role of GSTP1 promoter methylation in the occurrence of breast cancer and its relationship with tumor stage and histological grade has not been fully elucidated. Thus, we carried out a meta-analysis to yield a more accurate association.

METHODS

A systematically literature search was made on PubMed, EMBASE and Web of Science databases for eligible studies. The odds ratio (OR) and 95 % confidence interval (95 % CI) were calculated by RevMan 5.2 software. Subgroup and sensitivity analyses were conducted to explore the source of heterogeneity.

RESULTS

Eventually, 17 articles involving 19 case-control studies were included in the present meta-analysis. Overall, the pooled results indicated that aberrant GSTP1 promoter methylation was significantly associated with the risk of breast cancer (OR = 7.85, 95 % CI = 5.12-12.01; Caucasians OR = 7.23, 95 % CI = 3.76-13.90 and Asians OR = 11.71, 95 % CI = 5.69-24.07). Furthermore, our results revealed that GSTP1 promoter methylation was more often observed in late-stage breast cancer patients compared with early-stage ones (OR = 1.84, 95 % CI = 1.32-2.58). However, no significant association was identified between GSTP1 promoter methylation and histological grade (OR = 0.74, 95 % CI = 0.43-1.26).

CONCLUSIONS

The results indicated that GSTP1 promoter methylation probably plays an important role in breast carcinogenesis, which could serve as an effective biomarker for the diagnosis and monitor of breast cancer.

Methylated APC and RASSF1A in multiple specimens contribute to the differential diagnosis of patients with undetermined solitary pulmonary nodules

BACKGROUND

Inactivation of tumor-suppressor gene (TSG) by promoter hypermethylation has been reported in many tumor types, including lung cancer. This study was designed to determine the methylated APC and RASSF1A genes in tumor tissue, serum and plasma of patients with early stage lung cancer.

METHODS

Eighty-nine patients with undetermined solitary pulmonary nodules detected upon CT-scan were recruited in this study. DNA samples were extracted from biopsy tissues, serum and plasma and QMSP of APC and RASSF1A was carried out after bisulfite conversion. The 89 patients consist of 58 stage I lung cancer patients and 31 benign lung disease according to pathological report. Twenty-six cancer patients had matched biopsy tumor tissue, serum and plasma samples.

RESULTS

The methylation rates of APC and RASSF1A were 59.0% and 66.1% in biopsy tissues, 42.5% and 52.5% in serum, and 24.1% and 43.1% in plasma of cancer patients. For RASSF1A, different samples all showed a significant difference between cancer group and benign group (P<0.05). However, APC gene only explored the P value less than 0.05 in plasma result. Towards the 26 lung cancer patients with three matched samples, methylation rate in each sample type was more than 50.0% and displayed no difference.

CONCLUSIONS

Evaluation of APC and RASSF1A promoter methylation by using QMSP appears to be very useful for the differential diagnosis of patients with undetermined solitary pulmonary nodules. Our results also suggested that plasma might be the best sample for clinical detection of early stage lung.

Integrated analysis of DNA methylation, immunohistochemistry and mRNA expression, data identifies a methylation expression index (MEI) robustly associated with survival of ER-positive breast cancer patients

Identification of prognostic gene expression signatures may enable improved decisions about management of breast cancer. To identify a prognostic signature for breast cancer, we performed DNA methylation profiling and identified methylation markers that were associated with expression of ER, PR, HER2, CK5/6, and EGFR proteins. Methylation markers that were correlated with corresponding mRNA expression levels were identified using 208 invasive tumors from a population-based case-control study conducted in Poland. Using this approach, we defined the methylation expression index (MEI) signature that was based on a weighted sum of mRNA levels of 57 genes. Classification of cases as low or high MEI scores was related to survival using Cox regression models. In the Polish study, women with ER-positive low MEI cancers had reduced survival at a median of 5.20 years of follow-up, HR = 2.85 95 % CI = 1.25-6.47. Low MEI was also related to decreased survival in four independent datasets totaling over 2500 ER-positive breast cancers. These results suggest that integrated analysis of tumor expression markers, DNA methylation, and mRNA data may be an important approach for identifying breast cancer prognostic signatures. Prospective assessment of MEI along with other prognostic signatures should be evaluated in future studies.

Sox17 promoter methylation in plasma DNA is associated with poor survival and can be used as a prognostic factor in breast cancer

Aberrant DNA methylation that leads to the inactivation of tumor suppressor genes is known to play an important role in the development and progression of breast cancer. Methylation status of cancer-related genes is considered to be a promising biomarker for the early diagnosis and prognosis of tumors. This study investigated the methylation status of the Sox17 gene in breast cancer tissue and its corresponding plasma DNA to evaluate the association of methylation levels with clinicopathological parameters and prognosis.The methylation status of the Sox17 gene promoter was evaluated with methylation-specific polymerase chain reaction (MSP) in 155 paired breast cancer tissue and plasma samples and in 60 paired normal breast tissue and plasma samples. Association of Sox17 methylation status with clinicopathological parameters was analyzed by χ tests. Overall and disease-free survival (DFS) curves were calculated using Kaplan-Meier analysis, and the differences between curves were analyzed by log-rank tests.The frequency of Sox17 gene methylation was 72.9% (113/155) in breast cancer tissues and 58.1% (90/155) in plasma DNA. Sox17 gene methylation was not found in normal breast tissues or in their paired plasma DNA. There was a significant correlation of Sox17 methylation between corresponding tumor tissues and paired plasma DNA (r = 0.688, P < 0.001). Aberrant Sox17 methylation in cancer tissues and in plasma DNA was significantly associated with the tumor node metastasis stage (P = 0.035 and P = 0.001, respectively) and with lymph node metastasis (P < 0.001 and P = 0.001, respectively). Kaplan-Meier survival curves showed that aberrant Sox17 promoter methylation in cancer tissues and plasma DNA was associated with poor DFS (P < 0.005) and overall survival (OS) (P < 0.005). Multivariate analysis showed that Sox17 methylation in plasma DNA was an independent prognostic factor in breast cancer for both DFS (P = 0.020; hazard ratio [HR] = 2.142; 95% confidence interval [CI]: 1.128-4.067) and for OS (P = 0.001; HR = 4.737; 95% CI: 2.088-10.747).Sox17 gene promoter methylation may play an important role in breast cancer progression and could be used as a prognostic biomarker to identify patients at risk of developing metastasis or recurrence after mastectomy.

Methylated DNA and high total DNA levels in the serum of patients with breast cancer following neoadjuvant chemotherapy are predictive of a poor prognosis

In a previous study, we established a one-step methylation-specific polymerase chain reaction (OS-MSP) assay for the detection of methylated DNA (met-DNA) and total DNA levels in serum. For the present study, this OS-MSP assay was used for patients with breast cancer treated with neoadjuvant chemotherapy (NAC) in order to investigate the prognostic significance of met-DNA and total DNA levels. Following treatment with NAC and prior to surgery, serum samples obtained from 120 patients with stage II/III breast cancer were subjected to the OS-MSP assay for analysis of the glutathione S-transferase pi 1, Ras association (RalGDS/AF-6) domain family member 1 and retinoic acid receptor β2 genes. The detection of methylation in a minimum of one of these genes indicated a positive outcome of the assay. The total DNA content of the serum was also determined. Of the 120 stage II/III patients, seven (6%) were positive for met-DNA in serum and showed a significantly worse overall survival (OS) time compared with patients negative for met-DNA (n=113) (5-year OS, 43 vs. 85%; P=0.002). The patients with high total DNA levels in serum (n=40) also showed a significantly worse OS compared with those with low total DNA levels (n=80) (65 vs. 91%; P<0.001). The presence of met-DNA and high total DNA levels in the serum were found to be significant prognostic factors that are independent of a pathological complete response by multivariate analysis. Following NAC, met-DNA and high total DNA levels in the serum detected with the OS-MSP assay constitute novel prognostic factors for patients with breast cancer; this may be clinically useful for the prognosis prediction for patients who do not achieve a pathological complete response following NAC.

Methylated DNA for monitoring tumor growth and regression: how do we get there?

A wide range of protein cancer biomarkers is currently recommended in international guidelines for monitoring the growth and regression of solid tumors. However, a number of these markers are also present in low concentrations in blood obtained from healthy individuals and from patients with benign diseases. In contrast, evidence has accumulated that suggests that modified methylated DNA is strongly related to the cancer phenotype. The modifications found in modified methylated DNA include a global loss of methylation in the genomes of the tumor cells as well as focal hypermethylation of gene promoters. Because tumor cells naturally secrete DNA and upon cell death leak DNA, modified methylated DNA can be detected in blood, urine, sputum and other body fluids. At present international guidelines do not include recommendations for monitoring modified methylated DNA. The low level of evidence can partly be explained by incomplete collection of serial blood samples, by analytical challenges, and by lack of knowledge of how monitoring studies should be designed and how serial marker data obtained from individual patients should be interpreted. Here, we review the clinical validity and utility of methylated DNA for monitoring the activity of malignant disease.

Real-time liquid biopsy in cancer patients: fact or fiction?

Distant metastases harbor unique genomic characteristics not detectable in the corresponding primary tumor of the same patient and metastases located at different sites show a considerable intrapatient heterogeneity. Thus, the mere analysis of the resected primary tumor alone (current standard practice in oncology) or, if possible, even reevaluation of tumor characteristics based on the biopsy of the most accessible metastasis may not reveal sufficient information for treatment decisions. Here, we propose that this dilemma can be solved by a new diagnostic concept: liquid biopsy, that is, analysis of therapeutic targets and drug resistance-conferring gene mutations on circulating tumor cells (CTC) and cell-free circulating tumor DNA (ctDNA) released into the peripheral blood from metastatic deposits. We discuss the current challenges and future perspectives of CTCs and ctDNA as biomarkers in clinical oncology. Both CTCs and ctDNA are interesting complementary technologies that can be used in parallel in future trials assessing new drugs or drug combinations. We postulate that the liquid biopsy concept will contribute to a better understanding and clinical management of drug resistance in patients with cancer.

Hide and seek: tell-tale signs of breast cancer lurking in the blood

Breast cancer treatment is improving due to the introduction of new drugs, guided by molecular testing of the primary tumour for mutations/oncogenic drivers (e.g. HER2 gene amplification). However, tumour tissue is not always available for molecular analysis, intra-tumoural heterogeneity is common and the "cancer genome" is known to evolve with time, particularly following treatment as resistance develops. After resection, those patients with only residual micrometastases are likely to be cured but those with radiologically detectable overt disease are not. Thus, the discovery of blood test(s) that could (1) alert clinicians to early primary or recurrent disease and (2) monitor response to treatment could impact significantly on mortality. Towards this, we and others have focused on molecular profiling of circulating nucleic acids isolated from plasma, both cell-free DNA (cfDNA) and microRNAs, and the relationship of these to circulating tumour cells (CTCs). This review considers the utility of each as circulating biomarkers in breast cancer with particular emphasis on the bioinformatic tools available to support molecular profiling.

Circulating nucleic acids as biomarkers in breast cancer

During tumor development, tumor cells release their nucleic acids into the blood circulation. This process occurs by apoptotic and necrotic cell deaths along with active cell secretion, resulting in high levels of circulating DNA, mRNA, and microRNA in the blood of patients with breast cancer. As circulating cell-free tumor nucleic acids may reflect the characteristics of the primary tumor and even of micrometastatic cells, they may be excellent blood biomarkers for screening breast cancer. Assays that allow the repetitive monitoring of patients by using blood samples as liquid biopsy may be efficient in assessing cancer progression in patients whose tumor tissue is not available. This review evaluates the recent data on the potential use of circulating cell-free nucleic acids as biomarkers for breast cancer.

Strategies for discovery and validation of methylated and hydroxymethylated DNA biomarkers

DNA methylation, consisting of the addition of a methyl group at the fifth-position of cytosine in a CpG dinucleotide, is one of the most well-studied epigenetic mechanisms in mammals with important functions in normal and disease biology. Disease-specific aberrant DNA methylation is a well-recognized hallmark of many complex diseases. Accordingly, various studies have focused on characterizing unique DNA methylation marks associated with distinct stages of disease development as they may serve as useful biomarkers for diagnosis, prognosis, prediction of response to therapy, or disease monitoring. Recently, novel CpG dinucleotide modifications with potential regulatory roles such as 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine have been described. These potential epigenetic marks cannot be distinguished from 5-methylcytosine by many current strategies and may potentially compromise assessment and interpretation of methylation data. A large number of strategies have been described for the discovery and validation of DNA methylation-based biomarkers, each with its own advantages and limitations. These strategies can be classified into three main categories: restriction enzyme digestion, affinity-based analysis, and bisulfite modification. In general, candidate biomarkers are discovered using large-scale, genome-wide, methylation sequencing, and/or microarray-based profiling strategies. Following discovery, biomarker performance is validated in large independent cohorts using highly targeted locus-specific assays. There are still many challenges to the effective implementation of DNA methylation-based biomarkers. Emerging innovative methylation and hydroxymethylation detection strategies are focused on addressing these gaps in the field of epigenetics. The development of DNA methylation- and hydroxymethylation-based biomarkers is an exciting and rapidly evolving area of research that holds promise for potential applications in diverse clinical settings.

GSTP1 methylation and polymorphism increase the risk of breast cancer and the effects of diet and lifestyle in breast cancer patients

Glutathione S-transferases (GSTs) are an important group of isoenzymes that play an essential role in the detoxification of carcinogens. Polymorphism at exon 5 of the GST π family decreases the catalytic activity and affects the detoxification ability of the enzyme, GSTP1. GSTP1 promoter hypermethylation and loss of expression are frequently observed in various types of carcinoma. We hypothesized that somatic epigenetic modification in homozygous mutants increases the degree to which breast cancer risk is affected by lifestyle factors and dietary habits. The present study used tumor biopsies and blood samples from 215 breast cancer patients and 215 blood samples from healthy donors. GSTP1 polymorphism was studied using PCR-restriction fragment length polymorphism, methylation using methylation-specific PCR and loss of expression using immunohistochemistry and western blotting. No significant increase was observed in the breast cancer risk of individuals with the mutant (Val) allele [odds ratio (OR), 1.48; 95% confidence interval (CI), 0.97–2.26 for heterozygotes; OR, 1.42; 95% CI, 0.86–2.42 homozygous mutants]. GSTP1 promoter hypermethylation was detected in one-third of tumor biopsies (74/215) and was found to be associated with a loss of expression. Genotype and tumor methylation associations were not observed. Estrogen (ER) and progesterone (PR) receptor-positive tumors had a higher methylation frequency. GSTP1 polymorphism was not associated with increased promoter hypermethylation. The results suggest that GSTP1 methylation is a major event in breast carcinogenesis and may act as a tumor-specific biomarker.

Methylated DNA and total DNA in serum detected by one-step methylation-specific PCR is predictive of poor prognosis for breast cancer patients

PURPOSE

We recently developed the one-step methylation-specific PCR (OS-MSP) assay which can detect methylated DNA (met-DNA) in serum with high sensitivity. To examine its prognostic value, we applied this new assay to the detection of met-DNA in serum of breast cancer patients.

METHODS

Serum samples taken before surgery from 336 primary invasive breast cancer patients were subjected to the OS-MSP assay for the promoter regions of GSTP1, RASSF1A, and RARβ2. The assay outcome was considered positive when methylation was detected in at least one of these three genes. Total DNA content in serum was also determined.

RESULTS

Of the 336 stage I/II patients, 33 (10%) were positive for met-DNA in serum and showed a significantly worse overall survival (OS) rate at 100 months (78 vs. 95%; p = 0.002) than those with negative findings (n = 303). Patients with high total DNA in serum (n = 112) also showed a significantly worse OS rate at 100 months (86 vs. 97%; p = 0.001) than those with low total DNA in serum (n = 224). Moreover, patients both positive for met-DNA and with high total DNA in serum (n = 18) showed a much worse OS rate at 100 months (65 vs. 94%; p < 0.001) than the others (n = 318).

CONCLUSIONS

Met-DNA in serum detected with the OS-MSP assay constitutes a significant and independent prognostic factor, and its combination with total DNA in serum seems to be even more effective for prediction of prognosis for breast cancer patients.

DNA methylation-based biomarkers in serum of patients with breast cancer

Alterations of genetic and epigenetic features can provide important insights into the natural history of breast cancer. Although DNA methylation analysis is a rapidly developing field, a reproducible epigenetic blood-based assay for diagnosis and follow-up of breast cancer has yet to be successfully developed into a routine clinical test. The aim of this study was to review multiple serum DNA methylation assays and to highlight the value of those novel biomarkers in diagnosis, prognosis and prediction of therapeutic outcome. Serum is readily accessible for molecular diagnosis in all individuals from a peripheral blood sample. The list of hypermethylated genes in breast cancer is heterogeneous and no single gene is methylated in all breast cancer types. There is increasing evidence that a panel of epigenetic markers is essential to achieve a higher sensitivity and specificity in breast cancer detection. However, the reported percentages of methylation are highly variable, which can be partly explained by the different sensitivities and the different intra-/inter-assay coefficients of variability of the analysis methods. Moreover, there is a striking lack of receiver operating characteristic (ROC) curves of the proposed biomarkers. Another point of criticism is the fact that 'normal' patterns of DNA methylation of some tumor suppressor and other cancer-related genes are influenced by several factors and are often poorly characterized. A relatively frequent methylation of those genes has been observed in high-risk asymptomatic women. Finally, there is a call for larger prospective cohort studies to determine methylation patterns during treatment and follow-up. Identification of patterns specific for a differential response to therapeutic interventions should be useful. Only in this way, it will be possible to evaluate the predictive and prognostic characteristics of those novel promising biomarkers.

Aberrant methylation of the PTPRO gene in peripheral blood as a potential biomarker in esophageal squamous cell carcinoma patients

Epigenetic inactivation of protein tyrosine phosphatase receptor-type O (PTPRO), a new member of the PTP family, has been described in several forms of cancer. We evaluated PTPRO promoter hypermethylation as a potential biomarker in esophageal squamous cell carcinoma (ESCC). This alteration was observed in 27 (75%) of 36 primary tumors and correlated significantly with depth of invasion (T-stage, P = 0.013). Among matched peripheral blood samples from ESCC patients, 13 (36.1%) of 36 exhibited detectable methylated PTPRO in plasma, while 15 (41.7%) of 36 had this abnormality in buffy coat. No methylated PTPRO was observed in normal peripheral blood samples from 10 healthy individuals. In addition, demethylation by 5-aza-dC treatment led to gene reactivation in PTPRO-methylated and -silenced ESCC cell lines. To our knowledge, this is the first report of methylated PTPRO as a noninvasive tumor biomarker in peripheral blood. These findings suggest that hypermethylated PTPRO occurs frequently in ESCC. Further, detection in peripheral blood of ESCC patients suggests potential clinical application for noninvasive diagnosis and disease monitoring.

Circulating tumor cells and circulating tumor DNA

Solid tumors derived from epithelial tissues (carcinomas) are responsible for 90% of all new cancers in Europe, and the main four tumor entities are breast, prostate, lung, and colon cancer. Present tumor staging is mainly based on local tumor extension, metastatic lymph node involvement, and evidence of overt distant metastasis obtained by imaging technologies. However, these staging procedures are not sensitive enough to detect early tumor cell dissemination as a key event in tumor progression. Many teams have therefore focused on the development of sensitive assays that allow the specific detection of single tumor cells or small amounts of cell-free tumor DNA in the peripheral blood of cancer patients. These methods allow the detection and characterization of early metastatic spread and will provide unique insights into the biology of metastatic progression of human tumors, including the effects of therapeutic interventions.

Cell-free nucleic acids as biomarkers in cancer patients

DNA, mRNA and microRNA are released and circulate in the blood of cancer patients. Changes in the levels of circulating nucleic acids have been associated with tumour burden and malignant progression. In the past decade a wealth of information indicating the potential use of circulating nucleic acids for cancer screening, prognosis and monitoring of the efficacy of anticancer therapies has emerged. In this Review, we discuss these findings with a specific focus on the clinical utility of cell-free nucleic acids as blood biomarkers.