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Altered DNA methylation is ubiquitous in human cancers and specific methylation changes are often correlated with clinical features. DNA methylation biomarkers, which use those specific methylation changes, provide a range of opportunities for early detection, diagnosis, prognosis, therapeutic stratification and post-therapeutic monitoring. Here we review current approaches to developing and applying DNA methylation biomarkers in cancer therapy. We discuss the obstacles that have so far limited the routine use of DNA methylation biomarkers in clinical settings and describe ways in which these obstacles can be overcome. Finally, we summarize the current state of clinical implementation for some of the most widely studied and well-validated DNA methylation biomarkers, including SEPT9, VIM, SHOX2, PITX2 and MGMT.

Background Constitutional BRCA1 epimutations (promoter hypermethylation) are associated with an elevated risk of triple-negative breast cancer and high-grade serous ovarian cancer. While MGMT epimutations are frequent in colon cancer, glioblastoma, and B-cell lymphoma, it remains unknown whether constitutional MGMT epimutations are associated with risk of any of these malignancies. Methods We designed a nested case–control study, assessing potential associations between MGMT epimutations in blood from healthy individuals and subsequent risk of incident cancer. The study cohort was drawn from postmenopausal women, participating in the Women’s Health Initiative (WHI) study, who had not been diagnosed with either colon cancer, glioblastoma, or B-cell lymphoma prior to study entry. The protocol included n  = 400 women developing incident left-sided and n  = 400 women developing right-sided colon cancer, n  = 400 women developing diffuse large B-cell lymphomas, all matched on a 1:2 basis with cancer-free controls, and n  = 195 women developing incident glioblastoma multiforme, matched on a 1:4 basis. All cancers were confirmed in centralized medical record review. Blood samples, collected at entry, were analyzed for MGMT epimutations by massive parallel sequencing. Associations between MGMT methylation and incident cancers were analyzed by Cox proportional hazards regression. Results Analyzing epimutations affecting the key regulatory area of the MGMT promoter, the hazard ratio (HR) was 1.07 (95% CI 0.79–1.45) and 0.80 (0.59–1.08) for right- and left-sided colon cancer, respectively, 1.13 (0.78–1.64) for glioblastoma, and 1.11 (0.83–1.48) for diffuse large B-cell lymphomas. Sensitivity analyses limited to subregions of the MGMT promoter and to individuals with different genotypes of a functional SNP in the MGMT promoter (rs16906252), revealed no significant effect on HR for any of the cancer forms. Neither did we observe any effect of rs16906252 status on HR for any of the cancer forms among individuals methylated or non-methylated at the MGMT promoter. Conclusions Constitutional MGMT promoter methylation in normal tissue is not associated with an increased risk of developing colon cancer, glioblastoma, or B-cell lymphoma.

Constitutional epimutation of the two major mismatch repair genes, MLH1 and MSH2, has been identified as an alternative mechanism that predisposes to the development of Lynch syndrome. In the present work, we aimed to investigate the prevalence of MLH1 constitutional methylation in colorectal cancer (CRC) patients with abnormal expression of the MLH1 protein in their tumors. In a series of 38 patients who met clinical criteria for Lynch syndrome genetic testing, with loss of MLH1 expression in the tumor and with no germline mutations in the MLH1 gene (35/38) or with tumors presenting the BRAF p.Val600Glu mutation (3/38), we screened for constitutional methylation of the MLH1 gene promoter using methylation‐specific multiplex ligation‐dependent probe amplification (MS‐MLPA) in various biological samples. We found four (4/38; 10.5%) patients with constitutional methylation in the MLH1 gene promoter. RNA studies demonstrated decreased MLH1 expression in the cases with constitutional methylation when compared with controls. We could infer the mosaic nature of MLH1 constitutional hypermethylation in tissues originated from different embryonic germ layers, and in one family we could show that it occurred de novo. We conclude that constitutional MLH1 methylation occurs in a significant proportion of patients who have loss of MLH1 protein expression in their tumors and no MLH1 pathogenic germline mutation. Furthermore, we provide evidence that MLH1 constitutional hypermethylation is the molecular mechanism behind about 3% of Lynch syndrome families diagnosed in our institution, especially in patients with early onset or multiple primary tumors without significant family history. This work aimed to investigate the prevalence of MLH1 constitutional methylation in colorectal cancer patients with abnormal expression of the MLH1 protein in their tumors and without germline mutations. We provide evidence that MLH1 constitutional hypermethylation is the molecular mechanism behind about 3% of Lynch syndrome families, most likely in patients with early onset or multiple primary tumors without significant family history.

PurposeConstitutional BRCA1 promoter methylation has been identified as a potential risk factor for breast cancer (BC) in the Caucasian population. However, this data is lacking for BC patients of Asian origin. Therefore, we assessed the contribution of constitutional BRCA1 promoter methylation in Pakistani BC patients.MethodsA total of 385 BRCA1/2-negative index BC patients (197 early-onset BC (≤ 30 years), 152 familial BC, 17 familial BC and ovarian cancer, 19 male BC) and 107 healthy controls were screened for the constitutional BRCA1 promoter methylation by methylation-sensitive high-resolution melting assay. Overall, 131 patients displayed triple-negative BC (TNBC) and 254 non-TNBC phenotypes. The prevalence of BRCA1 promoter methylation was calculated based on clinicopathological characteristics using univariable and multivariable logistic regression models.ResultsConstitutional BRCA1 promoter methylation was identified in 19.5% (75/385) of BC patients and 13.1% (14/107) of controls. The frequency of methylation was higher in early-onset BC (23.4% vs. 13.1%, P = 0.035) and TNBC patients (29.0% vs. 13.1%, P = 0.004) compared to controls. Methylation was also more prevalent in patients with high-grade than low-grade tumors (21.7% vs. 12.2%, P = 0.034) and progesterone receptor (PR)-negative than PR-positive tumors (26.0% vs. 13.9%, P = 0.004). Constitutional BRCA1 promoter methylation remained independently associated with TNBC phenotype (odds ratio 1.99; 95% CI 1.12–3.54; P = 0.02) after adjusting for BC diagnosis age, tumor grade, ER, and PR status.ConclusionConstitutional BRCA1 promoter methylation is associated with TNBC and can serve as a non-invasive blood-based biomarker for Pakistani TNBC patients.

(1) Background: MLH1 hypermethylation is an epigenetic alteration in the tumorigenesis of colorectal cancer (CRC) and endometrial cancer (EC), causing gene silencing, and, as a consequence, microsatellite instability. Commonly, MLH1 hypermethylation is considered a somatic and sporadic event in cancer, and its detection is recognized as a useful tool to distinguish sporadic from inherited conditions (such as, Lynch syndrome (LS)). However, MLH1 hypermethylation has been described in rare cases of CRC and EC in LS patients. (2) Methods: A total of 61 cancers (31 CRCs, 27 ECs, 2 ovarian cancers, and 1 stomach cancer) from 56 patients referred to cancer genetic counselling were selected for loss of MLH1 protein expression and microsatellite instability. All cases were investigated for MLH1 promoter methylation and MLH1/PMS2 germline variants. (3) Results: Somatic MLH1 promoter hypermethylation was identified in 16.7% of CRC and in 40% of EC carriers of MLH1 germline pathogenic variants. In two families, primary and secondary MLH1 epimutations were demonstrated. (4) Conclusions: MLH1 hypermethylation should not be exclusively considered as a sporadic cancer mechanism, as a non-negligible number of LS-related cancers are MLH1 hypermethylated. Current flow charts for universal LS screening, which include MLH1 methylation, should be applied, paying attention to a patient’s family and personal history.

Constitutional epimutations of the MLH1 gene are an alternative cause of Lynch syndrome, in which inactivation of an allele of a mismatch repair (MMR) gene results from MLH1 promoter methylation, rather than a pathogenic genetic variant. These epimutations are often mosaic, and methylation levels ranging from ~50% monoallelic methylation to low‐level methylation (1%–5%) are observed in the blood of MLH1 epimutation carriers. Using a specific and highly sensitive droplet digital methyl‐specific PCR (ddMSP) assay, six patients with very low methylation levels (< 1%) were identified in a series of 142 patients with a MLH1‐methylated tumor diagnosed before age 61, who had been referred to the clinical lab between 2020 and 2024. These patients were initially missed by standard pyrosequencing assay, emphasizing the need for highly sensitive assays for constitutional epimutation screening. To confirm that methylated DNA molecules detected by ddMSP did not correspond to circulating tumor DNA rather than germline DNA, multiple validation analyses were performed, including validation of the constitutional origin of methylation on other sources of germline DNA and tumoral analysis. Taking into account the other patients identified as epimutation carriers by pyrosequencing during the same 5‐year period, 13.1% of patients with a MLH1‐methylated tumor before age 61 were diagnosed as Lynch syndrome patients, which changed their clinical follow‐up. These findings highlight the relevance of recommendations for systematic MLH1 epimutation screening using highly sensitive assays in patients with MLH1‐methylated tumors diagnosed before age 61. Such screening will increase the number of patients diagnosed with Lynch syndrome caused by a MLH1 constitutional epimutation, improving patient care and outcomes, as well as genetic counseling.

Background Normal cell BRCA1 epimutations have been associated with increased risk of triple-negative breast cancer (TNBC). However, the fraction of TNBCs that may have BRCA1 epimutations as their underlying cause is unknown. Neither are the time of occurrence and the potential inheritance patterns of BRCA1 epimutations established. Methods To address these questions, we analyzed BRCA1 methylation status in breast cancer tissue and matched white blood cells (WBC) from 408 patients with 411 primary breast cancers, including 66 TNBCs, applying a highly sensitive sequencing assay, allowing allele-resolved methylation assessment. Furthermore, to assess the time of origin and the characteristics of normal cell BRCA1 methylation, we analyzed umbilical cord blood of 1260 newborn girls and 200 newborn boys. Finally, we assessed BRCA1 methylation status among 575 mothers and 531 fathers of girls with ( n  = 102) and without ( n  = 473) BRCA1 methylation. Results We found concordant tumor and mosaic WBC BRCA1 epimutations in 10 out of 66 patients with TNBC and in four out of six patients with estrogen receptor (ER)-low expression (< 10%) tumors (combined: 14 out of 72; 19.4%; 95% CI 11.1–30.5). In contrast, we found concordant WBC and tumor methylation in only three out of 220 patients with 221 ER ≥ 10% tumors and zero out of 114 patients with 116 HER2-positive tumors. Intraindividually, BRCA1 epimutations affected the same allele in normal and tumor cells. Assessing BRCA1 methylation in umbilical WBCs from girls, we found mosaic, predominantly monoallelic BRCA1 epimutations, with qualitative features similar to those in adults, in 113/1260 (9.0%) of individuals, but no correlation to BRCA1 methylation status either in mothers or fathers. A significantly lower fraction of newborn boys carried BRCA1 methylation (9/200; 4.5%) as compared to girls ( p  = 0.038). Similarly, WBC BRCA1 methylation was found less common among fathers (16/531; 3.0%), as compared to mothers (46/575; 8.0%; p  = 0.0003). Conclusions Our findings suggest prenatal BRCA1 epimutations might be the underlying cause of around 20% of TNBC and low-ER expression breast cancers. Such constitutional mosaic BRCA1 methylation likely arise through gender-related mechanisms in utero, independent of Mendelian inheritance.

Background Lynch syndrome (LS), characterised by an increased risk for cancer, is mainly caused by germline pathogenic variants affecting a mismatch repair gene ( MLH1 , MSH2 , MSH6 , PMS2 ). Occasionally, LS may be caused by constitutional MLH1 epimutation (CME) characterised by soma-wide methylation of one allele of the MLH1 promoter. Most of these are “primary” epimutations, arising de novo without any apparent underlying cis -genetic cause, and are reversible between generations. We aimed to characterise genetic and gene regulatory changes associated with primary CME to elucidate possible underlying molecular mechanisms. Methods Four carriers of a primary CME and three non-methylated relatives carrying the same genetic haplotype were included. Genetic alterations were sought using linked-read WGS in blood DNA. Transcriptome (RNA-seq), chromatin landscape (ATAC-seq, H3K27ac CUT&Tag) and 3D chromatin interactions (UMI-4C) were studied in lymphoblastoid cell lines. The MLH1 promoter SNP (c.-93G > A, rs1800734) was used as a reporter in heterozygotes to assess allele-specific chromatin conformation states. Results MLH1 epimutant alleles presented a closed chromatin conformation and decreased levels of H3K27ac, as compared to the unmethylated allele. Moreover, the epimutant MLH1 promoter exhibited differential 3D chromatin contacts, including lost and gained interactions with distal regulatory elements. Of note, rare genetic alterations potentially affecting transcription factor binding sites were found in the promoter-contacting region of CME carriers. Conclusions Primary CMEs present allele-specific differential interaction patterns with neighbouring genes and regulatory elements. The role of the identified cis -regulatory regions in the molecular mechanism underlying the origin and maintenance of CME requires further investigation.

Background Constitutional primary monoallelic promoter methylation of hereditary cancer genes, although rare, may explain early-onset cancers without family history. Also, promoter methylation of a hereditary cancer gene secondary to a genetic alteration in a methylation regulatory region can cause a hereditary cancer syndrome. This study investigates constitutional promoter methylation as mechanism of inactivation of cancer predisposition genes in genetically unsolved familial and/or early-onset colorectal cancer (CRC) patients. Results Bisulfite-treated peripheral blood DNA from 46 early-onset/familial CRC patients was analyzed using the Illumina Infinium MethylationEPIC BeadChip. One early-onset CRC patient exhibited constitutional, likely monoallelic, methylation of CpG island 102 in LTBP4 , a gene involved in TGF-β signaling. Somatic methylation of this CpG island is common in CRC, and correlates with LTBP4 downregulation. LTBP4 double knockout mice develop colorectal adenomas and carcinomas, supporting the role of this gene in CRC predisposition. No additional cases with constitutional LTBP4 CpG island 102 methylation or enrichment of deleterious LTBP4 variants in CRC patients compared to controls were found. Another early-onset CRC patient exhibited mosaic BRCA1 promoter methylation, typically associated with increased breast and ovarian cancer risk. No somatic second hit in BRCA1 was detected in the patient’s tumor, and homologous recombination deficiency-associated features were inconclusive. Conclusions Our findings suggest that constitutional methylation of LTBP4 CpG island 102 may be associated with increased CRC risk. Identification of additional cases is needed to confirm the existence of a novel CRC predisposition syndrome driven by epigenetic inactivation of LTBP4 , potentially also linked to other clinical phenotypes associated with LTBP4 deficiency, such as pulmonary emphysema. Whether constitutional BRCA1 methylation contributes to CRC risk remains to be determined.

Constitutional epimutations are an alternative to genetic mutations in the etiology of genetic diseases. Some of these epimutations, termed secondary, correspond to the epigenetic effects of cis-acting genetic defects transmitted to the offspring following a Mendelian inheritance pattern. In Lynch syndrome, a few families with such apparently heritable MLH1 epimutations have been reported so far. We designed a long-range polymerase chain reaction next-generation sequencing strategy to screen MLH1 entire gene and applied it to 4 French families with heritable epimutations and 10 additional patients with no proven transmission of their epimutations. This strategy successfully detected the insertion of an Alu element in MLH1 coding sequence in one family. Two previously unreported MLH1 variants were also identified in other epimutation carriers: a nucleotide substitution within intron 1 and a single-nucleotide deletion in the 5′-UTR. Detection of a partial MLH1 duplication in another family required multiplex ligation-dependent probe amplification technology. We demonstrated the segregation of these variants with MLH1 methylation and studied the functional consequences of these defects on transcription. This is the largest cohort of patients with MLH1 secondary epimutations associated with a broad spectrum of genetic defects. This study provides further insight into the complexity of molecular mechanisms leading to secondary epimutations.