Structural and functional disruptions of the epigenome are hallmarks of breast and ovarian carcinogenesis. This review dissects the reciprocal regulatory networks co-operated by DNA methyltransferases (DNMTs), ten-eleven translocation enzymes (TETs), and key non-coding RNAs (microRNAs and lncRNAs). We map the precise molecular mechanisms through which these epigenetic modulators alter chromatin accessibility, drive transcriptional reprogramming, and promote phenotypic plasticity in hormone-dependent malignancies. By systematically contrasting the distinct yet overlapping epigenetic profiles of breast and ovarian tumors, we elucidate how these aberrations dictate clinical outcomes. This comprehensive synthesis offers critical insights into the dual utility of these epigenetic elements as dual-purpose diagnostic biomarkers and druggable therapeutic targets, laying the groundwork for next-generation targeted epigenetical therapies.

Breast cancer is the most commonly diagnosed malignancy in women. Despite advances in diagnostics and treatment, the key molecular mechanisms underlying its development remain incompletely understood. This study aimed to identify novel lncRNA–miRNA–mRNA regulatory networks potentially involved in breast cancer–associated signaling pathways. Using an RT² lncRNA PCR Array and bioinformatic analysis, we identified seven differentially expressed (DE) lncRNAs. Four of these—ADAMTS9-AS2, HAND2-AS1, HOTAIRM1, and MEG3—were prioritized through integrative evaluation. qPCR confirmed their downregulation and aberrant methylation in breast tumor samples. We observed significant positive expression correlations between the pairs ADAMTS9-AS2–MEG3, HAND2-AS1–MEG3, and HOTAIRM1–MEG3, as well as co-methylation among ADAMTS9-AS2–HAND2-AS1, ADAMTS9-AS2–HOTAIRM1, HAND2-AS1–MEG3, and HAND2-AS1–HOTAIRM1, suggesting coordinated regulation. These findings are consistent with data from GEPIA 2.0. Bioinformatic prediction identified TCF7L2 as a common target gene of these lncRNAs, which is involved in the Wnt, Hippo, and MAPK signaling pathways. We also identified several miRNAs interacting with ADAMTS9-AS2. In a cohort of 50 tumor samples, we confirmed inverse associations between ADAMTS9-AS2 expression and levels of miR-106a-5p (rs = –0.46, p = 0.03) and miR-17-5p (rs = –0.41, p = 0.04). Collectively, these findings reveal novel co-regulated lncRNA–miRNA axes and suggest their involvement in key signaling networks in breast cancer, providing a foundation for future functional studies and potential therapeutic targeting.

Background: Ovarian tumors are characterized by asymptomatic progression until their late stages, when at the time of diagnosis the patient already has extensive metastatic disease. In addition to lymphogenous and hematogenous metastasis in ovarian cancer, there are peritoneal dissemination and metastasis to the greater omentum with ascites; moreover, peritoneal carcinomatosis is the predominant route of metastasizing of ovarian cancer. Epigenetic factors, such as gene methylation, regulatory microRNAs and long non-coding RNAs (lncRNAs), contribute to progression of this cancer. Our previous bioinformatic and experimental studies have identified 13 genes of lncRNAs (GAS5, HOTAIR, LINC00472, LINC00886, MAFG-DT, PLUT/PDX1-AS1, SNHG1, SNHG6, SNHG12, SNHG17, TINCR, TP53TG1, TUG1) hypermethylated in the ovarian neoplasms. Aim: To evaluate the clinical significance of methylation levels of 13 lncRNA genes (GAS5, HOTAIR, LINC00472, LINC00886, MAFG-DT, PLUT/PDX1-AS1, SNHG1, SNHG6, SNHG12, SNHG17, TINCR, TP53TG1, TUG1) associated with various types of ovarian cancer metastasis, including lymphogenous, peritoneal, omental, and distant metastases. Methods: The methylation levels of lncRNA genes GAS5, HOTAIR, LINC00472, LINC00886, MAFG-DT, PLUT/PDX1-AS1, SNHG1, SNHG6, SNHG12, SNHG17, TINCR, TP53TG1, TUG1 were analyzed by quantitative real-time methylation-specific polymerase chain reaction. We tested 122 duplicate samples of ovarian neoplasms, including 104 malignancies and 18 borderline tumors, as well as 45 peritoneal macro metastases, collected in the N.N. Blokhin National Medical Research Center of Oncology in 2020 to 2023. The study included 21 samples of primary tumor from patients with lymphogenous metastases, 45 samples from patients with peritoneal dissemination, 61 from those with omental metastases, 49 from patients with ascites, and 9 with distant metastases. Results: The tumor samples from the patients with lymphatic nodes metastases showed a significant increase in the methylation level of two lncRNA genes: SNHG6 (p = 0.044) and SNHG12 (p = 0.006). Peritoneal dissemination was associated with hypermethylation of four lncRNA genes: GAS5, HOTAIR, LINC00472 (p 0.05), and most significantly TINCR (p = 0.001). GAS5, HOTAIR, LINC00886 (p 0.05) and most significantly LINC00472 (p 0.001) hypermethylation was typical for omental metastasis, and that of LINC00472 and LINC00886, with ascites (p 0.05). Peritoneal macroscopic metastases demonstrated increased methylation of MAFG-DT (p 0.001) and TP53TG1 (p 0.001) and desmethylation of LINC00886 (p = 0.003) and SNHG12 (p = 0.002), compared to their primary tumors. Conclusion: We performed the analysis of clinical significance of 13 hypermethylated lncRNA genes in ovarian cancer and were the first to show that 10 genes (GAS5, HOTAIR, LINC00472, LINC00886, MAFG-DT, SNHG6, SNHG12, TINCR, TP53TG1, TUG1) were associated with various types of ovarian tumor metastasis. Also, we were able to determine certain panels of lncRNA, which, if demonstrate abnormal methylation, were specific for lymphogenous and peritoneal metastasis of ovarian tumors.

Objectives. Lung cancer, representing a difficult-to-diagnose heterogeneous malignant neoplasm, is characterized by an asymptomatic course up to late stages, a high incidence of adverse outcomes, and a high probability of metastasis. Its most common form is non-small cell lung cancer (NSCLC). Recent studies have demonstrated a significant role of non-coding RNAs—in particular, microRNAs—in the development of NSCLC. MicroRNAs, which function as post-transcriptional regulators of the expression of protein-coding genes, including those associated with oncogenesis, are involved in the processes of cell proliferation, differentiation, and apoptosis. One of the approaches for regulating the expression of microRNAs themselves is to change the methylation of the CpG island adjacent to the microRNA gene or overlapping it. It has been shown that microRNA genes are several times more likely to undergo methylation than protein-coding genes. The aim of the present work is to study changes in the level of methylation of a number of microRNA genes and compile a potential panel of markers for the diagnosis and prognosis of NSCLC.Methods. Samples of NSCLC tumors were collected and clinically characterized at the Blokhin National Medical Research Center of Oncology, Ministry of Health of the Russian Federation, Moscow, Russia. High-molecular-weight DNA was isolated from tissues using a standard method. The level of methylation was analyzed using bisulfite conversion of DNA and quantitative methyl-specific polymerase chain reaction with real-time detection. The significance of differences between the studied groups was assessed by the nonparametric Mann–Whitney U test for independent samples. Differences were considered significant at p < 0.05.Results. The analysis of methylation levels of microRNA genes revealed a significant (p < 0.05) increase in the methylation level of eight microRNA genes: MIR124-1/2/3, MIR125В-1, MIR129-2, MIR137, MIR375, MIR1258, and MIR339 (p < 0.01, false discovery rate ≤ 0.25). On the basis of receiver operating characteristic analysis, a panel of markers is proposed for the diagnosis of NSCLC according to the nature of methylation of the studied microRNA genes in the tumor and in the normal tissue.Conclusions. Our results, which contribute to the understanding of molecular mechanisms involved in NSCLC development, can be used in the development of new diagnostic and prognostic approaches in clinical oncology.

Metastasis to the lymph nodes is one of the most important factors in the poor prognosis of patients with breast cancer; the five-year survival rate for metastatic breast cancer is less than 30

Ovarian carcinoma (OC) is characterized by asymptomatic development up to the terminal stages and aggressive metastasis. The study of epigenetic regulation by long non-coding RNAs (lncRNA) that control the level of gene expression is supposed to be promising as they also involved in several aberrant mechanisms during oncogenesis to metastases. We aimed to evaluate the antimetastatic potential of MEG3, MAGI2-AS3, SSTR5-AS1, ZEB1-AS1 lncRNAs through the changes in expression and methylation level of OC.

There are three types of metastases in ovarian cancer: lymphogenous, hematogenous, and peritoneal. Dissemination of the tumor in the peritoneum is directly related with the development of ascites and a poor prognosis. The purpose of this study is to determine changes in the methylation level of a group of long non-coding RNA (lncRNA) genes at different stages of ovarian cancer progression. The methylation level of 7 lncRNA genes (LINC00472, LINC00886, MAFG-DT, SNHG1, SNHG6, TP53TG1, and TUG1) was studied by quantitative methyl-specific PCR in 93 samples of ovarian tumors and 75 paired samples of histologically normal tissue, as well as in 29 peritoneal macroscopic metastases. Using the nonparametric Mann—Whitney test, a significant (p<0.001) increase in the level of methylation of the LINC00886, SNHG1, SNHG6, and TUG1 genes in the tumor tissue was shown. For the LINC00472, LINC00886, and SNHG6 genes, a significant relationship was found with the clinical stage (p≤0.001), as well as with the appearance of metastases for the LINC00472 (p<0.001) and SNHG6 (p=0.005) genes. There was a significant increase in the level of methylation of MAFG-DT and TP53TG1 (p<0.001) genes, as well as a decrease in LINC00886 (p=0.003) in peritoneal metastases relative to the primary focus. Methylation of the LINC00472 and SNHG6 genes can be considered as a factor in initiating ovarian cancer metastasis, and methylation of the LINC00886, MAFG-DT, and TP53TG1 genes as a colonization factor for metastases in the peritoneum. Thus, a relationship between methylation of a group of lncRNA genes at different stages of ovarian cancer dissemination was shown, which is important for understanding the mechanisms of these processes and for developing innovative approaches to ovarian cancer therapy.

Xenon stimulates the synthesis of the hormone erythropoietin, which leads to improved oxygen supply to tissues, increased endurance and can be used by athletes to gain an undue advantage in competitions. The World Anti-Doping Agency (WADA) banned its use. The determination of xenon in biological fluids, in particular, in blood plasma samples, is difficult due to the narrow detection window. Its indirect detection is possible by changing in some blood parameters during a clinical analysis (RET%, HGB, HCT, etc.), however, this analysis is nonspecific and the use of other erythropoiesis-stimulating agents can lead to similar changes.Aims: The aim of the study was to search for long-term microRNA markers, the expression of which is specific and markedly altered by inhaled xenon.Methods: Quantitative real-time PCR was performed on CFX96 Bio-Rad analyser using miRCURY® LNA® miRNA SYBR® Green PCR Kit and panels for studying the expression profiles of mature microRNAs of the hypoxia signaling pathway miRCURY LNA™ miRNA Focus Panel.Results: Based on statistical data analysis, it was found that the expression of hsa-miR-378a-3p and hsa-miR-491-5p in blood plasma increases significantly (more than 70 times) when xenon inhalations are used as an erythropoiesis stimulator. Measurement of hematological parameters before and after inhalation showed no significant changes that could affect endurance or give competitive advantages.Conclusion: The evaluated difference in microRNA expression levels before and after administration of the xenon mixture (Xe/O2) makes hsa-miR-378a-3p and hsa-miR-491-5p potential candidates for the role of long-term markers of xenon abuse.

We analyzed changes in the level of methylation of CpG islands in four long non-coding RNA (lncRNA) genes MEG3, ZNF667-AS1, GAS5, and SEMA3B-AS1 as promising markers of breast cancer. Methylation analysis was performed by quantitative methylation-specific PCR on a set of 38 paired (tumor/normal) breast cancer samples. Significantly (p<0.001) increased methylation was shown for three of the four lncRNA genes: MEG3, ZNF667-AS1, and SEMA3B-AS1. We found significant correlations of the methylation level of all the studied lncRNA genes with the stage of cancer and with lymphogenic metastasis, and for MEG3 and ZNF667-AS1 also with the tumor size. Methylation of ZNF667-AS1, and SEMA3B-AS1 genes in breast cancer was detected for the first time. Based on these findings, new potential markers for the diagnosis and prognosis of breast cancer can be proposed.

Ovarian cancer (OC) is the most lethal gynecological cancer worldwide. DNA damage plays an important role in cancer development, and the proteins encoded by XRCC1 and ERCC2 are important components of the DNA repair system. This study aimed to examine the relationship between the rs25487 XRCC1 and rs13181 ERCC2 polymorphisms and the risk of OC development in women from the Moscow region. DNA was isolated from the blood of 129 healthy donors and tissues and blood samples from 125 patients with OC and studied using real-time PCR. An increase in odds ratios (OR) was obtained for OC tissue and blood for both T (OR = 1.46, 95% CI = 1.22 - 1.76, p = 0.00005), and for T/T of rs25487 XRCC1 . The most significant OR values were found for the T/T genotype using the codominant model (OR = 2.11, 95% CI = 1.44 - 3.07, p = 0.00006) and dominant model (OR = 3.13, 95% CI = 1.44 - 6.79, p = 0.0025) for the pooled blood and tissue groups. For rs13181 ERCC2, differences were observed for the T/G genotype in OC tissues (OR = 0.69, 95% CI = 0.51 - 0.92, p = 0.011) in the codominant model. In this study, the association of allele T and genotypes of rs25487 XRCC1 and T/G of rs13181 ERCC2 with OC was shown. Our results indicate that these polymorphisms may be involved in the pathogenesis of OC and are promising for further studies on therapeutic applications in OC.

Genes of the small nucleolar RNA host gene (SNHG) family may participate in oncogenesis through the regulatory functions of encoded long non-coding RNAs (lncRNAs) and by influencing formation of small nucleolar RNAs and ribosome biogenesis. The aim of this work was to evaluate changes in the methylation levels and extent of co-methylation of the SNHG family lncRNA genes (SNHG1, GAS5/SNHG2, SNHG6, SNHG12, SNHG17) in clinical samples of ovarian cancer (OC) as an indication for the similarity of their roles in oncogenesis. Analysis of a representative set of 122 OC samples by quantitative methylation-specific PCR showed a statistically significant (p < 0.01-0.0001) increase in the methylation level of all five studied lncRNA genes. There was also a correlation between the increased methylation levels of GAS5, SNHG6, and SNHG12 and OC progression (clinical stage, tumor size, and metastasis), indicating possible functional significance of hypermethylation of these genes. For four genes (SNHG1, GAS5, SNHG6, and SNHG12), a statistically significant pairwise positive correlation of methylation levels (co-methylation) was observed (rs > 0.35; p ≤ 0.001), which was in agreement with the GEPIA 2.0 data (426 OC samples) showing co-expression of these genes (rs > 0.5; p < 0.001). The correlation between the expression levels of GAS5 and SNHG6 was confirmed by RT-qPCR (rs = 0.46; p = 0.007). Bioinformatics analysis predicted miRNAs common for the SNHG1, GAS5, SNHG6, and SNHG12 lncRNA and potentially capable of interacting with one or more of these lncRNAs via competing endogenous RNA mechanism, as well as mRNAs, whose expression might be affected by the studied lncRNAs. We also investigated a possible involvement of genes for these mRNAs in oncogenesis-related processes, such as RNA processing and splicing and epithelial–mesenchymal transition. As a result of this work, four SNHG family lncRNAs with coregulation and joint putative biological functions in the pathogenesis of OC were identified.

Recently, more and more data have been accumulating indicating the role of long noncoding RNAs (lncRNAs) in the regulation of biological processes in cells, as well as in the mechanisms of cancer development and progression. Aberrant methylation of promoter regions of both protein genes and lncRNA genes can disrupt their expression and functional activity. Using bioinformatics databases, six lncRNA genes (GAS5, HOTAIR, LINC00472, LINC00886, SNHG17, and TUG1) with CpG islands differentially expressed and presumably hypermethylated in tumors of patients with ovarian cancer (OC) were selected. Using a sample of 93 OC samples, real-time methylation specific PCR showed a statistically significant (p < 0.05) increase in the level of methylation in tumors. Moreover, for the genes LINC00472, LINC00886, SNHG17, and TUG1, hypermethylation in OC was detected for the first time. Five genes (except SNHG17) showed a further increase in methylation levels at a more advanced stage, and four genes (except SNHG17 and LINC00886) showed a significant association with metastasis. Using real-time RT-PCR, differential changes in the expression level of the GAS5, HOTAIR, SNHG17, and TUG1 genes and a significant correlation of methylation with expression for the GAS5 gene were shown. Thus, hypermethylation associated with the progression and/or development of OC was detected for six lncRNA genes, which is important for elucidating the epigenetic processes involved in the pathogenesis of OC and can be used as new biomarkers of OC.

Our work aimed to evaluate and differentiate the role of ten lncRNA genes (GAS5, HAND2-AS1, KCNK15-AS1, MAGI2-AS3, MEG3, SEMA3B-AS1, SNHG6, SSTR5-AS1, ZEB1-AS1, and ZNF667-AS1) in the development and progression of epithelial ovarian cancer (EOC). A representative set of clinical samples was used: 140 primary tumors from patients without and with metastases and 59 peritoneal metastases. Using MS-qPCR, we demonstrated an increase in methylation levels of all ten lncRNA genes in tumors compared to normal tissues (p < 0.001). Using RT-qPCR, we showed downregulation and an inverse relationship between methylation and expression levels for ten lncRNAs (rs < -0.5). We further identified lncRNA genes that were specifically hypermethylated in tumors from patients with metastases to lymph nodes (HAND2-AS1), peritoneum (KCNK15-AS1, MEG3, and SEMA3B-AS1), and greater omentum (MEG3, SEMA3B-AS1, and ZNF667-AS1). The same four lncRNA genes involved in peritoneal spread were associated with clinical stage and tumor extent (p < 0.001). Interestingly, we found a reversion from increase to decrease in the hypermethylation level of five metastasis-related lncRNA genes (MEG3, SEMA3B-AS1, SSTR5-AS1, ZEB1-AS1, and ZNF667-AS1) in 59 peritoneal metastases. This reversion may be associated with partial epithelial-mesenchymal transition (EMT) in metastatic cells, as indicated by a decrease in the level of the EMT marker, CDH1 mRNA (p < 0.01). Furthermore, novel mRNA targets and regulated miRNAs were predicted for a number of the studied lncRNAs using the NCBI GEO datasets and analyzed by RT-qPCR and transfection of SKOV3 and OVCAR3 cells. In addition, hypermethylation of SEMA3B-AS1, SSTR5-AS1, and ZNF667-AS1 genes was proposed as a marker for overall survival in patients with EOC.

According to the latest global statistics for 2020, breast cancer (BC) has taken first place in the incidence of epithelial tumors, ahead of lung cancer, and is the main cause of mortality from cancer pathology among women around the world [...]

Ovarian cancer (OC) develops asymptomatically and escapes diagnosis until advanced stages, the feature contributing to a higher mortality rate. New prospects of OC diagnosis and treatment have been opened in studies of the gene regulation mechanisms that involve long noncoding RNAs (lncRNAs) and identification of the lncRNA genes that are inhibited via methylation of the promoter region. A set of 122 samples of primary OC tumors was examined by methylation specific real-time PCR to assess the methylation level of the lncRNA genes PLUT, SNHG1, SNHG6, SNHG12, and TINCR. A significant increase in their methylation levels was observed in OC (p < 0.001 by the nonparametric Mann-Whitney test). The methylation levels of SNHG6, SNHG12, and TINCR were found to correlate significantly (p < 0.05) with the stage of the tumor process, the histological grade, and metastasis. Downregulation of SNHG6, SNHG12, and TINCR was detected by real-time RT-qPCR, and a significant correlation between methylation and expression was demonstrated for SNHG6 and TINCR (r(s) <= -0.5, p < 0.001). The respective lncRNA genes were assumed to provide potential epigenetic markers of OC.

Актуальность. Рак яичников (РЯ) представляет собой группу агрессивных гетерогенных злокачественных опухолей, характеризующихся быстрой прогрессией, низким диагностическим потенциалом, высокой частотой неблагоприятных исходов и высоким потенциалом метастазирования. В последнее время все большую актуальность приобретают исследования длинных некодирующих РНК (днРНК, lncRNAs), которые не обладают способностью кодировать белки. Для днРНК характерна высокая тканеспецифичность экспрессии, они участвуют в регуляции различных сигнальных путей в клетках, демонстрируя большой прогностический потенциал при онкозаболеваниях. Цель исследования – выявление аберрантно экспрессируемых длинных некодирующих РНК в образцах опухолей больных РЯ и связи уровней экспрессии с патофизиологическими характеристиками опухолей. Методика. Образцы опухолей РЯ собраны и клинически охарактеризованы в ФГБУ «НМИЦ онкологии им. Н.Н. Блохина». Высокомолекулярную РНК выделяли из ткани стандартным методом. Анализ уровня экспрессии днРНК HOTAIR, MALAT1 и TINCR проводился с использованием ПЦР в реальном времени готовой реакционной смесью qPCRmix-HS SYBR («Евроген»). Статистический анализ уровней экспрессии выполнен в программной среде R с применением непараметрического U теста Манна–Уитни. Корреляционный анализ выполняли с использованием метода ранговой корреляции Спирмена и рассчитывали уровень его значимости. Различия считали статистически значимыми при р < 0.05. Дополнительно были проанализированы данные по экспрессии днРНК при РЯ по базе данных GEPIA (http://gepia.cancer-pku.cn/). Результаты. Анализ уровня экспрессии днРНК показал значимое (p≤0.05) снижение уровня экспрессии днРНК HOTAIR, MALAT1. При анализе образцов с учётом патофизиологических характеристик опухоли было показано, что снижение уровня экспрессии HOTAIR ассоциировано с III/IV стадией опухолевого процесса. Для днРНК MALAT1 и TINCR показана значимая корреляция низкого уровня экспрессии с развитием эндометриоидного подтипа РЯ. Заключение. Представленные данные способствуют более глубокому пониманию механизмов развития РЯ и могут быть использованы при диагностике, прогнозе и выборе тактики лечения данной патологии. Background.Ovarian cancer (OC) is a group of aggressive heterogeneous malignant tumors characterized by rapid progression, low diagnostic potential, high incidence of adverse outcomes, and high potential for metastasis. Recently, studies of long non-coding RNAs (lncRNAs), which, with rare exceptions, do not have the ability to encode proteins, have become increasingly important. LncRNAs are characterized by high tissue-specific expression and they are involved in the regulation of various signaling pathways in cells and demonstrate a great prognostic potential in cancer. Aim. Detection of aberrantly expressed long non-coding RNAs in tumor samples from OC patients and association of expression levels with pathophysiological characteristics of tumors. Methods. Samples of OC tumors were collected and clinically characterized at the N.N. Blokhin Research Institute of Clinical Oncology. High molecular weight RNA was isolated from tissue by a standard method. Analysis of the expression levels of HOTAIR, MALAT1, and TINCR lncRNA was carried out using real-time PCR and a qPCRmix-HS SYBR ready-made reaction mixture (Evrogen). Statistical analysis of expression levels was performed in the R software environment using the nonparametric Mann-Whitney U test. Correlation analysis was performed using Spearman’s rank correlation, and its significance level was calculated. Differences were considered significant at p<0.05. Additionally, expression levels of these lncRNAs in OC were analyzed using the GEPIA database (http://gepia.cancer-pku.cn/). Results. The expression levels of the HOTAIR and MALAT1 lncRNA genes were significantly decreased (p≤0.05). Analysis of the samples with the account of the tumor pathophysiological characteristics showed that the decrease in the level of HOTAIR expression was associated with stage III/IV of the tumor process. For MALAT1 and TINCR lncRNAs, low expression levels significantly correlated with the development of the endometrioid subtype of OC. Conclusion. The results of the study allow a better insight into the mechanisms of OC development and can be used for diagnosis, prognosis and selection of therapeutic tactics in this pathology.

Clear cell renal cell carcinoma (ccRCC) is the most common and aggressive histological type of cancer in this location. Distant metastases are present in approximately 30% of patients at the time of first examination. Therefore, the ability to predict the occurrence of metastases in patients at early stages of the disease is an urgent task aimed at personalized treatment. Samples of tumor and paired histologically normal kidney tissue from patients with metastatic and non-metastatic ccRCC were studied. Gene expression was analyzed using real-time PCR. The level of gene methylation was evaluated using bisulfite conversion followed by quantitative methylation-specific PCR. Two groups of genes were analyzed in this study. The first group includes genes whose expression is significantly reduced during metastasis: CA9, NDUFA4L2, EGLN3, and BHLHE41 (p < 0.001, ROC analysis). The second group includes microRNA genes: MIR125B-1, MIR137, MIR375, MIR193A, and MIR34B/C, whose increased methylation levels are associated with the development of distant metastases (p = 0.002 to <0.001, ROC analysis). Based on the data obtained, a combined panel of genes was formed to identify patients whose tumors have a high metastatic potential. The panel can estimate the probability of metastasis with an accuracy of up to 92%.

This paper introduces the reader to the field of liquid biopsies and cell-free nucleic acids, focusing on circulating tumor DNA (ctDNA) in breast cancer (BC). BC is the most common type of cancer in women, and progress with regard to treatment has been made in recent years. Despite this, there remain a number of unresolved issues in the treatment of BC; in particular, early detection and diagnosis, reliable markers of response to treatment and for the prediction of recurrence and metastasis, especially for unfavorable subtypes, are needed. It is also important to identify biomarkers for the assessment of drug resistance and for disease monitoring. Our work is devoted to ctDNA, which may be such a marker. Here, we describe its main characteristics and potential applications in clinical oncology. This review considers the results of studies devoted to the analysis of the prognostic and predictive roles of various methods for the determination of ctDNA in BC patients. Currently known epigenetic changes in ctDNA with clinical significance are reviewed. The possibility of using ctDNA as a predictive and prognostic marker for monitoring BC and predicting the recurrence and metastasis of cancer is also discussed, which may become an important part of a precision approach to the treatment of BC.