The aim of this study was to investigate the frequency and spectrum of KRAS mutations in men and women with colorectal cancer (CRC), and an impact of KRAS-mutation status on the clinical and morphological features of CRC. The study included 303 patients (168/55.4% women and 135/44.6% men) with CRC T2-4N0-2M0-1. We defined 7 KRAS SNP-mutations (G12D, G12A, G12R, G12C, G12S, G12V and G13D) located within codons 12 and 13 using Bio-Rad real-time thermal cyclers CFX96 and Real-Time-PCR-KRAS-7M Kit. The frequency of KRAS mutations was 35.6% in the CRC patients with a predominant presence of G>A transitions. The KRAS codon 12 and 13 mutations are predictive of poor prognosis The KRAS-mutated CRC has clinical features in view of the gender differences. KRAS-mutation status is a promising predictive biomarker of personalized treatment.

e23579 Background: Retroperitoneal tumors are rare heterogeneous malignant tumors. Due to their poor response to chemoradiotherapy, surgery is the main treatment option. Currently, there is little data on treatment outcomes in patients who underwent en block resection of retroperitoneal tumors and major vessels. Our purpose was to analyze surgical and oncological results in patients with retroperitoneal tumors and major blood vessel involvement. Methods: 27 patients received surgery for retroperitoneal tumors with major vessel resection in 2015-2019. Results: The mean tumor diameter was 17 cm (11-39 cm). The most frequent histological types were moderately differentiated liposarcoma (33.4%), well differentiated (18.5%), poorly differentiated sarcoma (18.5%), pleomorphic liposarcoma (22.2%), leiomyosarcoma (7.4%). Resection of the suprarenal inferior vena cava (IVC) with prosthetics was performed in 4 cases, resection of its renal segment with renal vein reimplantation - 1, resection of the infrarenal IVC with prosthetics - 8. PTFE prostheses were used as a conduit in all cases. Marginal excision of the suprarenal IVC was performed in one patient, that of the infrarenal IVC - in 5 patients; resection of the infrarenal IVC without the reconstruction - in one case. The iliac venous segment resection was required in 6 patients, in one case – with the iliac arterial segment resection and prosthetics. Macroscopic complete resection (R0-R1) was achieved in 92.6%. The postoperative morbidity was 25.9%, with no fatal outcomes. Despite the anticoagulant therapy, the frequency of thrombosis of the venous reconstruction area in the early postoperative period (1 month) was 7.4%. The median relapse-free survival was 14 months; the median overall survival was not achieved. Conclusions: Combined surgeries with simultaneous removal of retroperitoneal tumor and angioplasty demonstrate an acceptable level of morbidity and mortality. Radical removal of tumors with major blood vessel involvement allows increasing the survival in patients often considered inoperable.

e15508 Background: The most important stages of metastatic cascade are extravasation and invasion of malignant cells and their surviving in blood. The vast majority of circulating tumor cells (CTC) is destroyed by immune cells. The role of immune system which is able to play not only antitumor but also prooncogenic role is manifested both on local and systemic levels. We studied correlations between lymphocyte subsets` content in blood and in tumor of colorectal cancer patients (II, III, IV stages) with and without CTC. Methods: 60 colorectal cancer patients with II (n = 20), III (n = 20) and IV (n = 20) stages underwent surgery without previous chemotherapy. CTC were measured in blood by CellSearchSystem™ (JanssenDiagnostics, LLC), cell-mediated immunity was assessed in blood by flow cytometry (BD Canto II) and in tissue after surgery by immunohistochemistry; some markers of proliferation and epithelial-mesenchimal transition (EMT) in tumor cells (Ki-67, E- and N-cadherins) were also studied. Criteria of CTC-positive and CTC-negative samples were > 3 and ≤3 respectively. Correlative analysis was performed between the data of the patients with and without CTC in each stage, r was counted. Results: In CTC-positive patients with all the stages the number of strong and moderate correlations between system immunologic factors involving CD8+ appeared to be fewer than in CTC-negative ones (7 vs 19). On the contrary, the number of correlations with T regs in CTC-positive was increased: 5 vs 3 in CTC-negative patients. In patients with CTC > 3 fewer correlations were noted between factors of local and systemic immunity than in CTC-negative ones (9 vs 4 in II stage) and total disruption of all the correlations between system immunologic factors and proliferating tumor cells in III and IV stages was established. Some pathologic correlations appeared in CTC-positive patients like moderate direct one between activated T-lymphocytes` amount and Ki-67+ tumor cells. The number of correlations between intratumoral lymphocytes and tumor cells expressing proliferation and EMT markers in CTC-positive patients was decreased in comparison with CTC-negative ones (4 vs 10 in II stage, 1 vs 9 in III, 2 vs 9 in IV stage). Conclusions: The presence of CTC in colorectal cancer patients rather than tumor stage is associated with imbalance of their systemic and local immunologic factors. This provides some evidence that disruption of interactions in the immune system is at least partly due to CTC.

e15531 Background: High incidence and mortality rates of gastric cancer cause a constant search for the most informative and effective methods of diagnosis and treatment assessment. In this regard, studying the expression of markers with the stem phenotype in primary tumor tissues in patients with gastric cancer with and without metastases is of undoubted interest. Methods: The study included 20 gastric cancer patients aged 30-80 years: group 1 – gastric cancer T3-4аN0-3M0 (G2) without metastasis (58.9±9.7 years); group 2 – gastric cancer T3-4аN0-3M1 (G2) with peritoneal metastasis (53.4±11.9 years). Immunohistochemical study was performed on paraffin-embedded tumor tissue sections using mouse monoclonal antibodies to CD44 (156-3С11 Thermo Scientific) at a 1:2500 dilution and rabbit polyclonal antibodies to CD133 (Cloud-Clone Corp.) at a 1:700 dilution; the Thermo Scientific autostainer was used for staining. Membrane staining and staining intensity were assessed: 0, 1+ weak, 2+ moderate, 3+ strong staining. Positive expression was defined as ≥10% cut-off for CD44 and ˃5% for CD133. Results: Positive expression of CD44+ was detected in 67% (13) in group 2 vs. 20% (4) in group 1. In the metastatic group, the number of cells that stained positive for CD44 expression ranged from 9 to 15%, on average 10.0±3.08%, without metastases – from single cells to 13%, on average 6.0±2.3%. A chi-square test showed statistically significant association in the groups (8.256 at p = 0.004). Positive CD133+ expression in tumor tissues was registered in 100% (20) in group 2 and 80% (16) in group 1. The range of positively stained cells in group 2 was from 10 to 40%, on average 21.3±11.6%, in group 1 - from single cells to 14%, on average 10.0±2.4%. A chi-square test showed statistically significant association in the groups (4.444 at p = 0.036). Conclusions: Immunohistochemical study of the selected tumor cell markers in gastric cancer revealed some characteristics of their expression depending on the presence of metastases. The results can be the basis for further research for the most complete characterization of a heterogeneous tumor population in gastric cancer and the role of individual cells in the tumor growth, progression and metastasis.

The article provides a modern vision of the problem of cardiotoxicity in oncology. Integrity and generality of nodal pathogenetic events in the body in case of carcinogenesis, antitumor therapy and cardiopathology are caused by similar mechanisms at different hierarchical levels. Identity of potential risk factors, including inflammation, aging, obesity, diabetes and smoking, has been noted. Similarly, in the development of metabolic syndrome and carcinogenesis, the level of growth factors (IGF-1), neoangiogenesis, hormones and other triggers of oncological and cardiovascular pathology is increasing. It is important that a variety of clinical manifestations of cardiotoxicity are due to the rapid expansion of the number of therapeutic options for effects. This thesis is illustrated by vivid examples of the use of anthracycline-based drugs whose mechanism of action is aimed at damaging genetic targets. The use of monoclonal antibodies -trastuzumab, is directed against HER2 / ErB2 receptors in breast cancer and is accompanied by distinct signs of cardiotoxicity especially in the elderly. A new strategy to enhance the targeted cytotoxic immune response to cancer cells (Ipilimumab, Nivolumab) has a chance to cause autoimmune myocarditis and myositis. Modern anti-angiogenic methods of cancer therapy, including inhibition of VEGF, significantly increase the risk of myocardial ischemia, hypertension and atherosclerosis. This indicates the need for monitoring of complications, a targeted selection of preventive and curative strategies, as well as attention to the mechanisms of tissue homeostasis in the implementation of the antitumor effect.

e13525 Background: Cancer is a disease characterized by uncontrolled cell proliferation. DNA replication is the main driving force behind cell proliferation in both normal development and cancer. Non-coding Y-RNAs are important factors in initiating DNA replication in the nuclei of human cells. Excessive expression of Y-RNA is characteristic of tumors of the bladder, cervix, kidney, lung and prostate. It has also been shown that the level of small RNAs formed from the 3'- and 5'-ends of Y-RNA is significantly higher in patients with certain types of cancer compared to healthy people, therefore, these RNAs may have diagnostic value. However, for colon tumors, data on the expression of Y-RNA/YsRNA obtained in previous studies are ambiguous. The aim of the study was to analyze the differential expression of YsRNA in the tumor and non-tumor tissue of patients with CRC using next generation sequencing (NGS). Methods: For NGS, 10 patients with CRC (colon adenocarcinoma, G2). were selected. Small RNA fractions were isolated using the mirVana miRNA Isolation Kit protocol (Ambion, Life Science Technologies, USA). The library was prepared for sequencing using the TruSeq Small RNASample Preparation Kit (Illumina, USA). Sequencing of the nucleotide sequences of cDNA libraries was performed using a MiSeq (Illumina, USA). The determination of the copy number of Y-RNA fragments (YsRNA, 19-34 bp) was carried out by comparing the nucleotide sequence of the sequenced molecules in each sample with the known nucleotide sequences presented in the databases. In the analysis of differential expression, the edgeR method, implemented in the R language, was used. Results: Several different fractions of YsRNA were detected in tumor and non-tumor tissues: hY3sRNA (the most represented fraction, more than 70%), hY5sRNA and hY1sRNA. In tumor tissue relatively non-tumor, a statistically significant (p < 0.001) increase of 4 and 6 times the number of copies of hY3sRNA and hY5sRNA, respectively, was detected. The function of YsRNA in tumor and normal cells has not yet been established. Conclusions: Thus, in the tumor colon tissue differential expression of 2 YsRNA fractions - hY3sRNA and hY5sRNA, was detected. These YsRNAs can become promising tumor markers and targets for the treatment of CRC, as well as make certain contributions to understanding the mechanisms of carcinogenesis in this nosology.

e15500 Background: The immune response plays a key role in the oncogenesis of colorectal cancer. The heterogeneity of the tumor environment determines the need for immunogenetic profiling to identify associations with the implementation of tumor-specific immune responses in colorectal cancer. The purpose of our study was to describe the expression profiles of miRNAs and genes involved in the regulation of the immune response in colorectal cancer. Methods: The study included 18 patients (median age 66 years) diagnosed with colorectal cancer who were treated at the National Medical Research Centre for Oncology in 2018-2019. Total RNA was isolated using TRIzol (Thermo Fisher, USA) followed by treatment with DNase 1 (ThermoFisher, USA). Sequencing of RNA samples was performed using two approaches: AmpliSeq for Illumina Immune Response Panel (Illumina, USA) and TruSeq Small RNA Library Prep Kit -Set A (Illumina, USA) according to the manufacturer's instructions on a NextSeq 550 device (llumina, USA). Results: The study revealed 168 differentially expressed genes and 46 differentially expressed miRNAs (p < 0.05). 29 miRNA-mRNA pairs were identified. It has been established that the key signaling mechanism involved in the regulation of the tumor-specific immune response is chemokine signaling pathway (hsa04062). Expression of the CXCL1 and CXCL10 genes encoding the chemokines of the same name is increased in tumor cells (logFC = 1.51, p = 0.006 and logFC = 2.67, p < 0.001, respectively). At the same time, the level of hsa-miR-30a-5p and hsa-miR-99b-5p, which negatively regulate the expression of CXCL1 and CXCL10, is decreased (logFC = -2.26, p < 0.001 and logFC = -1.57, p < 0.001). Conclusions: Activation of expression CXCL1 and CXCL10 with simultaneous loss of negative regulators hsa-miR-30a-5p and hsa-miR-99b-5p was determined in colorectal tumors by NGS-sequencing, which seems promising for the development of personalized therapy, based on the immunogenetic features of colon tumors.

e16104 Background: Cancer-testis antigens (CTAs) can be used for immunotherapeutic approaches and early detection of malignant tumors. Despite numerous studies of CTA expression in various tumors, including colon tumors, the mechanisms of transcriptional activity regulation in colorectal cancer (CRC) remain poorly studied. One of the possible mechanisms of regulation of gene expression is a change in their copy number (CNV). The aim of the study was to analyze the changes in the copy number and expression of CT-genes in patients with CRC. Methods: Tumor and normal colon tissues of 81 patients were used in the study. DNA was isolated by phenol-chloroform extraction. RNA was isolated by the Chomczynski&Sacchi method (2006). The REVERTA-L reagent kit was used for the cDNA synthesis. Determination of expression and copy number of 16 CT genes ( MAGE-A1, -A2, -A3, -A4, MAGE-B1, -B2, GAGE-1, -3, -4, MAGEC1, BAGE, XAGE3, NYESO1, SSX2, SCP1, PRAME1) was performed using the Real-Time qPCR method (reference genes - GAPDH and GUSB). Differences were evaluated using the Mann-Whitney test, correlation analysis - using Spearman's rank correlation coefficient (r). Results: An analysis of CT-gene expression and CNV in tumor and normal colon tissues (n = 81) revealed a statistically significant (p < 0.05) difference between these parameters in tumor tissue relative to normal one: for MAGEB1 an increase of 2.0 and 2.7 times, GAGE3 an increase of 2.0 and 2.5 times, GAGE4 decreased by 5.0 and 6.8 times, BAGE decreased by 2.4 and 1.7 times, SSX2 increased by 1.8 and 2.1 times, SCP1 increased copy number by 4.4 times and PRAME1 increased expression and copy number by 2.9 and 2.3 times, respectively. When comparing CNV and expression of 16 CT genes, a positive correlation was observed (r = 0.875). Conclusions: Thus, the aberrant expression of MAGEB1, GAGE3, GAGE4, BAGE, SSX2 and PRAME1 found in the tumor tissue of CRC patients depends on the copy number of these CT-genes.