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The occurrence of TР53 gene mutations and loss of heterozygosity in diffuse large B-cell lymphoma in the dependence of rs1042522 genotype

Introduction. Recent studies have shown that in tumor cells of various types of malignant neoplasms, in carriers of the heterozygous variant rs1042522 of the TP53 gene, most of the point mutations are detected in the G allele of the gene, while the C allele was lacking as a result of loss heterozygosity (LH). At the same time, the association of the G allele of the rs1042522 gene with a decrease in the effectiveness of therapy in patients with malignant neoplasms was described. Previously, the study of rs1042522 on samples of patients with lymphomas was carried out only in healthy tissues; in the tumor tissue of diffuse large B-cell lymphoma (DLBCL), this single nucleotide polymorphism was not studied. Given the propensity of B-lymphocytes to p53-mediated apoptosis, the study of the rs1042522 genotype in combination with somatic aberrations, such as mutations or LH of the TP53 gene in the tumor tissue of DLBCL is of particular interest. Aim. To describe the frequency of occurrence of somatic mutations and LH in the TP53 gene depending on the rs1042522 genotype in the tumor tissue of patients with DLBCL. Materials and methods. The study included 150 patients with a diagnosis of DLBCL confirmed histologically and immunohistochemically. DNA was isolated from paraffinized blocks of tumor lymph nodes and extranodal lesions by phenol-chloroform extraction using guanidine. Genotyping according to rs1042522 and detection of cases of loss of heterozygosity in the TР53 gene was carried out by PCR with the analysis of polymorphism of the lengths of restriction fragments. Confirmation of LH and the search for mutations in the TP53 gene were carried out by direct Sanger sequencing. Results. In the study group, almost a third (28.6%) of patients with DLBCL at the stage of tumor diagnosis had genetic anomalies in the structure of the TР53 gene (LH and mutations). The combination of LH and the mutant status of this gene in patients with heterozygous Arg/Pro genotype of the tested polymorphism in the tumor tissue was not revealed. At the same time, it was noted that in a subgroup of 73 samples with a homozygous G/G genotype, mutations were detected in 20 cases (27.3%). In the subgroups of C/C homozygous and G/C heterozygous samples, the mutation was detected only in 1/13 (7.7%) and 4/64 (6.25%) cases, respectively. The significance of differences in the frequency of detection of mutations between G/G homozygous patients and other patients with DLBCL (genotypes C/C+G/C) was p < 0.001, and the probability of detecting mutations in the TР53 gene in carriers of the G/G genotype was more than 5.4 times higher than that in carriers of other genotypes (odds ratio – 5.4, 95% confidence interval – 1.9; 15.4). Conclusion. In order to increase the probability of identifying of combined detection of LH and mutations in TP53 with different rs1042522 genotypes, it is possible to increase the number of lymphoma samples, as well as the use of high-performance sequencing and methods for searching for allelic imbalance, which will allow registering the loss of heterozygosity in homozygous samples as well. A possible direction for further research may also be the analysis of the clinical significance of the combined detection of the homozygous genotype G/G of the marker and LH or/and somatic mutations in the TP53 gene in the tumor tissue of patients with lymphoma.