Identification of major mutation in genes of hereditary predisposition to breast cancer in patients of the Republic of Crimea

The most common oncopathology among the female population is breast cancer (BC). Hereditary breast cancer is characterized by an autosomal dominant type of inheritance with high penetrance, early age of the onset and pronounced genotypic and phenotypic heterogeneity. Taking into account syndromic pathology, hereditary breast cancer can be associated with mutations in the genes: TP53, MLH1, MSH2, PTEN, NBS1, ATM, BRIP1, RAD50, BLM, FGFR2, etc. This malignant neoplasm, along with other hereditary oncopathologies, is also caused by the presence of mutations in candidate genes, such as BRCA1, BRCA2, CHEK2 and PALB2, particularly. In the last four genes, according to the oncaBRCA database (, noted is the largest number of pathogenic mutations, and therefore they have been selected for our study [1]. Taking into account the analysis of global data, our own criteria for inclusion in risk groups are applied as follows: a family history of cancer (2 or more cases of breast cancer in relatives of the 1st and 2nd degree of kinship, especially breast cancer at the age under 50 years, bilateral manifestation of cancer, primary multiple malignant neoplasms, hereditary oncological syndromes: all these are clinical signs of hereditary breast cancer. The question of the nature of the mutation c.470T> C in the CHEK2 gene remains relevant. Namely, there is data showing that this mutation in a number of European countries and the USA is associated with an increased risk of developing breast cancer; in some countries of North America and the Czech Republic, researchers refute this hypothesis; in some populations of China, Iran, Great Britain, Yakutia (Russia), this genetic variant has not been detected at all [3]. In Russia, it has been shown that the mutation c.470T> C in the CHEK2 gene is not associated with an increased risk of developing breast cancer [2], however, in connection with 40 | Cardiometry | Issue 33. November 2024

the availability of data from foreign studies indicating that there is an association with an increased risk of developing breast cancer, this issue is a pressing task.

The aim of the study: to determine the frequency spectrum of mutations in the genes of hereditary predisposition to breast cancer BRCA1, BRCA2, CHEK2 and PALB2 in patients with clinical signs of breast cancer in the Slavic population and the Crimean Tatar population of the Republic of Crimea and determine the association of the identified major mutation with an increased risk of breast cancer.

MATERIALS AND METHODS

Mutations in the candidate genes of breast cancer were studied as given below: BRCA1 (c.5266dupC, c.181T>G, c.5251C>T, c.4035delA, c.5161C>T, c.4675G>A, c.68_69del, c.3700_3704del, c.1961de-lA), BRCA2 (c.3749dupA, c.961_962insAA), CHEK2 (c.470T>C, c.1100delC, c.444+1G>A, c.893_897del), PALB2 (c.1592delT). The material was whole blood of patients with clinical signs of breast cancer admitted to the State Healthcare Institution of the Republic of Crimea “Crimean Republican Oncology Clinical Institution named after V.M. Efetova”, and a reference group of patients with no family history of malignant neoplasms, admitted to Genesis Clinic LLC (oncology department). Applied were the following research methods: DNA extraction from whole blood of patients with spin columns using the ExtractDNA Blood kit, Eurogen, Russia; measurement of the concentration of isolated DNA with a fluorimeter, using the QuantiFluor® dsDNA System kit, Promega, USA; carrying out real-time PCR with melting curve detection using the HRR-screening kit, Testgen, Russia. The real-time PCR was performed with a LightCycler 96 amplifier (Roche), as well as DTprime (DNA-tech-nology). The study design consisted of a case-control study: collected was a database of certified DNA samples of patients with clinical signs of breast cancer and a reference group of patients without a family history of malignant neoplasms of the Slavic and Crime- an Tatar populations of the Republic of Crimea. The real-time PCR was performed to detect mutations in the genes of hereditary predisposition to breast cancer BRCA1/2, CHEK2 and PALB2 using all DNA samples taken for the study. Statistical processing of the results was carried out using the Fisher criterion, where p is the achieved level of significance.

RESULTS OF THE STUDY

As a result of the study, we analyzed the certified DNA samples of 111 patients with clinical signs of hereditary breast cancer: 87 patients of the Slavic population and 24 patients of the Crimean Tatar population versus 44 patients of the reference group (patients without a family history of malignant neoplasms, including breast cancer): 27 of the Slavic and 17 of Crimean Tatar origin.

We identified 7 genetic variants in the DNA of 24/111 (21.6%) patients with clinical signs of hereditary breast cancer and 1 mutation in 3/44 (6.8%) DNA of patients of the reference group in both ethnic populations. In the female patients of Slavic ethnicity, the following mutations were detected: in the CHEK2 gene c.470T>C (the most common variant) with a predominance in patients with an increased risk of breast cancer: 11 carriers (12.6%) and 2 carriers (7.4%) in patients of the reference group [hereinafter referred to as the rate of occurrence of mutations in DNA of patients with an increased risk of breast cancer] in the BRCA1 gene: c.5266dupC – 5 carriers (5.7%); c.1961delA – 2 carriers (2.3%); and four mutations c.4675G>A, c.3700_3704del, c.5251C>T, c.181T>G each were found in 1 carrier (1.1%). In one patient of Slavic ethnicity with an increased risk of breast cancer, two mutations were detected at the same time: in the CHEK2 gene c.470T>C and BRCA1 c.5266dupC.

In patients of the Crimean Tatar ethnicity of the Republic of Crimea, the following mutations were identified: in the CHEK2 gene c.470T>C (the most common variant) with a predominance in patients with an increased risk of breast cancer as listed below: 2 carriers (8.3%) and in patients of the reference group - 1 carrier (5.9%); [hereinafter referred to as the rate of occurrence of mutations in the DNA of patients with an increased risk of breast cancer] in the BRCA1 gene c.1961delA - 4.2%. Mutations in the BRCA2 and PALB2 genes were not detected in patients with clinical signs of hereditary breast cancer in the Republic of Crimea. The calculations has shown that the statistical significance of the actual results is higher than the significance level for medical research and is p= 0.168.

CONCLUSION

Thus, in the Republic of Crimea, among both the Slavic and Crimean Tatar populations, the major mutation is the c.470T>C mutation in the CHEK2 gene. However, after examining the reference group of patients and calculating the statistical significance of the results, it has been shown that the presence of the c.470T>C mutation in the CHEK2 gene is not associated with an increased risk of breast cancer in patients with clinical signs of breast cancer. This fact is consistent with some earlier studies, which have not found an association between the presence of this mutation and an increased risk of breast cancer in BC patients in Russia. However, due to the presence of such an association in world populations, the sampling should be expanded to obtain the most accurate results. Thus, the question of the association of the c.470T>C mutation in the CHEK2 gene with an increased risk of breast cancer remains open. It should also be remembered that the CHEK2 gene is a gene of medium penetrance and the absence of a clinical picture in patients and their immediate relatives from the control group can be explained by this fact.