Pridko O.S.1, Rishko M.F.2, Rusyn A.V.1

Hormonal therapy is one of the main methods of comprehensive treatment for patients with locally advanced breast cancer (BC). Despite the intensity of studies devoted to the search for markers associated with the aggressiveness of the tumor process, today there is no unified point of view regarding the prognostic value of the proliferative activity of neoplasms in patients of this category. Aim: to investigate the features of Ki-67 expression in tumor cells of patients with hormone-dependent breast cancer who received neoadjuvant hormone therapy (NGT), and to find out the significance of this protein for predicting the aggressiveness of the tumor process. Object and methods: the study was conducted on the clinical material of 110 patients with stage II-III breast cancer who were receiving inpatient treatment at the Transcarpathian Antitumor Center during 2011–2020. All patients included in the study received NGT (tamoxifen or letrozole in mono-mode). The effectiveness of NGT was evaluated according to the data of mammography and ultrasound diagnosis of mammary glands according to RECIST 1.1 criteria. The study of Ki-67 expression in breast cancer cells was performed on paraffin sections of surgical material using the immunohistochemical method. Statistical processing of the obtained results was performed using the GraphPad Prism v.6.05 program, considering the nature of the distribution of the obtained data. Results: it was discovered that a positive effect was most often determined with the use of letrozole in the neoadjuvant regimen compared with the use of tamoxifen (75.0 vs. 60.0% of cases). High levels of Ki-67 expression in tumor cells were identified in patients with NGT-resistant neoplasms, which are characterized by stabilization and progression of the tumor process. It was shown that the 3-year recurrence-free survival of patients with hormone-dependent breast cancer treated with tamoxifen and letrozole in the neoadjuvant regimen was higher in the presence of a low level of expression of Ki-67 in tumor cells. Conclusion: it has been substantiated that the possibility of using Ki-67 expression indicators in tumor cells for predicting the aggressiveness of the course of hormone-dependent breast cancer and planning individualized treatment tactics.

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