Marker-adjusted personalized chemotherapy of breast cancer G.P. Guens, 1* N.I. Moiseeva, 2 O.G.Ovsii, 1 E.Y. Rybalkina, 2 A.A. Stavrovskaya 2 1 – Department of Oncology and Radiology, Moscow State University of Medicine and Dentistry 2 – N.N. Blokhin Russiаn Cancer Research Center, Russian Academy of Medical Sciences SUMMARY Aims: searching ways for individualization of chemotherapeutic treatment in breast cancer patients by means of: 1. Evaluation of the efficacy of chemotherapy CAF/AC in various biological subtypes of breast cancer; 2. Evaluation of prognostic significance of expression mRNA YB-1 in this cohort. Materials and Methods: 510 breast cancer patients, stages I-III, among them 277 patients who underwent chemotherapy; mRNA YB-1 expression was evaluated by semi-quantitative RT-PCR. Results: the effectiveness of chemotherapy depends on the tumor molecular subtypes. CAF/AC chemotherapy regimen is not effective in luminal A subtype and is effective in triple-negative subtype of tumors. Evaluation of the expression of mRNA YB-1 in breast tumors helps to select a group of patients with worse prognosis (р=0.03) and can serve as an additional prognostic factor. This prognostic factor is not associated with molecular subtypes of breast cancer. Key words: breast cancer, efficacy of chemotherapy, molecular subtypes, prognostic factors, YB-1 Contacts: Gelena Guens, e-mail: gelena974@gmail.com Alla Stavrovskaya, e-mail: astavrovskaya@yahoo.com 1. INTRODUCTION Breast cancer (BC) is the most common cancer among women in Russia [1]. One of the main treatment methods of BC is systemic chemotherapy (CT). Most of CT regimens include anthracyclines. However the question about individualization CT remains critical [2, 3]. Perou C.M. et al. [4] have studied samples of breast tumors and proposed of classification of BC based on pattern variation of genes expression. Nowadays this classification is constantly improving. Now in routine practice used immunohistochemical surrogate markers: estrogen receptors (ER), progesterone receptor (PR), HER2/neu, index of proliferation Ki67 [3]. The objective of our study was to find the approaches of making CT more individualized: to study the efficacy of anthracycline-based chemotherapy regimen in different molecular subtypes of BC and to determine prognostic significance of mRNA YB-1 expression in breast cancer tissue.