Аннотация:Background: The purpose of the study was to assess changes in biochemical markers of cardiotoxicity in anthracycline chemotherapy for breast cancer. Methods: The study included 30 pts (32-72 years, 50%<50 years) with stage II-III breast cancer (BC) receiving 4 cycles of anthracycline (AC) chemotherapy (CT). N-terminal pro-brain natriuretic peptide (NT-proBNP), troponin I (TI), creatine kinase (CK), creatinine and urea were determined (Vitros 5600, USA) in the blood serum before AC administration and on days 2 and 5 after it. The results were compared with electrocardiography and echocardiography (EchoCG) data. The data were processed using the Statistica 6.0 program. Results: No clinical or instrumental data on an acute myocardial infarction were registered. NT-proBNP˃64.0 pg/mL was considered as high. Before treatment, 15 (50%) pts showed increased NT-proBNP (on average 144.3±38.8 pg/mL), which correlated with EchoCG results and indicated initial cardiovascular pathology. The initial level of NT-proBNP in other pts was 48.2±14.7 pg/mL. Correlation between the age and NT-proBNP was not found (p > 0.05). Day 2, NT-proBNP increased by 2.6 times (p < 0.01) in 26 (86.7%) pts: 15 (50.0%) with initially high levels and 12 (40.0%) with initially normal ones. Day 5, NT-proBNP increased in 7 (23.3%) pts and decreased in 6 (20.0%). NT-proBNP levels restored to initial values by the 4th CT cycle. The changes after the 1st AC injection and on days 2 and 5 were similar in direction. TI and CK did not change at all stages even in pts with high NT-proBNP, indicating the development of reversible cardiotoxic effect. Levels of creatinine and urea were within the reference range which excluded their impact on NT-proBNP. Conclusions: NT-proBNP is bound to be the most sensitive marker of cardiotoxicity and could serve as an earlier marker in patients with breast cancer undergone chemotherapy with anthracyclines.