RÉSUMÉ
SUMMARY OBJECTIVE: Breast cancer is among the highest causes of morbidity and mortality in women. Trastuzumab therapy, which is known to be significantly cardiotoxic, is mainly used to treat patients with resistant breast cancer, including estrogen receptor-positive type. We aimed to show the effects of trastuzumab therapy on endothelial functions of breast cancer patients. METHODS: In this study, a total of 26 participants (24 female and 2 male patients, minimum age: 38 years, maximum age: 79 years, and mean age 57.3±12.7 years) were enrolled in the study. For the statistical evaluation of data, we classified the participants of the study as follows: Pretreatment: Before trastuzumab therapy; Treatment Period 1: 1 month after the first dose of trastuzumab; Treatment Period 2: 4 months after the first dose of trastuzumab; Treatment Period 3: 12 months after the first dose of trastuzumab. We conducted repeated-measures analysis of variance (Greenhouse-Geisser) and paired-sample t-tests to statistically compare the groups using flow-mediated dilation measurements. RESULTS: We determined that there are statistically significant differences between flow-mediated hyperemia and ratio values (flow-mediated dilation) of the groups (p<0.009 and p<0.001, respectively). CONCLUSION: Our data indicate that trastuzumab therapy could have negative effects on endothelial functions in breast cancer patients.