Background: Endocan, known as endothelial cell specific molecule (ESM), is a novel endothelial dysfunction marker. The aim of this study is to examine the plasma endocan level and its prognostic significance in newly diagnosed breast cancer patients. Methods: A total of 84 patients were enrolled the study. Plasma endocan level was measured by specific enzyme-linked immunosorbent assay (EL_ISA) kit. Ethical approval and informed consent were attained. Results: At the time of diagnosis, 33 patients had stage 4 disease. The median plasma endocan level was 619.9 (min 259.9e2813.2) ng/L and its level was significantly higher in metastatic breast cancer group compared to nonemetastatic breast cancer group. According to molecular sub-type of breast cancer, there is not statistical difference in plasma endocan level, but its level was higher in patients with Her-2 amplified and triple negative breast cancer (TNBC). Median follow-up time is 11 (1-30) months. Event free survival (EFS) was 15 months in patients with plasma endocan level lower than 620, while it was 4 months in patients with serum endocan level greater than 620 (p ¼ 0.016). There was no difference between groups in terms of hypertension, age, Lymphovascular invasion (LVI), extra capsular extension (ECE), body mass index (BMI) and White blood cells (WBC), platelet count and plasma endocan level. Conclusion: Plasma endocan levels higher than non metastatic breast cancer. Patients with high plasma endocan levels are short EFS. Further studies would be useful to assess endocan level as a prognostic factor in breast cancer.