The endothelium plays an important role in cancer metastasis, but the mechanisms involved are still not clear. In the present work, we characterised the changes in endothelial function at early and late stages of breast cancer progression in an orthotopic model of murine mammary carcinoma (4T1 cells). Endothelial function was analysed based on simultaneous microLC/MS-MRM quantification of 12 endothelium-related biomarkers reflecting glycocalyx disruption [syndecan-1 (SDC-1), endocan (ESM-1)], endothelial inflammation [vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), E-selectin (E-sel)], endothelial permeability [fms-like tyrosine kinase 1 (FLT-1), angiopoietin 2 (Angpt-2)], haemostasis [von Willebrand factor (vWF), tissue plasminogen activator (t-PA), plasminogen activator inhibitor 1 (PAI-1)] and others pathophysiologically linked to endothelial function [e.g. adrenomedullin (ADM), adiponectin (ADN)]. The early phase of metastasis in mouse plasma was associated with glycocalyx disruption (increased SDC-1 and ESM-1), endothelial inflammation (increased sVCAM-1) and increased vascular permeability (Angpt-2). During the late phase of metastasis, additional alterations in haemostasis (increased PAI-1 and vWF), as well as a rise in ADM and substantial fall in ADN concentration were observed. In conclusion, in a murine model of breast cancer metastasis, we identified glycocalyx disruption, endothelial inflammation and increased endothelial permeability as important events in early metastasis, while the late phase of metastasis was additionally characterised by alterations in haemostasis.