During the process of metastasis, cancer cells are detached from the primary tumour and may find their way into the blood system, from where they can migrate in a distant site. Endothelial cells line the vascular wall of all blood and lymphatic vessels and regulate its permeability for substances and migratory cells. Previous studies have focused on the properties of cancer cells (Abidine et al. 2018), as well as their interaction with endothelial cells (Rajan et al. 2016), as they attach to and transmigrate through the endothelium barrier. For many authors, the most widely accepted hypothesis was that transmigration is a characteristic of cancer cells, overlooking the possibility of endothelial cells actively participating in this process (Mierke et al. 2012). In this paper, endothelial monolayers were studied with a previously developed AFM microrheology technique (Abidine et al. 2018) when cultured in cancer cell conditioned medium, at different dilutions. This medium is enriched with molecules secreted by the cancer cells, which may play a role during the cancer cells’ migration and alter the endothelial cells’ behaviour (Ritchie et al. 2021). We show the first results of the viscoelastic properties of endothelial cells under these experimental conditions.