SNAI1 and cancer: The culture of human breast cancer cell lines (MCF7 and BT-549) for more than 7 days in cancer stem cell medium promotes the formation of tumourspheres associated with increased expression of mesenchymal markers (VIMENTIN, N-CADHERIN, SNAIL) as well as PD-L1 [535], supporting that mechanisms predisposing to immune evasion can be monitored in relatively short experiments.