In the cerebral endothelial cell invasion assay, we found that Tim3 knockdown in both MCF-7 and MDA-MB-231 resulted in a significantly reduced invasion of the breast cancer cells through the endothelium (31±8 vs 24±8 for MCF7, p=0.018; 211±48 vs 142±54 for MDA-MB-231, p<0.001, WT and Tim3kd respectively)...Tim3 has a marked influence on the barrier functions, adhesiveness and the sensitivity to docetaxel of breast cancer cells. Loss of Tim3 in breast cancer cells reduces tumour cell's penetration of cerebral endothelium.