(IMAGE) Max-Planck-Gesellschaft Caption These images show a tumor cell penetrating the endothelial barrier. In the image on the left, the green-stained tumour cell has succeeded in penetrating the red-stained endothelial barrier. In the image on the right, in contrast, the tumor cell remains within the blood vessel whose endothelial cells lack the P2Y2 receptor, unlike those in the image on the left. The cell nuclei are stained blue. Credit MPI f. Heart and Lung Research Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.