In addition, when we visualized tumor vessels by immunostaining of breast cancer for the endothelial marker CD31, we noticed that vessels diameter but not number of vessels was reduced in the MDA-MB-231 OPA1−/− tumors (Fig. 4e-g). These data suggested the possibility that acute OPA1 inhibition can counteract tumor growth. This evidence concerns the gene PECAM1 and breast carcinoma.