PECAM1 and breast cancer: Counting of intratumoural blood vessels in highly vascularised areas of mammary tumours showed significantly (approximately 20%) less CD-31-positive structures in the PyMT;Col15a1−/− tumours than in the PyMT control tumours on average, potentially indicative of impaired tumour angiogenesis in the absence of the perivascular vessel stabiliser ColXV [10,11].