Quantification of the number of CD31 and aSMA positive blood vessels in various tissues (vessel density) showed that in both intraperitoneal and subcutaneous endometriosis, the number of CD31 vessels largely exceeded the number of aSMA positive vessels, whereas in the eutopic endometrium (inside the uterus) and the muscular tissue of the abdominal wall adjacent to the endometriosis lesions (peri-endometriotic tissue) or distant from the lesions, equal numbers of CD31 and aSMA positive vessels were observed (Figure 6A). Here, PECAM1 is linked to endometriosis.