PECAM1 and ductal breast carcinoma in situ: In contrast to CD31 staining, endoglin was not expressed in normal breast ECs, but was expressed by ECs in 17% of UDH cases, 19% of ADH cases, 21% and 44% of DCIS cases (low/intermediate grade and high grade, respectively) and in 84% of invasive carcinomas (Figure 1D).