CD31 expression by cells of extensive ductal in situ and invasive carcinomas of the breast

CD31 is a surface molecule mediating homo- and heterotypic interactions that control leukocyte trafficking through the endothelial layer. Monoclonal antibodies against CD31 are used as markers of neovascularization. Assessment of angiogenesis in 270 breast carcinomas revealed expression of CD31 in a single case of large (5.2 cm in diameter) high nuclear grade ductal carcinoma, in both in situ and invasive components. Expression was limited to the cell membrane, suggesting an adhesion function of CD31 in epithelial cells. At variance with invasive breast carcinomas, angiogenesis is not considered as a prognostic parameter in DCIS, and consequently anti-CD31 MoAb are not included in standard testing. Thus, a reasonable explanation for our finding was that CD31 expression might be underscored in DCIS cells. Therefore, we focused on 32 ductal carcinomas in situ (DCIS) larger than 2 cm, pure or associated with invasive ductal carcinoma (IDC). Cancer cells of seven extensive, high nuclear grade DCIS associated with IDC were CD31⁺. CD31 was expressed by cells of DCIS the were able to colonize lobules and large ducts extending to the nipple (Paget's disease). It was also expressed by IDC, but only in association with CD44. Normal epithelium and hyperplastic epithelial lesions were consistently CD31^-. We conclude that CD31 expression is a feature acquired by breast cancer cells in DCIS model. Secondly, CD31 expression mainly correlates with tumor cell spreading within the ductal system; and, finally, the invasive phenotype requires the coexpression of CD31 and CD44.