Prognostic role of syncytin expression in breast cancer.

Breast cancer cells were recently found to produce syncytin, an endogenous retroviral protein implicated in cell fusion, immune regulation, and nitric oxide synthase expression. To determine whether syncytin has a prognostic role in breast cancer, we investigated a series of 165 premenopausal lymph node-negative women for syncytin expression using an immunocytochemical scoring system. Results were analyzed with the Kaplan-Meier method and with the Cox proportional hazard model. Syncytin expression was observed in 38% of the patients, and the degree of syncytin expression constituted a positive prognostic indicator for recurrence-free survival. In addition, we examined a second series of 54 consecutively operated breast cancer patients of all categories and the results supported the conclusions made from the first study. Thus, syncytin expression constitutes a positive prognostic factor in breast cancer--a phenomenon that may be related to the involvement of syncytin in mediating fusions between breast cancer cells and endothelial cells.