Epstein-Barr Virus (EBV) is well understood as an oncogenic virus in human tumors. Its association with breast cancers has been reported but is still in controversy. So we have examined the expression of EBV in breast cancers and evaluated the relationship between the well-known prognositc factors of breast cancer and EBV expression.

A retrospective study was conducted with patients who had been re-evaluated to confirm the diagnosis based on immunohistochemical analysis with EBNA-2 expression, between January 1991 and December 2002. The cases were assigned to the positive lesion that displayed 10% or more of immunoreactive cells.

The expressions of EBNA-2(Ebstein Barr virus nuclear antigen - 2) were noted in 26 (21.1%) out of 123 cases of breast cancer patients and 4 (20%) out of 20 cases in a control group of benign tumors. The expression of EBV in breast cancers and that of a control group were not different significantly. But, the correlation between the expression of EBNA-2 and ER status was noted statistically significant (P=0.040).

Judging from the results of our study, EBV infection detected in breast cancer seems to be latent and the association of EBV to breast cancer is less likely related.