Background: It has been postulated that inflammation caused by certain viruses might result in cancer. Recently, it was shown that childhood lymphoblastic leukemia, breast and ovarian cancers express an interferon-related signature, providing support for this notion. We have previously shown that 38% of the sporadic breast cancers contain MMTV-like env gene sequences. To find out if the presence and expression of MMTV-like sequences correlated with an inflammatory phenotype, we have compared the expression profile of two sublines of MCF-7 cells, one containing the MMTV-like sequences (env+), the other one lacking them (env-). Results: The results indicated that there were 47 differentially expressed genes between the two sublines. Among 27 upregulated genes in the env+ cells there were 7 interferon-related genes, 5 TNF-connected genes and 2 TGFβ-related genes. Conclusion: These results suggest that the env+ cells were most likely responding to an infectious agent, and support the hypothesis that a viral infection may play a role in breast cancer pathogenesis.