Common virus seen in breast tumors.

Epstein-Barr virus (EBV), the common herpes virus that causes infectious mononucleosis, appears in breast tumors with unusual frequency, a new study finds.

Research has linked EBV with several other cancers, such as Hodgkin's disease, B-cell lymphoma, Burkitt's lymphoma, and stomach cancer. While its presence in some breast cancer patients also emerged in two earlier studies, the new results show a stronger link and suggest that EBV is most likely to appear in the breast cancers that carry the poorest prognosis.

Scientists examined tumor tissue from 100 randomly selected breast cancer patients. The virus appeared in 51 of the tissue samples. In contrast, analysis of 30 samples collected from healthy breast tissue from the breast cancer patients showed that only 3 contained EBV, says Irene Joab, a biochemist at Saint Louis Hospital in Paris. The report appears in the Aug. 18 JOURNAL OF THE NATIONAL CANCER INSTITUTE (JNCI).

The two previous studies reported EBV in 21 percent and 41 percent of breast tumors. The new study not only showed a higher rate, 51 percent, but also revealed a tendency for the virus to crop up more often in aggressive cancers. For example, EBV was present in 18 of 25 cancers (72 percent) in which cancer had spread to more than three lymph nodes. In contrast, the virus appeared in only 33 of 75 patients (44 percent) with cancer in three or fewer lymph nodes.

EBV was less common in tumor cells showing certain hormone-receptor molecules than in cells lacking these receptors, Joab says. The latter cancers have a poor prognosis.

Ian Magrath and Kishor Bhatia of the National Cancer Institute in Bethesda, Md., caution that several other studies have found no link between EBV and breast cancer. However, these earlier studies employed less thorough tests for EBV, they note. "Although more data are needed, it seems likely at this time the EBV is frequently associated with multiple ... types of breast cancer," they say in the same issue of JNCI.

The question remains as to whether EBV directly causes breast cancer. Magrath and Bhatia suggest the virus might be attracted to preexisting cancer cells and infect them preferentially. However, Joab and her colleagues note that the virus' presence in some cancerous lymph nodes suggests that the virus had infected breast cells before the tumor spread.

In either case, EBV could play a role in breast cancer diagnosis, Magrath and Bhatia say.