Aggressive Breast Cancer Linked to Virus

July 12, 2004 -- The rates of breast cancer vary throughout the world and now a new study links breast cancer to a virus that infects a type of house mice. The findings show that the virus may play a larger role in breast cancer in the Mediterranean and Africa than it does in the U.S.

Researchers found that 74% of Tunisian women with breast cancer tested positive for genes similar to a virus that infects mice and causes breast cancer. This compares with only about one-third of cases in people who tested positive from women in the U.S.

Viruses are known to be involved in the development of several cancers, such as leukemia and lymphoma, and several animal and large human studies show that viruses may also play a role in certain breast cancers.

Researchers say this study provides additional evidence that a human breast cancer virus exists and its prevalence varies in different regions of the world.

The results appear in the Aug. 15 issue of Cancer.

New Proof of Breast Cancer-Virus Link

Previous studies show that a virus similar to the mouse mammary tumor virus (MMTV) is associated with breast cancer. Researchers say the virus may be spread by a species of house mice that is very common in North Africa but less common in the U.S.

In the study, researchers tested 38 breast cancer tumors from women treated in Tunisia and compared the results with breast cancer tumor samples from women treated for breast cancer in other countries.

Analysis from two different laboratories showed that a significantly higher number of tumor samples from Tunisia tested positive for genes similar to the mouse breast cancer virus when compared with samples from other countries.

Nearly 75% of the breast cancer tumors from Tunisia tested positive compared with 36% of those from the U.S.; 38% from Italy; 42% from Australia; and 31% from Argentina.

Further study showed that 89% of the breast cancers that tested positive for MMTV-like genes were aggressive tumors and tended to be associated with shorter disease-free periods.