Reported by Tiffany Chao, M.D.

CHICAGO - A new form of breast cancer treatment may be… smallpox?

What was once a feared killer of millions of people may someday be used to treat one of the most dangerous forms of breast cancer. So far it's worked in mice, and researchers are encouraged.

The researchers, from Memorial Sloan-Kettering Cancer Center in New York City, have found that a virus from the smallpox family can be used in the treatment of a certain type of breast cancer, called triple-negative breast cancer or TNBC.

This form of breast cancer is especially difficult to treat because it is not sensitive to the special hormonal and immune therapies that many other forms of breast cancer are. These tumors can be often be treated with some chemotherapy, but they tend to be more aggressive and recur more often.

"One of the reasons I wanted to focus on TNBC is that there aren't many long-term treatment options," said Dr. Sepideh Gholami, the lead study author and a surgical resident at Stanford University Medical Center. "Right now the only options are surgery and chemotherapy, but these cancers metastasize early on and are really aggressive. Resistance develops fast to multiple agents of chemotherapy so patients run out of options easily."

It is estimated that about 10 to 20 percent of all breast cancer cases are triple-negative. It is particularly prevalent in women under the age of 35.

Study findings presented today at the 2012 Annual Clinical Congress of the American College of Surgeons showed that the vaccinia virus, called GLV-1h164, was able to enter cells and cause destruction of the tumor, as well as prevent blood vessel growth in the tumors in mouse animal models, resulting in significant tumor destruction.

Since smallpox vaccines have been given to billions of people to eradicate smallpox, this new vaccine will likely have a similar level of safety. However, its use as a therapy in patients with triple negative breast cancer would require a clinical trial to evaluate its effectiveness.