The discovery of an enzyme linked to breast cancer's deadly spread may open new treatment avenues against the disease that kills nearly 45,000 American women annually, scientists reported this week.

A French research team said it has identified an enzyme produced by the tissue around invasive breast tumors that is not present near tumors confined to a single, small area.The enzyme, called stromelysin-3, belongs to a family of proteins that destroy the connective tissue surrounding cells during growth of an embryo. The new enzyme appears to "eat through" a breast tumor's connective tissue, allowing cancer cells to spread beyond the original tumor site and enabling blood vessels to feed tumor growth, said Pierre Chambon, who directed the study.

In addition to detecting stromelysin-3, Chambon and his colleagues from INSERM's biochemistry institute in France also pinpointed the gene that carries instructions for the production of the enzyme.

"It is the first gene that has been identified that seems to be clearly related to (breast tumor) invasion, and invasion is very important. Usually, a patient doesn't die from a contained tumor - a patient dies from invasion," Chambon said in a telephone interview.

About 20 percent to 30 percent of breast tumors detected by mammography are not invasive, while almost all breast tumors found by manual exams are invasive, said Dr. William McGuire, head of medical oncology at the University of Texas Health Science Center in San Antonio. If caught in a non-invasive state, breast cancer is almost 100 percent curable, he added.

Chambon said the new findings open "a potentially new avenue for therapy" against breast cancer.

One strategy would be to develop a small molecule, perhaps a tiny piece of protein patterned after those that naturally inhibit related enzymes, to block stromelysin-3 large.