Scientists have discovered a new gene that is believed to be a major cause of breast cancer among women. Between 30 and 40 percent of women with breast cancer have a malfunctioning version of the IKBKE gene, which scientists believe can cause breast cancer due to harmful mutations.

The study is being hailed as a way for drug companies to target breast cancer effectively and a new innovation in helping scientists scan tumors for genetic mutations.

IKBKE is present in immune cells and helps the body fight viruses. It has no function in breast cells, and if it is triggered, it can easily cause cells to malfunction and proliferate.

During the study, researchers "switched off" the gene by interfering with its functioning. When it was rendered inactive, the cancerous cells began to die out.

In an interview with "Science News," doctors expressed optimism that the discovery could be a breakthrough for fighting breast cancer.

"I actually think [the new study] is a pretty big deal," says Gordon Mills of the M.D. Anderson Cancer Center in Houston. "I doubt that there are many more [breast cancer] genes of this magnitude to be found."

Breast cancer is the second most common form of cancer among women (after skin cancer). According to the American Cancer Society, an estimated 40,000 women died of breast cancer in the United States in 2001.