Research found that chemotherapy alone worked for only about 25 percent of breast cancer patients, but when they received Herceptin, too, nearly half of them improved.
"The duration of the response - how well they do and how long they stay without the disease - also significantly increased. There's a 50 percent or greater reduction of the tumor and in some cases it completely goes away," Dr. Dennis Slamon of UCLA told CBS News health correspondent Emily Senay.
About 30 percent of all women with breast cancer have the genetic mutation that Herceptin targets. The Food and Drug Administration is reviewing Herceptin and is expected to approve it within six months.
The drug offers more good news. Depending on the chemotherapy agent given, for some women, there are none of the side effects associated with the traditional chemotherapy. It doesn't cause hair loss, nausea or vomiting, or result in the suppression of the body's immune system.
So far, the side effects have been very mild, such as a little fever or sweating or chills when the drug is administered. Another side affect involves the pumping of the heart, but doctors said that also can be controlled with careful monitoring.
The gene being targeted by the drug is called HER-2. Scientists still are trying to understand why the gene mutates in some women. But Herceptin helps the body's immune system recognize specific proteins that are found on the cancer cells.