Drug to treat breast cancer may help prevent it

Doctors and patients may have a new way to prevent breast cancer -- a drug that's already approved to keep it from reappearing in women who've had it.

According to a new study, the hormone-blocking drug Aromasin reduced the risk of invasive breast cancer by 65 percent in post-menopausal women at high risk for breast cancer. Aromasin also has fewer side effects than other drugs approved to prevent the disease.

The study, announced Saturday at the annual meeting of the American Society of Clinical Oncology and published online by the New England Journal of Medicine, "really signifies the paradigm shift," CBS News Medical Correspondent Dr. Jennifer Ashton told "Early Show" co-anchor Chris Wragge Monday. "We've gotten very good at treating breast cancer. Now, the bent of the research is focused on prevention."

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Researchers enrolled 4,560 healthy, postmenopausal women at high risk for breast cancer in a placebo-controlled clinical trial.

A 65 percent risk reduction was found after women had been taking the drugs for only three years. In absolute terms, 94 women would have to be treated for 3 years to prevent one case of breast cancer.

Aromasin is in a class of drugs called Aromatase inhibitors, which are currently being used to prevent recurrence of breast cancer in women recovering from the disease.

Many studies have shown that estrogen produced by the body promotes breast tumors. Aromasin is one of three Aromatase inhibitors that block the production of estrogen in post-menopausal women.

"Of all of the women battling breast cancer," Ashton says, "about two-thirds of them have a form of the disease we refer to as being hormonally sensitive. Basically, this drug works as an anti-estrogen."

The study was, Ashton observed, "very reputable" and appears in "the best medical journal we have," but she also pointed out that it "was funded (in part) by the drug maker (Pfizer), although they did not have a direct role in how the data was collected or in the study design."

What constitutes a woman being at high risk for breast cancer?

"In this study and in general," Ashton added, "when you talk about high risk for breast cancer, age is the number one factor. Over the age of 60 were the women in this study. Post menopausal women. Other things that make you high-risk: your family history, or if you've had another type of breast cancer in the past."

Aromatase isn't the first drug approved to prevent breast cancer. Tamoxifen and Raloxifene are also used for that purpose, but can have serious side effects, such as blood clots and uterine cancer.

Aromasin doesn't appear to have those side effects and might be more tolerable, but its side effects can still be, Ashton told Wragge, "pretty troubling. They can be hot flashes, fatigue, joint pain.

"In fact, women on this class of medication have a high discontinuation rate of stopping those medications when they already have breast cancer, so it remains to be seen whether women who don't yet have breast cancer will be able to stick with (the drug, considering) those side effects."

Another thing that concerns researchers is that the long-term impact of taking Aromasin isn't known.

It's important, Ashton stresses, that women talk to their doctor to fully understand the risks and benefits of taking these drugs to prevent getting breast cancer.