The results of a massive clinical trial for the prevention of breast cancer, released on Apr. 17, contained mostly good news for women, though there were a number of caveats. Evista, a drug from Eli Lilly & Co. (LLY) that's already widely used to treat osteoporosis, proved just as effective at preventing invasive breast cancer in older, high-risk women as the current gold standard, tamoxifen, but with fewer serious side effects. Tamoxifen, a 30-year old drug that mimics estrogen, cuts the risk of developing breast cancer in half for post-menopausal women. But it also increases the risk of such rare but serious side effects as blood clots and uterine cancer.
The study of Evista by the National Cancer Institute, part of the government's National Institutes of Health (NIH), was one of the largest and longest-running trials ever conducted. Called the STAR trial, it covered 19,797 women and ran for five years. It found that Evista, a close chemical cousin of Tamoxifen, reduced the risk of invasive breast cancer by half, roughly the same as tamoxifen. But women on Evista had 29% fewer blood clots and 36% fewer cases of uterine cancer than those on the older drug. They also had a lower risk of developing cataracts.
Evista, however, didn't provide improved results for all women. It wasn't as effective as tamoxifen in lowering the risk of two non-invasive forms of breast cancer: ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). These types of cancer are rarely deadly, but they can turn into more dangerous forms of the disease.
"As a result, the outcome of the study isn't as clear cut as we might have hoped for," says Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. "It will take some time for experts to review the data to determine which of the two treatments is preferable."
Nevertheless, the results were trumpeted by the STAR researchers -- and by Lilly. For the company, STAR made up for the last week's disappointing finding that Evista doesn't reduce the risk of heart attacks, as Lilly had hoped. Lilly says it will now seek Food & Drug Administration approval of the drug for the prevention of invasive breast cancer. Because the drug is already on the market for the treatment of osteoporosis and the condition it treats is so serious, that approval could come as soon as this summer.
Evista is currently taken by some 500,000 women in the U.S. to prevent osteoporosis, a bone-wasting disease common in post-menopausal women. It's Lilly's fourth best-selling drug, and pulled in more than $1 billion in sales in 2005. Tamoxifen is currently marketed by Astra Zeneca (AZN) as Nolvadex. However, the company has said it plans to phase out the drug by the end of June, since there are numerous generic versions. The FDA has approved several companies to make the generics, including Barr Pharmaceuticals (BRL) and Teva Pharmaceutical Industries (TEVA).
The STAR trial results were heralded by cancer experts, as it proves the principle that drugs can not only treat cancer but actually prevent it. Such so-called chemoprevention is an area of growing focus in oncology, as researchers seek ways to outwit the disease. Cancer continues to kill half its victims despite hundreds of millions of dollars that have been poured into finding new treatments, so there's a growing interest in trying to prevent tumors from ever gaining a foothold in the first place.
Women who participated in the STAR trial were at least 35 years old, post-menopausal, and had an increased risk of breast cancer, based on their age and their personal and family medical histories. The researchers who ran the trial said women who are on Tamoxifen should consult with their doctors before deciding to switch to Evista.