Can this drug prevent breast cancer?
Posted by medconsumers on June 6, 2011
The new breast cancer study was so important that the New England Journal of Medicine made the results immediately accessible on its website. A drug, long prescribed to cut the chances of recurrence in women treated for breast cancer, has shown a modest benefit to healthy women who are at high risk for developing the disease. This is the latest in the pharmaceutical industry’s decades-long search for drugs to prevent breast cancer. Unfortunately, the new study lasted only three years, so it is not known whether the drug actually prevents breast cancer or merely delays its onset. Furthermore, it remains to be seen whether the drug can reduce the risk of dying from breast cancer.
The drug in question is exemestane (brand name: Aromasin), one of class of medications known as aromatase inhibitors, which have been prescribed for years as an adjuvant treatment for women with postmenopausal, estrogen-fueled breast cancer. It is taken for several years after the initial breast cancer treatment to reduce the risk of a recurrence. The new study is the first to try it out on healthy but high-risk women. More than 4,000 postmenopausal women, median age 63 years, were randomly assigned to take either exemestane or a placebo.
At the end of the study, there were 11 invasive breast cancers in the exemestane group and 32 in the placebo group. “Most tumors in these study patients were estrogen-receptor–positive,” noted the researchers. “HER2-positive tumors, which have a poor prognosis, were also reduced with exemestane.”
Interestingly, the research team published their findings in three different statistical formats: 1) The drug-treated women had a 65% reduction in their risk of developing breast cancer; 2)In absolute terms, this boils down to 1.4% of the untreated women developed breast cancer, compared with about a half of 1% in the drug-treated women; 3) And lastly, here is what is known as “number needed to treat”: one invasive breast cancer is avoided for every 94 women taking the drug daily for three years.
When it came to adverse effects, there were “no significant differences between the two groups in terms of skeletal fractures, cardiovascular events, other cancers, or treatment-related deaths,” wrote the research team led by Paul E. Goss, MD, Massachusetts General Hospital Cancer Center. The drug-treated women showed a small increase in (or return of) menopausal symptoms such as hot flashes, fatigue, sweating, insomnia, and joint pain. This study was described as funded by “Pfizer [maker of Aromasin] and others.”
Dr. Gross was quoted yesterday in The New York Times, describing exemestane as “very safe”, which could be overly optimistic given the fact that the study lasted only three years. Not to mention another fact that the purportedly rare serious side effects like blood clots and stroke associated with other aromatase inhibitors are unlikely to show up until a far larger number of women take exemestane than the 2,000 participants in this study. Still, exemestane is already being presented as a safer alternative to tamoxifen (brand name: Nolvadex), the first anti-cancer drug proven to reduce the risk of developing breast cancer in high-risk women. (Tamoxifen never caught on for this purpose, primarily because doctors were uneasy about prescribing a cancer drug to healthy women.)
No head-to-head comparison study has been done to determine whether exemestane is actually the safer drug, but tamoxifen is far more thoroughly studied—usually against a placebo. The seven-year follow-up data on healthy but high-risk women indicate that tamoxifen has not been proven to reduce breast cancer mortality. The drug’s estimated number needed to treat is “one breast cancer is avoided after 5 years for every 95 women taking tamoxifen, and this is reduced to 56 women in those taking tamoxifen for 10 years. To see the imperfect tool for determining who is at high risk for breast cancer, click here.
While doctors and high-risk women consider the safety and effectiveness of exemestane vs tamoxifen, the first comment to the NEJM website in response to this new study came from a doctor who raised the usually ignored topic of cost: “Correct me if I’m wrong. Exemestane costs about $300/month ($3600/year). In this study 2285 patients received the drug and were treated for 3 years. 21 fewer cases of cancer were diagnosed in the treated group than the placebo– a loudly touted 65% decrease in incidence. (32 cases in the placebo group and 12 cases in the treated group) The cost/cancer prevented = 3600 X 2285 X 3/ 21 = $1,175,142 expended per cancer prevented. Is this a rational, affordable strategy in a system that is struggling with excessive costs?” Paul Goff, MD, Everson, WA.
Maryann Napoli, Center for Medical Consumers©