Commentary

How many women must be treated to avert one case?


 

References

THE CASE FOR CHEMOPREVENTION AS A TOOL TO AVERT BREAST CANCER STEVEN R. GOLDSTEIN, MD (JULY).

In his article about chemoprevention of breast cancer, Dr. Goldstein provided relative-risk tables. I think it would also be helpful to see “need to treat” statistics. That is, how many patients need to take one of these medications to prevent one case of breast cancer? This information is never stated, and I think it is very important information to have if you are a woman trying to decide whether to take one of these expensive drugs.

Donald R. Joyner, MD
Great Falls, Mont

Dr. Goldstein responds: The number needed to treat can be high

In the Multiple Outcomes of Raloxifene Evaluation, or MORE trial, which evaluated women who had osteoporosis rather than a high risk of invasive breast cancer, the absolute risk reduction for invasive breast cancer was 3.1 fewer cases for every 1,000 woman-years of raloxifene use.1 The number needed to treat (NNT) to prevent one case of cancer: 323 women for 1 year.2

In the Study of Tamoxifen and Raloxifene (STAR), which evaluated women at high risk of invasive breast cancer, there was no placebo group, and the incidence of invasive breast cancer was similar between the tamoxifen and raloxifene groups.3

In the P-1 trial, which compared tamoxifen with placebo, there were 178 cases of invasive breast cancer in the placebo group versus 89 cases in the tamoxifen group (relative risk reduction, 51%).4 The rate of invasive breast cancer was 6.76 cases for every 1,000 women in the placebo group, compared with 3.43 cases for every 1,000 women in the tamoxifen group. The absolute risk reduction was 3.33%, and the NNT was 300 women for 1 year.4

It is useful to compare these figures with data from another area of treatment, such as the use of atorvastatin (Lipitor) to reduce coronary artery disease (CAD). In a trial of men who were at high risk of CAD (i.e., hypertensive patients who had at least three risk factors), the package insert states that Lipitor significantly reduced the rate of fatal CAD (46 events in the placebo group versus 40 events in the Lipitor group) and nonfatal myocardial infarction (108 events in the placebo group versus 60 events in the Lipitor group), with a relative risk reduction of 36% (P=.0005) (based on an incidence of 1.9% for Lipitor versus 3.0% for placebo). This translates to an absolute risk reduction of 1.1%. One needs to treat 90 such patients for 1 year to prevent the first major CAD event.

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