ASCO, the annual conference for the American Society of Clinical Oncology, has just ended, and with it the attendant media circus. More than 20,000 oncologists from around the world attend the event, participating in the hundreds of conferences and educational seminars, and perusing the thousands of scientific presentations. It is a time to learn, to update, to network, to share ideas. It is also a time for NBC, and CNN, the newspapers, and the other major media outlets to report on all the latest findings in cancer research and treatment. Unfortunately, in the rush for headlines and attention there is a tendency to overplay the reporting. Serious science is discussed at the conference, and important developments in the treatment of cancer are reported, but these are typically small steps forward, not the “major breakthroughs” that the headlines would lead us to believe. As a result, during the week of the convention oncologists across the country are fielding phone calls from their patients telling them that yes, there is progress, but no, what you just heard on TV is not going to significantly change how we treat your cancer.
As an example, on the TV news last weekend one caption read “new pill prevents breast cancer”. Dealing with the same subject, a headline on the CBS website rather breathlessly reports “breast cancer risk slashed by hormone-blocking pill.”
Lets look at what was really reported. This particular story deals with a trial reported at the ASCO convention, and published online in the New England Journal of Medicine. The trial studied the use of the drug exemestane (Aromasin) to prevent breast cancer in women deemed at high risk of the disease.
Some key points:
- The study was limited to women who were postmenopausal
- Women in the study did not have a history of invasive breast cancer. They were considered to be at high risk of developing breast cancer, either because of age, high score on the Gail model, or previous abnormal biopsies.
- Exemestane is an aromatase inhibitor. In post-menopausal women it blocks the formation of estrogen in the body. Aromatase inhibitors do not work for pre-menopausal women, as it does not block estrogen synthesis in the ovaries.
- The drug Tamoxifen, which blocks estrogen receptors (rather that interfering with estrogen synthesis) had already been shown to decrease cancer incidence in an NSABP study published in 1998. In this study Tamoxifen reduced the risk of invasive (and non invasive) breast cancers by 50%. There were 22 cancers per 1000 women taking Tamoxifen, and 43 cancers per 1000 women taking placebo.
- Tamoxifen does have side effects, including the possibility of developing blood clots and cancer of the uterus.
- While is was reasonable to assume that aromatase inhibitors would help prevent breast cancer just as Tamoxifen does, this had not previously been shown in a clinical trial. This new trial demonstrates that it does indeed help.
The question is, how big a difference does the drug make? By how much does it decrease the risk of developing breast cancer or, to put it a different way, how many cancers does it prevent?
In the exemestane trial:
- A total of 4560 patients were enrolled. 2285 received exemestane, 2275 received placebo.
- After 3 years, invasive breast cancer was detected in 11 patients taking exemestane, and in 33 patients on placebo
- That translates into 4.8 cancers per 1000 patients on exemestane, contrasted with 14 cancers per 1000 patients on placebo.
- Put another way, over the three years breast cancer occurred in 0.5% of women on exemestane, and in 1.5% of women on placebo.
- The drug also prevented precancerous lesions such as DCIS and atypical ductal and lobular hyperplasia. This, and longer follow-up, may ultimately result in even more impressive results than those currently reported.
- There were no differences in the number or type of adverse effects between exemestane and placebo, nor were there differences in quality of life.
What conclusions can be drawn from this information? First, we can say that anti-estrogen therapy with an aromatase inhibiter such as exemestane can, like Tamoxifen, decrease the risk of breast cancer. This is a good thing. However, the study was not designed to show that such risk reduction results in longer life. Presumably patients deemed to be a higher risk have close follow up, and if a tumor does occur it may be found early and treated. Still, prevention is better than treatment.
Second, while the drug does prevent breast cancer, the percentages are small. To say as CBS does that breast-cancer risk is “slashed” is just a bit of an exaggeration. However, we also need to keep in mind that small improvements in a fairly common disease can translate into large absolute numbers of patients helped.
Finally, which patients should be taking these drugs? Those enrolled in the trail were considered to be at risk based on the criteria outlined above, and patients can use them as a starting point for a discussion with their personal physicians.
