HOW TO PREVENT CANCERS

New data reported this week in the New England Journal of Medicine show a reduction in incidence of myocardial infarction and improved survival after heart attack (Yeh, et al). This population based study from Kaiser Permanente in Northern California highlights the relatively rapid effect that improvements in the managing of risk factors can have on cardiovascular disease. From 1999 to 2008 the proportion of patients with high blood pressure who were successfully treated to meet target levels increased from 40 percent to 80 percent. And the proportion meeting targets for blood cholesterol also increased.

The 24 percent decrease in myocardial infarction seen in this population in just ten years highlights just how important time frame is for prevention. Cardiovascular risk factors respond to interventions relatively quickly, and subsequently, the risk of heart attack drops quickly. Taking aspirin lowers the risk of heart attack within hours. Stopping smoking lowers risk significantly over the first year of quitting. Improvements in blood pressure have a similar effect.

In contrast, there’s cancer risk, where we do not have this ready range of intermediate markers that are either amenable to preventive interventions or show rapid responses. Some factors have relatively quick impacts on cancer risk – tamoxifen and raloxifene lower breast cancer risk within 1 – 2 years; smoking cessation lowers lung cancer risk by half within five years. And removal of colon polyps found by screening significantly lowers later risk of cancer. Yet, none of these is the hard and fast marker that high blood pressure or similar measures are for cardiovascular disease. And even though we know that estrogen levels in postmenopausal women are a very good marker of breast cancer risk – similar in magnitude to the link between unhealthy cholesterol levels and heart disease - we don’t currently use it as such.

For cancer, the long lag between lifetime exposure to a risk factor and cancer onset leads to many challenges in documenting the benefits of prevention. We know that high levels of activity reduce risk of breast and colon cancer and that obesity increases the risk of many cancers. How quickly risk responds to changes in these components of our modern lifestyle, though, is not clear. For smoking, the measurement of exposure is somewhat easier, and the event of stopping smoking is clearly marked in the minds of most smokers. This helps us document the benefits of quitting for cancer (Kenfield, et al; CNiC Prevention Spotlight). Most cancer risk factors, though, don’t have such a clear cut beginning (or end) or have such a quick effect on risk, which makes assessing the specific timeline of cancer prevention difficult.

Despite such uncertainties, the balance of evidence shows that cancer is largely preventable and that many of the same lifestyle changes that boost heart health also lower cancer risk. The benefits may take longer to come around than for heart disease, but in the end they’ll be no less real and no less important.