Tuesday, July 20, 2010

Screening, early detection, and risk reduction

While awareness continues to grow that screening for breast cancer, like other screening tests, aims to detect cancer earlier, when it is more successfully treated, it is clear that screening tests are not perfect and those who test positive require additional follow-up to confirm the diagnosis and chose an appropriate therapy. Equally important, but less often the focus of visits to health care providers, is the potential to prevent or reduce the chance of ever developing cancer. We have discussed some of the breast cancer prevention strategies in recent posts, such as drugs, and weight loss. But you might ask, how do we know what level of risk for cancer we actually have? While a growing number of tools are available on web sites for “risk estimation” lets consider some of the “behind the screen” realities here.

Risk
Risk is a person's chance of getting a disease over a certain period of time. There are many different ways to present risk. In addition to age, a number of genetic factors (summarized most readily in family history of the disease) as well as lifestyle (including smoking, weight gain, physical activity, diet, alcohol) and infections may contribute to risk. Summing up the contribution of these factors in addition to age, one can estimate the risk of developing a specific disease in a given number of years (say 5-year risk) or over a lifetime. Of course, this risk is only an estimate. It can be presented as a numeric value or as a word classifying the level of risk compared to the average risk for someone of the same age. Calculating an individual's risk of disease is an inexact science. In the end, one either gets the disease or remains free from it, but at the outset risk of future disease falls along a gradient.  In Your Disease Risk, we estimate your risk of ever developing a disease in your lifetime compared to an average person who's your same age and sex.

In addition to focusing on the actual number or word classification for the level of risk, we believe that risk estimation can be helpful to classify level of risk. With this information one can then identify steps to take to reduce risk. The higher one is above the average for your age, the more things one might consider doing or at some level one takes drugs (e.g., cholesterol lowering drugs) to reduce the risk. Even with this reduction in cholesterol, risk is not removed to zero – every year some patients taking cholesterol lowering drugs still have heart attacks. Likewise for blood pressure medications. That said, these risk reduction strategies each prevent many thousands of cases of heart disease and stroke each year. As we recently noted (see post), heart disease continues to decline in populations that adhere to risk reduction strategies.

For Heart disease, the data from the Framingham Heart Study were taken to develop the risk prediction model that has been widely used in practice to guide prevention strategies that primarily focus on blood pressure and cholesterol. To this we add the lifestyle factors that other population studies, many modeled on the Framingham Heart Study, have shown are also related to heart disease risk.  For breast cancer we include a broad range of factors and can build substantial differences in risk between the top categories and the bottom. Likewise for colon cancer we have almost 10-fold differences in risk between the those in the highest category of risk and those in the lowest risk group, with healthiest lifestyle.

Risk reduction
As with any screening test, there should be a follow-on from the estimation or assessment of risk. Just as it is unethical to screen for a disease that does not have effective therapy, so it is likewise unethical and misleading to estimate risk and not also have available to those who get the risk estimate a summary of ways things they may do to lower their risk. Following this approach when we estimate risk at our web site, we highlight steps you can take to lower your risk.

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