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Judging cancer news


Reports in the press have me nervous and confused about what can be done to prevent cancer. It seems that every few months a newspaper headline describes another food, activity or chemical as a risk factor for cancer. Then, all too often, another article reports on opposite result. How can we decide what to do?

Most experts in the field of cancer believe that outside factors are responsible for 70 percent to 90 percent of cancers. Identifying specific risk factors is the troublesome part, because they are almost always based on observational epidemiological studies.

In such studies, researchers examine the presence or absence of potential risk factors in people with cancer and compare them with healthy "controls." These studies can identify risk factors fairly easily when, like cigarette smoke, radiation, asbestos or exposure to sunlight, they are strongly associated with cancer. It is much more difficult for epidemiological research to pinpoint environmental factors that are weakly associated with cancer.

Epidemiologists suggest that a single study reporting a possible new cause of cancer should not be taken as "proof" unless the factor increases the risk of cancer by at least three-fold. Even then, the significance of the findings depends on the number of individuals studied, how carefully the study was performed and the biological plausibility of the results.

Unfortunately, some media tend to report the outcome of each new study as a breakthrough although the results are only weakly positive or fail to report that previous studies have failed to show the same result. The overzealous reporting often results from overly enthusiastic press releases by the institution where the research was done.

Dr. Margolis' column appears Tuesdays.

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