Cancer Prevention: Better Late than Never?

The historical view of cancer etiology has been that the latent period between a carcinogenic exposure and the diagnosis of this disease is typically quite long. This impression has been fueled by numerous epidemiologic studies, including those of occupational cancer (for example, one review reported a 35-year mean difference between asbestos exposure and mesothelioma [1]), radiogenic cancer (another study indicated that excess cases of cancer were still occurring in Japanese survivors of the atomic bomb 40 years later [2]), and early-life risk factors for breast cancer (most studies have found that ages at menarche and first live birth were risk factors [3]).

This perspective was further supported by results from bioassays of carcinogens in a study of laboratory animals. In a review [4], inverse relations between dose and duration of the latent period were frequently noted; even high-dose exposures were often associated with latency periods that involved a considerable percentage of the animal's expected life span. As a result of these observations and other studies, clinicians and the general public developed a certain sense that cancer prevention efforts for middle-aged and elderly persons (in whom the disease takes its greatest toll) were futile.

In the research community, this view has shifted incrementally and, ultimately, radically during the past 25 years on the basis of accumulating epidemiologic and laboratory evidence. Early in this period, excess risks for lymphoma related to immunosuppressive drug use [5] and risks for endometrial cancer related to hormone replacement therapy [6] were noted to appear shortly after initiation of treatment …