Screening and epidemiology

Epidemiology is the study of how disease presents in populations. In epidemiologic studies, factors that influence the risk of getting a disease and the survival from the disease at a population level are examined. Screening attempts to discover disease prior to the development of clinical symptoms. Screening for prostate cancer remains controversial. Prostate cancer is highly prevalent and the incidence increases with age. Nevertheless, mortality from this disease is very low and mortality rates have been decreasing in the last two decades. Retrospective reports addressing the impact of screening in prostate cancer are conflicting with some studies concluding that there is no benefit in improved cancer specific mortality, while others demonstrating a marginal benefit. The two recent randomized trials addressing the question of screening demonstrates that screening improves the detection of earlier stages of cancer at a significant cost of overdiagnosis and overtreatment. Finding markers of aggressive disease applicable to biopsy specimens would help decrease overtreatment of prostate cancer by more appropriately selecting patients with more aggressive tumors that would impact mortality for treatment versus observation. The search for modifiable features of diet, physical activity, and environmental exposures continues to provide possible sources of primary prevention. Evidence is emerging that prostate cancer risk may be related to exposures to inflammation and infection, including possible retroviral infections. In this chapter, we will provide a broad overview of prostate cancer screening including the controversies about and limitations of screening. We will conclude with a review of the epidemiological evidence for primary prevention strategies in prostate cancer, and review why many of these strategies fail in randomized trial settings.