Lycopene, tomato products and prostate cancer incidence: A review and reassessment in the PSA screening era

Lycopene has been proposed to protect against prostate cancer through various properties including decreased lipid oxidation, inhibition of cancer cell proliferation, and most notably potent antioxidant properties. Randomized interventions of lycopene and prostate cancer risk have been limited in scope, and thus do not provide strong support either for or against a causal association. The epidemiologic literature on lycopene intake or serum level and prostate cancer based on observational studies has been mixed. Detection of an association has been complicated by unique epidemiologic considerations including the measurement of lycopene and its major source in the diet, tomato products, and prostate cancer incidence and progression. Studies based on intake are limited by the assessment of intake, food composition databases, and differences in bioavailability. Prospective studies are preferable to avoid various biases, such as recall bias, or reverse causation in studies of circulating lycopene. Understanding this association has been further challenging in the prostate specific antigen (PSA) screening era. PSA screening has increased the detection of prostate cancer, including a variety of relatively indolent cancers. This review examines the lycopene and prostate cancer association in light of epidemiologic methodologic issues with particular emphasis on the effect of PSA screening on this association. With increasing use of PSA, it is becoming increasingly difficult to examine advanced stage prostate cancer, at least in some populations. Examining potential mediators or markers of aggressive behavior in tumor tissue may be another useful approach in the further study of lycopene and prostate cancer risk.