Newswise — The debate about whether or not lycopene or some other phytochemicals from tomatoes might reduce prostate cancer risk is apparently not over. Dr Edward Giovannucci from Harvard Medical School published an editorial in the July 2007 issue of the Journal of the National Cancer Institute that responded to a report in the same issue from the FDA that stated that a “very low level of comfort” existed with tomato and tomato product consumption decreasing the risk of prostate cancer.

The essence of Dr. Giovannucci’s argument that this conclusion may be flawed is that studies on lycopenes, tomatoes, and prostate cancer risk are influenced by PSA screening. He focused on how PSA screening influences the diagnosis and epidemiology of CaP and when during prostate carcinogenesis this is a factor. Prior to PSA most CaP patients had advanced cancers at diagnosis. However, in the PSA era, many diagnosed prostate cancers are low risk and indolent and likely would not have been detected in the pre-PSA era. In the absence of PSA screening, the diagnosis of carcinoma of the prostate follows a period of tumor proliferation that was stimulated by an internal or external factor. However, in the PSA era he argues, the diagnosis of CaP often signifies that a man just happened to have a PSA test.

He used the data from the Health Professionals Follow-up Study (HPFS), a cohort evaluated for risk factors and cancer. The HPFS reported that risk factors associated with an increased risk of CaP mortality were a higher incidence of CaP, an increased likelihood of poor prostate tumor differentiation, a preferential increase in the progression of highly differentiated tumors, or an increase CaP death rate independent of incidence stage at diagnosis or grade. In the HPFS, dietary factors associated with increased CaP mortality were not associated with an increase in incidence but rather increased tumor progression or an increase in the fatality rate. Thus, he states that studies not supporting an association between CaP lycopene, tomatoes, and CaP incident rates may reflect the impact of PSA screening. Earlier studies performed in the pre-PSA era did show an association. The evidence associating tomatoes or lycopene and tumor progression are stronger for more advanced-stage cancers, which may be difficult to show in PSA screened cancers. Furthermore, the HPFS straddled the pre-PSA and PSA era and from 1986-1992 there was an inverse association between tomato intake and total CaP incidence stronger for advanced-stage disease. During 1992-1998 the association was weak but a strong inverse association persisted for metastatic CaP. An analysis from 1992-2002 found no statistical association.

Dr. Giovannucci states that the relationship between prostate cancer risk and tomato and lycopene dietary intake is complex and the European Prospective Investigation into Cancer and Nutrition Study may help to better answer this question. J Nat Cancer Institute. 99(14):1060-2, July 2007 doi:10.1093/jnci/djm048


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