Interpreting the Data From PLCO

Numerous studies over the years have demonstrated that the antioxidant lycopene can play a role in preventing or delaying the progression of prostate cancer. Yet recently released data from the PLCO (Prostate, Lung, Colorectal, Ovarian) Trial suggest that the benefit of lycopene is small.

Drs. Peter Gann and Edward Giovannucci, authors of the PCF’s Nutrition and Prostate Cancer guide offer some insight into how to interpret the latest results in light of the long-term data already accumulated.

The current report from the PLCO Trial measured lycopene levels in the blood of 692 men who eventually developed prostate cancer and 844 matched controls.  These men were among the 38,000 enrolled in the prostate cancer screening substudy of the PLCO.  The new analysis found no connection between increased levels of lycopene and a reduced risk of developing prostate cancer.

By contrast, data from the Health Professionals Follow-Up Study (HPFS) and the Physicians' Health Study (PHS) demonstrated that lycopene consumed at a steady rate over many years can prevent prostate tumors from progressing to more advanced stages.

The latest findings from PLCO do not negate the data from HPFS or PHS. Rather, they confirm the findings from HPFS and PHS that the benefits of lycopene are not seen over the short term and are seen in men with more aggressive disease that is likely to progress.

Because the goal of PLCO is to determine whether the use of screening tests can reduce mortality from cancer, the men enrolled in the study underwent regular PSA and DRE tests to detect prostate cancer. Although this method ensured that the cancers would be detected in their earliest stages, it also greatly decreased the likelihood that aggressive cancers would grow unchecked and be allowed to progress. As only 13% of patients had aggressive disease, it is probably unlikely that the benefits of lycopene in slowing disease progression would be seen in PLCO.

About the Studies
The Health Professionals Follow-Up Study, begun in 1986, was designed to look at the effects of various nutritional and lifestyle factors on the development of cancer, cardiovascular diseases, and other serious illnesses affecting men. Every two to four years, over 50,000 men enrolled in this ongoing study complete questionnaires about their health, their smoking status, their level of physical activity, and their diet and nutritional status.

The Physicians' Health Study was a randomized controlled trial begun in 1982 to evaluate the effects of aspirin and beta-carotene on the prevention of cardiovascular disease and cancer. Although that trial technically ended in 1995, a large percentage of the 22,000 male physicians who took part in it continue to complete questionnaires about their health, effectively turning the trial into a long-term epidemiologic study. However, unlike the Health Professionals Follow-Up Study, the Physicians' Health Study focuses more on biomarkers for disease, exploring the link between specific compounds found in the bloodstream and the risk of developing disease.

More than 7000 of the participants in the original Physicians' Health Study plus an additional 7000 men were enrolled in a second trial begun in 1997, examining the effects of vitamin C, vitamin E, beta-carotene, and a multivitamin on the prevention of cardiovascular disease, cancer, age-related eye disease, and early cognitive decline.

The Prostate, Lung, Colorectal and Ovarian Cancer Screening (PLCO) Trial is a large-scale clinical trial to determine whether certain cancer screening tests reduce deaths from these cancers. The PLCO Trial also includes research on the genetic and environmental causes of cancer and studies of new methods for the early detection of cancer.

The primary objective of the prostate component of the PLCO trial is to determine, in men age 55 to 74 years old at entry, whether screening with DRE plus serum PSA can decrease mortality from prostate cancer. The 38,000 men enrolled underwent PSA testing and DRE upon entry. The men then have these tests annually for the next three years, and then have a PSA test without DRE in years 4 and 5. Participants in the intervention and control groups are contacted yearly for 13 years from the time they enter the study in order for the researchers to monitor their health.