Prostate cancer screening and the PLCO trial

Between 1993 (when it was started) and 2001 (when it was closed to enrollment), the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer trial enrolled nearly 155,000 men and women of 55 to 74 years of age. Half of them (the “intervention” arm) underwent regular cancer testing; the other half (the “control” arm) just carried on with their normal health care routine.

One of the primary goals of this trial was to determine whether regular testing (“screening’) for prostate cancer with a digital rectal exam (DRE) and a prostate specific antigen (PSA) test leads to a reduction in deaths from prostate cancer. A total of 38,350 men are enrolled in the prostate cancer intervention arm. Other similar goals address the other three cancers under study.

The active testing element of the study was completed in 2006. Additional follow up was originally expected to continue until 2014 to determine the benefits (or harms) of the screening processes that are being studied. Thus, we did not expect to see the results of this study until perhaps 2015.

However, in early 2009, a major report giving the results of this study at 7 to 10 years of follow-up was unexpectedly published in the New England Journal of Medicine. The results caused the expected controversy.

In reporting the results of this trial, Andriole et al. state that this study enrolled 76,693 men at 10 study centers in the USA into its prostate cancer component. These men were randomly assigned to one or other of two groups: an annual screening group of 38,343 men and a “usual care” group of 38,350 control patients.

The men in the annual screening group were offered a PSA test every year for 6 years and a physical examination (a DRE) every year for 4 years. All PSA tests were performed at a single laboratory. The men in the screening group and their health care providers were given the results of these tests and decided together on any necessary follow-up evaluations. It is very important to understand that men in the “usual care” group also received PSA and DRE tests according to the recommendations of certain professional organizations. The distinction is that these men were not being rigorously tested according to the specific protocol used for the screening group.

All patients were followed  for 7 to 10 years and all cancers, deaths, and causes of death were identified and recorded.

The results of this US-based trial are as follows:

  • There was an 86 percent compliance rate for annual PSA testing in the screening group, and an 86 percent compliance with DRE testing.
  • Rates of PSA testing in the usual care group ranged from 40 percent in the first year to 52 percent in the sixth year and for DRE testing in these men they ranged from 41 percent in the first year to 46 percent in the fourth year; in other words, approximately half of the men in the control group were being regularly tested for risk of prostate cancer!
  • At 7 years of follow-up, the incidence of prostate cancer in the screening group was 116/10,000  person-years (for a total of 2,820 cancers diagnosed) and the incidence of prostate cancer in the control group was 95/10,000 person-years (for a total of 2,322 cancers diagnosed).
  • The incidence of prostate cancer-specific death was 2.0/10,000 person-years (50 deaths) in the screening group and 1.7/10,000 person-years (44 deaths) in the control group.

The authors of the study conclude only that, “After 7 to 10 years of follow-up, the rate of death from prostate cancer was very low and did not differ significantly between the two study groups.”

Now we cannot conclude much more from this study than what the authors stated above. We have to remember that this study was originally designed to run for a further 5 years, until 2014, before the results were presented. For whatever reason, it was decided to publish the interim results of this study earlier — but the trial is continuing, and may find that by 2015 there is a significant survival benefit. However, given the data presented above, The “New” Prostate Cancer InfoLink suspects that even if there is a statistically significant survival by that time, it may still not be clinically meaningful.

In a separate publication, the lead author of the PLCO study, Dr. Gerald Andriole, made a number of additional comments expressing his personal opinions of what this study implied. Here is what he said:

  • “… for men with a life expectancy of 7 to 10 years or less, it is probably not necessary to be screened for prostate cancer.”
  • “So far, only a minority of men enrolled in the PLCO study have died, so it may be premature to make generalizations about the ultimate results of the trial.”
  • “We don’t have enough data yet about the youngest men in the study — those in their 50s — and it may be that over time, we will, in fact, see a benefit from screening.”
  • “We definitely need to find better ways to detect and treat aggressive tumors, those that are truly life-threatening, so that men with slow-growing tumors can avoid unnecessary treatments.”
  • “My recommendation is that, for now, men with a life expectancy of more than 7 to 10 years continue to be screened for prostate cancer.”
Content on this page last reviewed and updated May 4, 2009.
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