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Re-analysis of data from the PCLO screening study — what is truth?

Posted Nov 02 2010 12:00am

A re-analysis of data from the prostate cancer screening arm of the Prostate, Lung, Colon, and Ovarian  (PLCO) cancer screening study has now stated that, “Selective use of PSA screening for men in good health appears to reduce the risk of [prostate cancer-specific mortality] with minimal overtreatment.”

The 76,693 men who participated in this study between 1993 and 2001, did a lot more than just turn up occasionally at one of 10 centers for screening tests. For example, 73,378 of them (96 percent) filled out a questionnaire that asked them about other health conditions (comorbidities) and whether they had had PSA testing before random assignment to PSA testing or non-testing in this trial.

Crawford et al. have now combed through all these data to see if patients with at least one significant comorbidity who were randomized to the screening arm in the trial had a lower probability of prostate cancer-specific mortality [PCSM] than men with no or minimal comorbidity (with suitable adjustments for age and pre-study PSA testing).

The authors report the following results:

  • 9,565 deaths occurred in the screening arm of the trial at 10 years of follow-up.
  • 164/9,565 deaths were directly attributable to prostate cancer.
  • 22 prostate cancer-specific deaths occurred in men with no or minimal comorbidity randomly asigned to intervention versus usual care.
  • 38 prostate cancer-specific deaths occurred in men with one significant comorbidity randomly assigned to intervention versus usual care.
  • The adjusted hazard ratio [AHR] was 0.56, favoring men who had no or minimal comorbidity.
  • In this group of patients, the additional number needed to treat to prevent one prostate cancer-specific death at 10 years was only 5.
  • Among men with at least one significant comorbidity, those randomly assigned to intervention versus usual care did not have a decreased risk of PCSM (62 v 42 deaths; AHR = 1.43).

Now this type of post-study statistical analysis is interesting intellectually, and it may provide ideas for additional studies, but it can not be considered to provide conclusive proof of the idea that selective screening of men in good health does reduce risk for PCSM. Indeed, the authors are extremely careful to use the words “appears to reduce the risk of PCSM” in the conclusion to their abstract.

Quoted in a Reuters report on this newly published paper, one of the study authors (Dr. Anthony D’Amico) says that: “The reason why the original study appeared to be negative is it looked at all patients. What this study suggests is that PSA tests could be used more selectively in men who are in good health,” and that, ”For men who aren’t as healthy, it suggests that screening may not make a difference.” (Notice the careful use of words like “appeared,” “could,” and “may not” in this quote.)

In contrast, Ned Calonge, the chairman of the U.S. Preventive Services Task Force has noted that in this study the men who were less healthy and who were screened for prostate cancer seem to have had a higher risk of dying from prostate cancer than the less healthy men who weren’t screened, and it’s hard to explain that particular finding on any logical grounds.

Exactly what the PCLO trial continues to tell us at this time is that it was unable to show a definitive result favoring PSA-based screening of all men of 55 to 75 years of age for prostate cancer according to the trial protocol at 10 years of follow-up. All the analysis in the world isn’t going to be able to change that result. It can only help us to refine a potential hypothesis.

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