The Tuesday news update: October 28, 2008

Many reader will already have seen or heard reports of the demise of the SELECT prostate cancer prevention trial. In other news today:

  • There is a recent review of trials of diet and dietary supplements
  • Further evidence supports the potential of surrogate markers for prostate cancer mortality
  • Saturation biopsies appear to overestimate the risk of prostate cancer

Van Patten et al. have published a timely review of data on clinical trials of diet and/or dietary supplements and their impact on prostate cancer progression, recurrence and survival. Of the 32 studies that met their review criteria, only 9 were randomized, controlled trials. They note that significant decreases in PSA levels have been observed in studies using a low fat vegan diet, soy beverage or lycopene supplementation. However, a significant increase in PSA doubling time was also observed in a study on lycopene supplementation. In only one randomized, controlled trial (in men undergoing orchiectomy) was a survival end point of fewer deaths with lycopene supplementation reported. The authors appear to imply that larger and better designed trials are needed to assess the potential of diet modificiation and selected dietary supplements in the management of prostate cancer.

Denham et al. have reported on a retrospective anaysis of data from a major Austalian study to further propose the potential of time to biochemical failure (TTBF) and PSA doubling time (PSADT) as surrogate endpoints for prostate cancer clinical trials (at least in patients treated with radiotherapy). Their data appears to support this potential. However, it would require large, randomized, multi-center trials over many years to establish the real validity of these surrogate endpoints (as the authors clearly acknowledge). Denham et a. suggest the use of large meta-analyses as an interim step toward the further establishment of the accuracy of these surrogate endpoints.

Finally, Delongchamps et al. have demonstrated that while standard 12-core biopsies tend to underestimate risk for prostate cancer, a 36-core saturation biopsy tends to overestimate that risk. They demonstrated this finding by biopsying the prostates of 48 autopsy specimens in men who had died for other reasons, with no prior history of prostate cancer. Quite what to make of these findings it is difficult to say. As the authors themselves have noted in a follow-up comment, “Studies evaluating prostate cancer detection are influenced by verification bias. The reference standard investigation is not performed on all patients, since those with a low PSA level do not undergo prostate biopsy and those for which prostate biopsy failed to detect cancer do not undergo surgical verification. Thus, the true sensitivity of biopsy regimens is difficult to estimate.” What is clear from this study is that prostate biopsy is by no means the ideal method for diagnosing clinically significant prostate cancer (but then we probably knew that already!)

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: