How many biopsy cores is the “right” number?

Back in the 1990s, it became customary to carry out prostate cancer biopsies under transrectal ultrasound (TRUS) guidance using the so-called “sextant” approach, under which six preplanned biopsy cores were taken from each of six specific areas of the prostate. In addition, the urologist might also take one or two additional cores from specific areas of the prostate that looked as though they might be cancerous on the ultrasound.

By the early years of the 21st century, it had become more common to take eight preplanned biopsy cores, and today most urologists would probably tell you that 10 or 12 biopsy cores taken from preplanned areas of the prostate was the “right” number for an initial biopsy. However, as far as we are aware, there has never been good evidence from randomized clinical trials to support this gradual “creep” in the number of biopsy cores.

This brings us to the data just published on line by Abd et al. in Urology.

Abd et al. wanted to know whether there was any difference in the results if one gave patients a biopsy based on eight biopsy cores as compared to 12 biopsy cores, so they carried out a study in just over 1,500 consecutive patients at the U.S. Veterans Administration Medical Center in Atlanta, Georgia.

The protocols for the 8-core and the 12-core biopsies were targeted such that all cores would come from the the peripheral (outer) zone of the prostate. The study was designed to compare rates of cancer detection based on the two protocols, the characteristics of the cancers, and the sensitivity of the two protocols in selected subgroups of men.

Here is what they were able to show:

  • The total number of men biopsied was 1,546.
  • The overall rate of positive biopsies was 49.9 percent.
  • The rate of positive biopsies using the 8-core protocol was  51.2 percent.
  • The rate of positive biopsies using the 12-core protocol was  49.2 percent.
  • There was no significant difference between the results of the two biopsy protocols.
  • Advanced age and high body mass index were significantly associated with higher likelihood of a positive biopsy result.
  • Larger prostate volumes were associated with lower probability of a positive biopsy result.

The authors conclude that “there was no evidence that 12-core biopsy improved the likelihood of prostate cancer diagnosis compared with 8-core biopsy” and that “the results of this cohort from a US veteran population suggest that targeting the peripheral zone is more important than the absolute number of biopsy cores.” They go on to note, however, that in, for example, men with very large prostates (and some other specific clinical characteristics), more than eight biopsy cores cores may be advisable.

Should we expect every urologist in America to revert to 8-core biopsies tomorrow? Probably not. Should someone else repeat this study to see if they get a similar result? Probably. (It wouldn’t actually take that long if three or four large centers were to collaborate.) We should, of course, point out that while this trial was randomized it certainly wasn’t blinded. Each urologist knew exactly how many cores he needed to take from each patient!

[Editorial note: We have not yet seen the full text of this paper. However, since the text above was written, we have been advised that the patients were not in fact randomized to an 8- or a 10-core biopsy, they were simply biopsied sequentially, and that there are some noticeable differences between the two cohorts of patients. We are seeking a complete copy of the paper to get additional insight.]

The other thing that is interesting about this study is that the rate of positive biopsies was of the order of the 50 percent. Historically, positive biopsy rates of 20 to 40 percent in “screening” populations has been considered to be closer to the norm. Does this say something about the age and body mass index of veterans presenting for biopsy in Atlanta? Or does it tell us that the Atlanta VA Medical Center is better than average at deciding which patients really are appropriate for a biopsy?

One Response

  1. A single biopsy is enough impact …
    Why not use magnetic resonance equipment?
    Too expensive?
    What is the cost of a life?
    I guess that biopsy is a great deal to some doctors.

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