MRI-US fusion-guided biopsy for prostate cancer: data from the NCI Clinical Center

A newly published paper by the prostate cancer clinical research group at the National Cancer Institute (NCI) in Bethesda, Maryland, has reported on the use of magnetic resonance-ultrasound (MRI-US)-guided fusion biopsies, with specific emphasis on its value in men with larger prostates (i.e., prostates > 40 cm3 in volume).

In this paper by Walton-Diaz et al., the authors show that MRI-US fusion biopsy, which can be carried out as an office-based procedure, is particularly useful in identifying prostate cancer in men with larger prostates compared to standard TRUS-guided fusion biopsy — further endorsing the future potential of this technique (although, as the authors carefully note, “MR-US fusion technology requires a hefty initial investment and a need for technical support” that may limit its use to specialized prostate cancer centers).

Historic data suggest that, for men with prostates > 40 cm3 in volume who present for biopsy on suspicion on prostate cancer, the probability of a positive biopsy ≤ 30 percent. In this paper, Walton-Diaz et al. provide data from a series of nearly 800 MRI-US fusion-guided biopsies at the NCI Clinical Center in the 4-year period from January 2009 through December 2012. The MRI scans were all carried out using a 3.0 T MRI scanner and an endorectal coil, and were evaluated by two experienced uroradiologists who were blinded as to which scans were from which patients. It should also be noted that, prior to MRI-US fusion-guided biopsy, all patients underwent a multiparametric MRI scan, and only those with at least one suspicious lesion went on to have a biopsy.

What the research team was able to show was as follows:

  • 798 fusion biopsies were carried out altogether during the 4-year period.
  • 147/798 fusion biopsies were repeat fusion biopsies or were done on patients who had already received some form of prostate treatment, and were therefore excluded from this analysis.
  • For the 649 eligible patients having a first fusion biopsy
    • Average (mean) age was 61.8 ± 7.9 years.
    • Average (median) PSA level was 6.65 ng/ml.
    • Average (mean) whole prostate volume was 58.7 ± 34.3 cm3
    • 428/649 patients (65.9 percent) had had either no prior biopsy of any type or a negative result on prior biopsy (or biopsies).
    • 528/649 patients (81.4 percent) had had at least one prior TRUS-guided biopsy at another center.
    • 544/649 patients (83.8 percent) had no abnormal findings on DRE (and abnormal findings on DRE were not used to direct MRI-US fusion-guided biopsy).
    • 307/528 patients  who had had at least one prior TRUS-guided biopsy had no prior definitive finding of prostate cancer.
  • MRI-US fusion-guided biopsy was positive for cancer in
    • 357/649 patients (55.0 percent) overall
    • 128/307 patients (41.7 percent) who had had at least one prior TRUS-guided biopsy but no diagnosis of prostate cancer.
  • Both the patients’ ages and their prostate volumes were significantly associated with prostate cancer detection rates
  • When patients were stratified by prostate volume, prostate cancer detection rates were
    • 71.1 percent in men with a prostate volume of < 40.0 cm3
    • 57.5 percent in men with a prostate volume of 40.0 to 54.9 cm3
    • 46.9 percent in men with a prostate volume of 55.0 to 69.9 cm3
    • 46.9 percent in men with a prostate volume of 70.0 to 84.9 cm3
    • 33.3 percent in men with a prostate volume of 85.0 to 99.9 cm3
    • 36.4 percent in men with a prostate volume of 100.0 to 114.9 cm3
    • 30.4 percent in men with a prostate volume of ≥ 115.0 cm3
  • Prostate cancer detection rates showed a similar volume-related decline in
    • Men who had had prior negative TRUS-guided biopsies
    • Men who had had no prior diagnosis of cancer
  • The percentage of men being diagnosed with a Gleason score of 8 to 10 (about 20 to 25 percent) was similar regardless of prostate volume.

Now we have to be cautious about over-interpreting these results. The patients who end up going to a center like the NCI Clinical Center are a highly selected group and the data being presented here are from a retrospective, single-center analysis. Also, the authors point out in the full text of their paper that MRI-US fusion-guided biopsy can not be used to detect tumors that are ≤ 3 mm in diameter (a volume of about 0.015  cm3).

What this study does appear to do however, is the following:

  • Confirm that MRI-US fusion-guided biopsy can be to identify the presence of prostate cancer with a great deal more accuracy that systematic TRUS-guided biopsy (inclusive of TRUS-guided biopsies that may take up to 20 biopsy cores)
  • Suggest strongly that MRI-US fusion-guided biopsy may be particularly valuable in identifying prostate cancer in men with larger prostates — especially for those men with prostates between 40 and 85  cm3 in volume.

However, we also need to be very clear that this technology would increase the probability of identification of low-risk prostate cancers that may well not need treatment beyond some form of cautious monitoring, and some of the men being identified as having prostate cancer in this study might well have been better off if they had never had a biopsy at all because they were at no risk whatsoever for clinically significant prostate cancer.

We are still going to have to find better techniques to estimate clinical risk based on things like blood and urine samples, and then learn how to use sophisticated biopsy technology in the diagnosis of those men who really need that diagnosis!

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