MRI/TRUS fusion-guided biopsies and the diagnosis of prostate cancer

An important article by Siddiqui et al. appears in this week’s issue of the Journal of the American Medical Association. It deals with the experience of Dr. Peter Pinto and his colleagues in the diagnosis of prostate cancer in about 1,000 patients over the past few years. The article is also discussed on the ScienceDaily web site.

Between 2007 and 2014, at the National Cancer Institute’s Clinical Center in Bethesda, Dr. Pinto and his colleagues carried out standard systematic biopsies and targeted MRI/ultrasound fusion biopsies on a prospective cohort of 1,003 eligible men who had been referred to their center (usually because of an elevated PSA or an abnormal rectal exam).  Well over half of these men had already had at least one previous, negative, standard prostate biopsy.

For interested readers, the entire text of this article is available on line, and it is certainly worth printing out a copy for your files if you are support group leader or other prostate cancer educator.

So what do Dr. Pinto and his colleagues report based on their 7 years of experience?

All the 1,003 patients were given

  • A 3-T, multi-parametric prostate MRI to identify regions of the prostate that appeared suspicious for prostate cancer
  • A targeted MRI/TRUS fusion-guided biopsy and
  • A concurrent, standard, systematic biopsy

The primary goal was to compare the accuracy of targeted and standard biopsy approaches for the detection of high-risk prostate cancer (defined as the presence of any cancer with a Gleason score of 4 + 3 = 7 or higher). Secondary goals were related to the accuracy of detection of lower risk forms of prostate cancer (with Gleason scores of 3 + 4 = 7 and below) and the ability of the different types of biopsy to predict actual whole-gland pathology at radical prostatectomy (whenever this was possible).

Here are the important findings:

  • Targeted MRI/TRUS fusion biopsy alone diagnosed prostate cancer in 461 cases.
  • Standard, systematic biopsy alone diagnosed prostate cancer in 469 cases.
  • There was exact agreement between the results of targeted and standard biopsies in 690/1,003 men (69 percent).
  • Targeted biopsies diagnosed
    • 30 percent more high-risk cancers than standard biopsies (173 vs 122 cases, P < 0.001)
    • 17 percent fewer low-risk cancers than standard biopsies (213 vs 258 cases, P < 0.001).
  • Combining data from the standard biopsy cores with the data from the targeted cores identified an additional 103 cases of prostate cancer.
    • 83 percent of these were low-risk disease.
    • 12 percent of these were intermediate-risk disease.
    • 5 percent of these were high-risk disease.
  • Incorporation of a standard biopsy in addition to a targeted biopsy led to no change in Gleason score risk stratification in 857/1,003 cases (85 percent).
  • The predictive ability of targeted biopsy to differentiate low-risk from intermediate- and high-risk disease in 170 men with whole-gland pathology after prostatectomy was greater than that of standard biopsy or of the two approaches combined.

However, what Siddiqui et al. do not conclude is that all men suspected of being at risk for prostate cancer should now be having an MRI/TRUS fusion-guided biopsy. Rather, they state the following:

Among men undergoing biopsy for suspected prostate cancer, targeted MR/ultrasound fusion biopsy, compared with standard extended-sextant ultrasound-guided biopsy, was associated with increased detection of high-risk prostate cancer and decreased detection of low-risk prostate cancer. Future studies will be needed to assess the ultimate clinical implications of targeted biopsy.

An editorial by Schwartz and Basch in the same issue of JAMA appears to be supportive of that conclusion — although only part of that editorial is available on line.

While it is certainly tempting to see these data from the NCI Clinical Center as giving a definitive “green light” to the widespread use of MRI/TRUS fusion biopsies in the diagnosis of prostate cancer, the authors themselves point out several reasons why this would be inappropriate, including all of the following:

  • The fact that this was a pilot, single-institution study in which most of the patients had already had at least one negative biopsy, leading to the potential for selection bias among patients enrolled.
  • The fact that any patient with an MRI result that showed no lesion suspicious for risk of prostate cancer was ineligible for the study.
  • The costs associated with acquisition and use of the specialized technology necessary.
  • The fact that all multi-parametric MRIs taken in this trial were evaluated for risk of prostate cancer by two highly experienced genitourinary radiologists, and such sub-specialists are currently relatively few and far between.

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