Predictive accuracy of the new ISUP grading system in a nationwide patient cohort


A paper in European Urology has provided us with additional early data on the applicability of the new ISUP grading system scheduled to replace the Gleason grading system over the next few years.

Loeb et al. used data from the Swedish National Prostate Cancer Registry to identify nearly 6,000 men from a nationwide patient cohort, all diagnosed with prostate cancer between 2005 and 2007 (of whom > 4,000 were treated by radical prostatectomy and about 1,500 by radiation therapy). They then used the new ISUP grading system to examine its ability to predict patients’ biochemical outcomes after treatment and compare those predictions to the patients’ actual outcomes.

To get the details about the new ISUP grading system, please see the link above, but basically, under the new system

  • An ISUP grade of 1 is equivalent to a Gleason score of 3 + 3 = 6 or less
  • An ISUP grade of 2 is equivalent to a Gleason score of 3 + 4 = 7
  • An ISUP grade of 3 is equivalent to a Gleason score of 4 + 3 = 7
  • An ISUP grade of 4 is equivalent to a Gleason score of 4 + 4 = 8
  • An ISUP grade of 5 is equivalent to a Gleason score of 9 or 10

Here is what Loeb and her colleagues report:

  • Average (median) follow-up for their patient cohort was 4.6 years.
  • Among the 4,325 men who had surgery,
    • Based on ISUP grades at time of biopsy, the 4-year biochemical recurrence-free survival rates were
      • 89 percent for men with an ISUP grade of 1
      • 82 percent for men with an ISUP grade of 2
      • 74 percent for men with an ISUP grade of 3
      • 77 percent for men with an ISUP grade of 4
      • 49 percent for men with an ISUP grade of 5
    • Based on ISUP grades at pathological examination post-surgery, the 4-year biochemical recurrence-free survival rates were
      • 92 percent for men with an ISUP grade of 1
      • 85 percent for men with an ISUP grade of 2
      • 73 percent for men with an ISUP grade of 3
      • 63 percent for men with an ISUP grade of 4
      • 51 percent for men with an ISUP grade of 5
  • Among the 1,555 men who had radiation therapy,
    • Based on ISUP grades at time of biopsy, the 4-year biochemical recurrence-free survival rates were
      • 95 percent for men with an ISUP grade of 1
      • 91 percent for men with an ISUP grade of 2
      • 85 percent for men with an ISUP grade of 3
      • 78 percent for men with an ISUP grade of 4
      • 70 percent for men with an ISUP grade of 5
  • After adjustment for PSA level and clinical stage at diagnosis, the biopsy-based ISUP grades were significant independent predictors of biochemical recurrence after radical prostatectomy and radiation therapy.
  • The new ISUP system resulted in virtually no change in predictive accuracy compared with the current three- and four-tier risk classifications (e.g., very low, low, intermediate, and high risk)
  • The median follow-up of only 4.6 years made it impossible to examine any impact of use of the ISUP grading system on long-term oncologic outcomes.

Loeb and her colleagues conclude that the new ISUP grading system offers

a simplified, user-friendly nomenclature to aid in patient counseling, with similar predictive accuracy in a population-based setting to previous classifications.

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