Based on the standard five-letter grading system (A, B, C, D, F), getting your report card may or may not have been a time of dread. However, that system did not raise every kid’s anxiety until its universal adoption by U.S. schools in the 1940s. Were you ever curious as to why the letter E is not included in the sequence of five letter grades? You’ll find the answer at the end of this blog*, but in case you’ve wondered why 5 was the magic number of grades instead of 3, 7, 10 or some other number? Well, five seems to be just right for covering our understanding from best to worst.
For instance, 5-star ratings are commonplace. We use them for movies, products, customer service—just about anything you can name. Five makes it easy and efficient to cover a potentially limitless range of subjective experiences. For example, the typical opinion survey might use the following five labels:
- Strongly disagree
- Disagree
- Neutral
- Agree
- Strongly agree
As humans, we love five simple levels that efficiently standardize what we seek to measure.
5-Level Systems in Prostate Cancer
The world of prostate cancer (PCa) has widely adopted two 5-level systems that are used by clinicians and patients alike:
1. The ISUP (International Society of Urological Pathology) Grade Group (GG) based on biopsy is gradually replacing the Gleason grade 2-number sum because it’s easier to understand.
| GG | Risk Level |
| 1 | Low risk (PCa is likely to be slow growing and unlikely to spread) |
| 2 | Favorable intermediate risk (PCa moderately unlikely to spread) |
| 3 | Unfavorable intermediate risk (PCa moderately likely to spread) |
| 4 | High risk (PCa likely to be fast growing and spread) |
| 5 | Highest risk (PCa most likely to grow and spread) |
2. PI-RADS (Prostate Imaging Reporting and Data System) based on multiparametric MRI (mpMRI) is designed to rate the probability that significant PCa is present on imaging.
| PI-RADS Score | Probable Presence of Clinically Significant PCa |
| 1 | Highly unlikely |
| 2 | Unlikely |
| 3 | May or may not be present |
| 4 | Likely |
| 5 | Highly likely |
In addition to the now-standard systems above, which improve the diagnosis of PCa in an untreated prostate, a new mpMRI-based system for “detection or characterization of residual or recurrent disease in the treated prostate”[i] was proposed by a consensus panel of experts in 2021.[ii] Called the Prostate Imaging for Recurrence Reporting (PI-RR) system, it instructs on image capture using two parameters (Diffusion Weighted Imaging and Dynamic Contrast Enhancement), and scores the probability that clinically significant PCa is present following treatment.
| PI-RR Score | Probable Presence of Clinically Significant PCa |
| 1 | Very low likelihood |
| 2 | Low likelihood |
| 3 | Uncertain likelihood (may or may not be present) |
| 4 | High likelihood |
| 5 | Very high likelihood |
PI-RR is being tested for accuracy and reproducibility of interpretation in clinical studies. Recently, a multi-institutional group reviewed six studies published since 1921 (total of 467 patients) that reported PI-RR diagnostic performance. Based on their analysis of accuracy at a PI-RR cutoff score of 3 or greater, the authors’ 2024 published paper concluded, “PI-RR is accurate in detecting local recurrence after whole-gland treatment for prostate cancer and shows fair-to-good to excellent inter-reader agreement. Overall, a PI-RR cutoff of ≥3 showed high sensitivity and specificity.”[iii]
It’s a safe bet that PI-RR, like its cousins ISUP GG and PI-RADS systems, will achieve broad adoption, and benefit patients by aiding early MRI identification of localized PCa recurrence after ablation or radiation.
*Now, as promised at the beginning of this blog, if you want to know why U.S. school grades omit the letter E, mastersportal.com says:
Back in 1897, the letter E used to mean the same thing as F; that is, it used to be the lowest possible grade. However, parents and students found it easier to understand that “F” stood for “Failed” (rather than thinking that “E” could mean “excellent”). Since the 19th Century, the letter F has come to universally mean “Failed”, and has incidentally become the letter that every student fears.
References
[i] Margolis DJA. Editorial Comment: Posttreatment Prostate MRI Is Not “RAD”… It’s “PIRRfect”. AJR Am J Roentgenol. 2023 Jun;220(6):862.
[ii] Panebianco V, Villeirs G, Weinreb JC, Turkbey BI et al. Prostate Magnetic Resonance Imaging for Local Recurrence Reporting (PI-RR): International Consensus -based Guidelines on Multiparametric Magnetic Resonance Imaging for Prostate Cancer Recurrence after Radiation Therapy and Radical Prostatectomy. Eur Urol Oncol. 2021 Dec;4(6):868-876.
[iii] Mourato FA, Schmitt LG, Mariussi M, Torri G et al. Prostate Magnetic Resonance Imaging Using the Prostate Imaging for Recurrence Reporting (PI-RR) Scoring System to Detect Recurrent Prostate Cancer: A Systematic Review and Meta-analysis. Eur Urol Oncol. 2024 May 31:S2588-9311(24)00137-8.
About Dr. Dan Sperling
Dan Sperling, MD, DABR, is a board certified radiologist who is globally recognized as a leader in multiparametric MRI for the detection and diagnosis of a range of disease conditions. As Medical Director of the Sperling Prostate Center, Sperling Medical Group and Sperling Neurosurgery Associates, he and his team are on the leading edge of significant change in medical practice. He is the co-author of the new patient book Redefining Prostate Cancer, and is a contributing author on over 25 published studies. For more information, contact the Sperling Prostate Center.
