In what may be the first study to evaluate the effect of PI-RADS v2.1 upgrading rules on magnetic resonance imaging (MRI) pathways for prostate cancer detection, researchers found the upgrading rules facilitate optimal clinical benefit for biopsy selection.
In the study, recently published in the American Journal of Roentgenology, researchers compared outcomes for five MRI-directed pathways for 716 patients (mean age of 64.9) with no known history of prostate cancer. The pathways included a biopsy-all pathway; an MRI-focused pathway; an MRI-focused pathway without upgrading; a risk-based pathway per guidelines; and a risk-based pathway without upgrading, according to the study. The study authors noted the cohort had a mean prostate-specific antigen (PSA) level of 6.1 ng/mL and a mean prostate volume of 51.3 mL.
The study authors noted no significant differences in the detection of clinically significant prostate cancer (csPCa) between the biopsy-all pathway and the other pathways. Looking at biopsy reduction, the researchers pointed to a 13 percent biopsy avoidance rate with the MRI focused pathway, 16 percent for the MRI-focused pathway without upgrading rules, 19 percent in risk-based pathways and 25 percent for the risk-based pathway without upgrading rules.
In assessing tradeoffs between csPCa detection and biopsy avoidance, the study authors found that disregarding PI-RADS upgrading rules in risk-based pathways resulted in one missed case of csPCa per 1.9 biopsies avoided. For MRI-focused pathways without upgrading rules, the researchers estimated 5.5 biopsies avoided per one missed case of csPCa.
“ … In the present evaluation, the number of biopsies avoided per missed csPCa did not represent a clinically acceptable tradeoff in either MRI-focused or risk-based pathways,” wrote lead study author Eduardo Thadeu de Oliveira Correia, M.D., Ph.D., who is affiliated with the Department of Radiology at University Hospitals Cleveland Medical Center in Cleveland, and colleagues.
Three Key Takeaways
1. PI-RADS v2.1 upgrading rules facilitate optimal clinical benefit for biopsy selection. The study suggests that adherence to PI-RADS v2.1 upgrading rules in magnetic resonance imaging (MRI) pathways for prostate cancer detection is associated with optimal clinical benefit in terms of biopsy selection.
2. Questionable tradeoff between clinically significant prostate cancer (csPCa) detection and biopsy avoidance rates. The study compared five different MRI-directed pathways and found varying rates of biopsy avoidance. Notably, the MRI-focused pathway without upgrading rules demonstrated a 16 percent biopsy avoidance rate, while the risk-based pathway without upgrading rules showed a higher rate of 25 percent. However, the study authors cautioned that neither MRI-focused pathways nor risk-focused pathways had clinically acceptable tradeoffs between biopsy avoidance and csPCa detection in the study.
3. Impact of ignoring PI-RADS upgrading rules on lesion frequencies. Disregarding PI-RADS upgrading rules resulted in a 34 percent increase in PI-RADS 2 lesions, a 42 percent increase in PI-RADS 3 lesions, and a 19 percent increase in PI-RADS 4 lesions. However, despite these increases, the study found no significant difference in the frequency of csPCa or Gleason grade > 3 prostate cancer between upgraded and dominant PI-RADS 4 lesions. This underscores the nuanced interpretation of PI-RADS lesions and emphasizes the need for further studies to assess inter-observer variability in assigning PI-RADS categories.
The researchers found that ignoring the PI-RADS upgrading rules resulted in a 34 percent increase in PI-RADS 2 lesions, a 42 percent increase in PI-RADS 3 lesions and a 19 percent increase in PI-RADS 4 lesions.
While the study authors pointed out a 40 percent higher frequency of prostate cancer (PCa) with dominant (no upgrading) PI-RADS 4 transition zone (TZ) lesions in comparison to upgraded PI-RADS 4 TZ lesions (87 percent vs. 47 percent), they noted no significant difference in csPCa frequency (33 percent vs. 26 percent).
The researchers also identified a 17 percent increase in PCa frequency with dominant PI-RADS 4 peripheral zone (PZ) lesions in contrast to upgraded PI-RADS 4 PZ lesions (84 percent vs. 67 percent), but there was no significant difference in csPCa or Gleason grade > 3 PCa frequencies.
“Per-patient analyses showed qualitatively similar results as in the per-lesion analyses with no significant differences in the frequencies of csPCa and off GG >3 PCa between dominant and upgraded PI-RADS 3 assessments, or between dominant and upgraded PI-RADS 4 assessments,” added Correia and colleagues.
(Editor’s note: For related content, see “Is MRI Overutilized in Prostate Cancer Imaging?,” “Positive Target of MRI: Could it be a Key Predictive Factor in Upgrading of Prostate Cancer Risk?” and “Emerging Predictive Model with mpMRI Findings May Reduce Up to 43 Percent of Unnecessary Systematic Prostate Biopsies.”)
Beyond the inherent limitations of a single center study, the authors noted the potential for patient selection bias stemming from all the cohort patient having a post-MRI biopsy. Acknowledging a lack of interobserver assessment in regard to use of the PI-RADS upgrading rules, the researchers emphasized the need for future studies to evaluate interobserver variability given the considerable variability between different facilities and radiologists with respect to PI-RADS category assignments.
