Evaluating Biparametric Versus Multiparametric Magnetic Resonance Imaging for Diagnosing Clinically Significant Prostate Cancer: An International, Paired, Noninferiority, Confirmatory Observer Study

Abstract

Background and objective: Biparametric magnetic resonance imaging (bpMRI), excluding dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI), is a potential replacement for multiparametric MRI (mpMRI) in diagnosing clinically significant prostate cancer (csPCa). An extensive international multireader multicase observer study was conducted to assess the noninferiority of bpMRI to mpMRI in csPCa diagnosis.

Methods: An observer study was conducted with 400 mpMRI examinations from four European centers, excluding examinations with prior prostate treatment or csPCa (Gleason grade [GG] ≥2) findings. Readers assessed bpMRI and mpMRI sequentially, assigning lesion-specific Prostate Imaging Reporting and Data System (PI-RADS) scores (3-5) and a patient-level suspicion score (0-100). The noninferiority of patient-level bpMRI versus mpMRI csPCa diagnosis was evaluated using the area under the receiver operating curve (AUROC) alongside the sensitivity and specificity at PI-RADS ≥3 with a 5% margin. The secondary outcomes included insignificant prostate cancer (GG1) diagnosis, diagnostic evaluations at alternative risk thresholds, decision curve analyses (DCAs), and subgroup analyses considering reader expertise. Histopathology and ≥3 yr of follow-up were used for the reference standard.

Key findings and limitations: Sixty-two readers (45 centers and 20 countries) participated. The prevalence of csPCa was 33% (133/400); bpMRI and mpMRI showed similar AUROC values of 0.853 (95% confidence interval [CI], 0.819-0.887) and 0.859 (95% CI, 0.826-0.893), respectively, with a noninferior difference of -0.6% (95% CI, -1.2% to 0.1%, p < 0.001). At PI-RADS ≥3, bpMRI and mpMRI had sensitivities of 88.6% (95% CI, 84.8-92.3%) and 89.4% (95% CI, 85.8-93.1%), respectively, with a noninferior difference of -0.9% (95% CI, -1.7% to 0.0%, p < 0.001), and specificities of 58.6% (95% CI, 52.3-63.1%) and 57.7% (95% CI, 52.3-63.1%), respectively, with a noninferior difference of 0.9% (95% CI, 0.0-1.8%, p < 0.001). At alternative risk thresholds, mpMRI increased sensitivity at the expense of reduced specificity. DCA demonstrated the highest net benefit for an mpMRI pathway in cancer-averse scenarios, whereas a bpMRI pathway showed greater benefit for biopsy-averse scenarios. A subgroup analysis indicated limited additional benefit of DCE MRI for nonexperts. Limitations included that biopsies were conducted based on mpMRI imaging, and reading was performed in a sequential order.

Conclusions and clinical implications: It has been found that bpMRI is noninferior to mpMRI in csPCa diagnosis at AUROC, along with the sensitivity and specificity at PI-RADS ≥3, showing its value in individuals without prior csPCa findings and prostate treatment. Additional randomized prospective studies are required to investigate the generalizability of outcomes.

Keywords: Biparametric magnetic resonance imaging; Dynamic contrast-enhanced imaging; Multiparametric magnetic resonance imaging; Noninferiority; Observer study; Prostate cancer.

Fig. 1 –

Flow diagram illustrating patient-level PI-RADS scores at biparametric (bp) and multiparametric (mp) MRI, encompassing all readings within the observer study (n = 6174). The diagram depicts intrareader consistency, and upgrades or downgrades between bpMRI and mpMRI assessments. The left side represents bpMRI readings, while the right side represents mpMRI readings. Arrows indicate upgrades and downgrades from bpMRI to mpMRI. Each category includes the number of readings, percentages, and its clinically significant prostate cancer (csPCa) prevalence. For 91% of readings (n = 5630), bpMRI and mpMRI yielded the same patient-level PI-RADS score. A minority of readings involved patients initially classified with a PI-RADS <3 score at bpMRI, and subsequently upgraded to PI-RADS 3 (n = 57 [<1%], with 19% csPCa), PI-RADS 4 (n = 77 [1%], with 22% csPCa), and PI-RADS 5 (n = 9 [<1%], with 56% csPCa) with mpMRI. Another significant group comprised readings initially assigned an equivocal grade (PI-RADS = 3) but were subsequently upgraded to a PI-RADS score of ≥4 (n = 206 [3%], with 29% csPCa) and 5 (n = 10 [<1%], with 50% csPCa). At mpMRI, there was an overall decrease in equivocal PI-RADS = 3 scores of 3% (from 14% to 11%). MRI = magnetic resonance imaging; P/PI-RADS = Prostate Imaging Reporting and Data System.

Fig. 2 –

Decision curve analysis for diagnosing clinically significant prostate cancer (csPCa) with biparametric (bp) and multiparametric (mp) MRI across three different risk thresholds. Threshold probabilities range from 5% to 30%, representing the willingness to conduct biopsies to diagnose one case of csPCa. Lower thresholds represent cancer-averse scenarios, while higher thresholds indicate biopsy-averse scenarios. The net benefit (NB) is defined as the true positive count corrected for false positives, weighted by the odds of the threshold probability. Across thresholds, mpMRI at PI-RADS ≥3, mpMRI at PI-RADS ≥4 and PI-RADS 3 with prostate-specific antigen density (PSAd) of ≥0.15 ng/ml², as well as bpMRI at PI-RADS ≥4 and PI-RADS 3 with PSAd of ≥0.15 ng/ml² exhibited the highest NB. Differences in NB between pathways were small. At an European Association of Urology–recommended 10% probability threshold [5], the NB difference between bpMRI and mpMRI at PI-RADS ≥3 was 0.002, indicating that 1/0.002 = 500 mpMRI examinations are needed to diagnose one additional csPCa case compared with a bpMRI protocol. MRI = magnetic resonance imaging; PI-RADS = Prostate Imaging Reporting and Data System.