Introduction:

Multiparametric MRI fusion biopsy can increase detection of clinically significant prostate cancer compared to standard systematic biopsy in men with low-risk prostate cancer. Men on active surveillance (AS) undergo multiple MRIs. Less is known about the stability of MRI PIRADS v.2 scoring over time and whether change in PIRADS score predicts biopsy upgrade or progression for men on active surveillance.

Methods:

In a retrospective review of an institutional database, we identified men diagnosed with clinically localized prostate cancer, CAPRA score less than or equal to 5, absence of Gleason 5, two MRIs within three years of initial diagnosis, and initially  managed with AS. Upgrade was defined as increase in biopsy Gleason grade to 3+4 or greater. Progression was defined as increase in biopsy Gleason grade and percentage positive cores. Cox proportional hazards regression was used to identify factors associated with the outcomes of interest.

Results:

193 men were evaluated in this study. Median time between MRIs was 19 months (range 8-36 months). Median follow up was 69 months (range 19-218 months). At MRI 1, 20% of patients had PIRADS 1-2 lesions, 21% PIRADS 3, and 48% PIRADS 4 or 5. At MRI 2, 13% of patients had PIRADS 1-2 lesions, 14% PIRADS 3, and 74% PIRADS 4 or 5. PIRADS score increase (from 1-3 to 4 or 5) occurred in 30% of patients.  Only 18% of PIRADS 3 lesions remained stable on subsequent MRI; 74% increased to PIRADS 4 or 5 (51 and 23% respectively). 70% of PIRADS 4 lesions stayed PIRADS 4 and 14% increased to PIRADS 5. 65% of PIRADS 5 lesions remained PIRADS 5. At MRI 1, PIRADS 5 was predictive of biopsy upgrade (HR 2.4 95% CI 1.0-5.8, p=0.04), but not PIRADS 4 (p=0.42), when compared to PIRADS 1-3. At MRI 2, however, both PIRADS 4 and 5 were associated with biopsy upgrade (HR 2.7 95% CI 1.2-5.8 p=0.01; HR 4.8 95% CI 2.2-10.6, p<0.01, respectively) when compared to PIRADS 1-3. PIRADS 5 was associated with biopsy progression at both MRI 1 and MRI 2 (HR 2.6 95% CI 1.1-3.8, p=0.02; HR 4.3 95% CI 1.8-10.3, p<0.01, respectively), but not PIRADS 4 (p=0.89, 0.17). Overall PIRADS increase between MRI 1 and MRI 2 was associated with biopsy upgrade (HR 2.7, 95% CI 1.8-6.3), but not progression.

Conclusion:

There is a high incidence of PIRADS score increase between prostate MRIs on men on active surveillance, which is associated with biopsy upgrade. Furthermore, PIRADS 4 and 5 lesions are more predictive of biopsy upgrade and progression at second MRI when compared to first MRI. Additional study into the role of MRI fusion biopsy for men on active surveillance is necessary. 

Funding: N/A