Several questions are still unanswered regarding the application of AS at first time diagnosis and the reclassification of risk during follow-up on AS. These include the dilemma whether to consider AS based on TRUS biopsies only or on targeted MRI guided biopsies, or on both. Additionally, it is not clear what role MRI takes in the follow-up of AS patients. MRI has been shown to improve accuracy for relevant cancers after first negative TRUS biopsy and results are still pending on whether it is useful in the setting of increased cancer risk, before first biopsy (PRECISION and other studies). Confirmational MRI at the start of AS shows upgrading of cancer by analysis of targeted biopsies in 20% of cases. This provides benefit in reducing delay in reclassification.
A study looking specifically at the role of MRI in AS patients showed that omission of a biopsy is a reasonable approach if PSA density is below 0.15 and the MRI shows only a PIRADS 3 lesion. This can reduce unnecessary targeted biopsies by ~50%, without missing any result of Gleason 7 (3+4) disease and above. Using MRI can also delay treatment shift in AS patients by performing an MRI targeted biopsy instead of active treatment when biopsy results show 2 or more positive cores and/or a PSA doubling time < 3 years. Moreover, if the PSA density is over 0.15, a PIRADS 5 lesion exists or initial Gleason was 7 (3+4), these all trigger performing an MRI.
However, MRI is not exempt from limitations. These include underestimation of tumor volume, harboring only a moderate association between diffusion weighted imaging and Gleason score, no available correlation between genomic/biologic and radiologic MRI classification of prostate cancer lesions, and no available criteria for lesion dynamics.
In conclusion, confirmatory biopsies being performed as systematic biopsies together with MRI targeted biopsies substantially improves misclassification of men previously selected for AS based on systematic biopsies only.
If PSA density is below 0.15 and there is only a PIRAD 3 lesion, it is reasonable to consider omitting a targeted biopsy. PSA doubling time less than 3 years and more than 2 cores positive should trigger an MRI with targeted biopsy instead of active treatment. To this day, MRI cannot replace biopsies in AS and personalized surveillance is needed instead of a one size fits all protocol.
Dr. Bangema ended the presentation with his recommendation to use prostate MRI+targeted biopsy in these circumstance:
1. When selecting patients for AS based only on TRUS biopsies
2. When reclassifying patients during AS, if they had no previous MRI, and if they have a PIRADS lesion 3 and above.
Presented by: Dr. Chris .H. Bangma, Rotterdam (NL)
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto
at the #EAU17 -March 24-28, 2017- London, England