Role of MRI in low-risk prostate cancer: Finding the Wolf in sheep's clothing or the sheep in Wolf's clothing?

Purpose of review In men on active surveillance for localized prostate cancer, MRI and MRI-targeted biopsies can be used prior to confirmatory or surveillance biopsy, to detect individuals with high-grade cancer (the wolf in sheep's clothing). However, some men will have low-risk disease despite adverse MRI findings (the sheep in wolf's clothing). We review the value addition of MRI-targeted biopsies in comparison to systematic transrectal ultrasound-guided biopsies, using pathological reclassification as an end-point. Recent findings At confirmatory and surveillance biopsies, both the MRI-targeted and repeat standard biopsies have shown value in identifying histologically adverse findings in men with low-risk prostate cancer. For maximal detection of clinically significant cancer, a prebiopsy MRI should be performed together with both MRI-targeted and systematic transrectal ultrasound-guided biopsies. Stable disease on MRI may reduce the need for serial biopsies in some men on active surveillance. Summary Prostate MRI and subsequent MRI-targeted biopsies are worthwhile to the current management of men with low-risk prostate cancer on active surveillance. Prostate MRI, in combination with a multivariable risk-prediction model may help in identifying both the wolf in sheep's clothing and the sheep in wolf's clothing, and in potentially reducing the need for serial biopsies.

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