Targeted prostate biopsies skew proportion of high-risk cases

By Liam Davenport, medwireNews Reporter

Image-targeted biopsy of the prostate leads to a substantial increase in the proportion of prostate cores identified as high risk compared with standard transrectal ultrasound (TRUS)-guided biopsy, the results of a UK study indicate.

"This could lead to inflation in risk attribution as a consequence of deliberate oversampling of one part of the prostate - in other words, targeting," say Nicola Robertson (Royal Free Hospital, London) and colleagues. "New risk stratification models may be required for men who have pathology derived from image-directed biopsy strategies."

They add in European Urology: "As a start to correct what could be regarded as an artefactual increase in cancer risk derived from targeted biopsy, a risk stratification system that is independent of the number of positive cores could be considered."

The team studied 107 consecutive radical prostatectomy whole-mount specimens in order to construct three-dimensional computer models. Systematic 12-core TRUS biopsy was subsequently compared with transperineal targeted biopsies of one to five cores, with a target defined as any lesion of at least 0.2 mL. High-risk cases were defined as a mean cancer core length (MCCL) of over 6 mm and/or more than 50% positive cores.

The team reports that TRUS biopsy detected 91% of 85 clinically significant cancers, compared with 98% with three targeted cores and 99% with four targeted cores. Targeted biopsies had a significantly higher proportion of positive cores, at 45% and 44% for three-core and four-core targeted biopsies, respectively, versus 11% for TRUS biopsies. Targeted biopsies also had significantly greater MCCLs, at 7.8 mm and 7.2 mm, respectively, versus 4.3 mm for TRUS biopsies.

Furthermore, 12-core TRUS biopsy correctly attributed high risk to 24% of clinically significant cases, compared with 66% using three-core targeted biopsies and 74% of four-core targeted biopsies. Targeted biopsies also demonstrated a higher disease burden in those cases that would be deemed clinically insignificant, defined as a Gleason score <7 and/or lesion size <0.5 mL.

The authors conclude: "Image-targeted biopsy results in an increase in risk attribution if traditional criteria, based on cancer core length and the proportion of positive cores, are applied. Targeted biopsy strategies will require new risk stratification models that account for the increased likelihood of sampling the tumour."

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