By: Dan Sperling, MD

Conventional transrectal ultrasound-guided (TRUS) biopsy continues to be the dominant method of sampling the prostate gland when prostate cancer (PCa) is suspected. In addition to being the “gold standard” since its use began in the 1980s, it is relatively economical. It is typically done in the setting of a urology practice using portable equipment. However, because it is blind to tumor tissue vs. healthy tissue, biopsy needles are placed according to a systematic plan (usually 6-7 needles per each side of the gland for a total of 12-14 cores) rather than aimed at a lesion. This confers a random quality to the procedure. Problems with TRUS biopsy include:

  • Missing up to 30% of tumors, especially at the anterior and apical areas
  • Underdetection of significant prostate cancer (PCa) defined as Gleason score > 7
  • Overdetection of insignificant prostate cancer (Gleason score < 6) that does not require immediate treatment but which can still provoke anxiety in the patient
  • Risk of infection that increases with the number of needles used
  • Risk of side effects, including urinary and sexual problems

MRI-guided targeted biopsy is an alternative to blind TRUS biopsy. Many urologists recognize the advantages of magnetic resonance imaging (MRI), particularly functional or multiparametric MRI (mpMRI), for detecting and characterizing suspicious lesions within the prostate. A growing number of urologists are turning to a novel technology called ultrasound/MRI fusion imaging. It involves software-based co-registration (“merging”) of previously captured MRI scans with real-time ultrasound. Fusion imaging brings MRI results into the urology practice, and fusion-guided targeted prostate biopsies are becoming more common. However, the most accurate targeted prostate biopsies are gained using real-time MRI guidance, performed in the bore of the magnet. This procedure is offered in radiology centers rather than urology practices, and has demonstrated superiority over fusion-guided biopsies. (For more information on this, see https://sperlingprostatecenter.com/mri-targeted-biopsy-real-time-in-bore-biopsy-is-best/.)

A recent article published in Academic Radiology by Garmer et al. underscores the improved accuracy of real time in-bore targeted biopsy over that of TRUS. The authors draw particular attention to the overdetection of insignificant PCa when 12 or more TRUS-guided needles are used. Their purpose was to test the Gleason score accuracy of fewer needles used in pre-prostatectomy MRI-targeted biopsy when correlated with the surgically removed prostate specimens (histopathology).

Their study involved 50 prostate cancer patients who underwent multiparametric MRI involving four imaging sequences (T2-weighted, diffusion-weighted, dynamic contrast enhanced, and spectroscopy) done with an endorectal coil. The image interpretations included the use of the PI-RADS 5-point scoring system (learn more at https://sperlingprostatecenter.com/pi-rads-score/) Suspicious lesions with scores of > 3 were targeted on biopsy; the median number of needles was 4 (range 2-6) with a median of 2 positive cores per biopsy (range 1-4). The biopsy Gleason scores were recorded. When compared with the histopathology results, post-surgical upgrading or downgrading was evaluated, and upgrading from Gleason 6 to Gleason 7 was defined as significant.

Histopathology revealed that 20% of patients had Gleason 6 cancer. The biopsy-obtained Gleason score was concordant in 66% of the patients. Overall upgrading compared with the MRI biopsies occurred in 30% of the patients (PI-RADS underestimated the cancer), and 4% of patients were downgraded (PI-RADS overestimated the cancer). The authors note, “Significant upgrading of the Gleason score from 6 to 7 occurred in eight patients; upgrading did not exceed one step in the Gleason score.”

The authors concluded that “in-bore MRI-targeted biopsy offers good accuracy in the Gleason score with postprostatectomy histopathologic control…” What is important is the limited number of needles used to gain accurate information, when compared against a 10-12 core TRUS biopsy with higher rates of false negative results (leading to repeat biopsies) and overdetection of indolent PCa. They point out the low detection rate of insignificant PCa with in-bore biopsy, and that the upgrading in their population was restricted to one step in the Gleason score. They emphasize the need for greater physician awareness of in-bore biopsy as clinically advantageous.

Other authors who have written on the merits of in-bore biopsy have offered economic calculations showing that one accurate real-time MRI-guided targeted biopsy compares favorably against the cumulative expense over time of repeat TRUS biopsies and the cost of managing biopsy-related side effects. There is another cost to the patient who undergoes repeat biopsies: the risk of PCa growth and progression until the tumor is virtually impossible to miss on TRUS biopsy, which puts the patient at risk of missing a curative treatment window.

When all this is taken into account, in-bore targeted biopsy appears to be in the patient’s best interest.

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