Our study yielded three key findings. First, we demonstrate the ability to accurately target and biopsy lesions seen on MRI using MR-US fusion technology in an office-based setting under local anesthesia. Second, the addition of targeted biopsies to systematic biopsies increases the rate of diagnosis of all cancers and, more importantly, Gleason ≥7 cancers. In fact, 38% of men with Gleason ≥7 cancers were detected only via targeted biopsies of lesions identified on MRI. Third, the level of suspicion on MRI correlated with both cancer diagnosis overall and diagnosis of Gleason ≥7 prostate cancers. Biopsies revealed CaP in 16/17 (94%) of men with an image grade 5 lesion on MRI.
Two recently published investigations utilizing different MR-US fusion devices for targeted prostate biopsy yielded similar results to ours. Pinto et al described a technique incorporating electromagnetic tracking and found cancer in 28%, 67% and 89% of men with low, moderate and high suspicion on MRI.9
Hadaschik et al incorporated MR-US fusion technology via a transperineal approach in the operating room and found CaP in 59% of men overall, and in 96% of men with highly suspicious lesions on MRI.10
The similarity of the above results to those presented here substantiates the advantages of image-guided targeted biopsy using MR-US fusion.
Other recent studies involved targeted prostate biopsy under direct MRI-guidance. Among 68 men with ≥2 prior negative TRUS biopsies and a median PSA of 13 ng/ml, Hambrock et al detected cancer in 59%.14
Of those with cancer, 45% had Gleason ≥7. The authors contrasted these results to a reference database at their institution in which the tumor detection rate during the third TRUS biopsy session (without MRI) was just 15%. The same group published results evaluating the concordance of highest Gleason grade (HGG) from biopsy to prostatectomy specimens in 98 patients. The exact concordance rate for MR-guided biopsy was 88% vs. 55% for TRUS-guided biopsy (p=0.001).8
In Germany, Anastasiadis et al performed MRI-guided biopsy on men with a suspicious MRI and ≥1 prior negative TRUS biopsy. The cancer diagnosis rate in 27 men (median PSA 10.2 ng/ml) was 55%.15
The present study applies a 5-point semi-quantitative scoring system to assess degree of cancer suspicion to lesions seen on MRI. The scoring system is based on T2 characteristics, quantitative apparent diffusion coefficient (ADC), and DCE curve analysis (). The scoring system, similar to that used by Hambrock,14
allows for graded levels of suspicion, as opposed to other protocols where a binary score of ‘normal’ or ‘abnormal’ was assigned.10, 15
Thus, the present scoring system follows guidelines recently released by the European Society of Uroradiology.13
Targeted prostate biopsy may be useful in three key situations: active surveillance, elevated PSA but negative TRUS biopsy, and selection for focal therapy. First, while surveillance has proven to be a safe approach for low risk CaP,16–21
utilization remains low22
and rates of progression to active treatment in the major surveillance series range from 14–41%.23
Targeted prostate biopsy may improve patient selection, making surveillance a more attractive option to patients while reducing progression to active treatment. Further, the tracking feature of the Artemis device allows the urologist to return to the exact area of prior positive biopsies, enabling the physician to follow individual tumors over time. Second, conventional TRUS biopsy may miss tumors in the apex and anterior prostate.2, 24, 25
MR-US fusion targeted biopsy may identify tumors missed by TRUS biopsy, sparing patients the discomfort of numerous negative biopsies and reducing the risk of delayed diagnosis of aggressive tumors. Our 37% diagnosis rate in the prior negative biopsy population, 67% of whom had Gleason ≥7 cancers, is considerably higher than would be expected from repeat conventional biopsy26, 27
and compares favorably with detection rates seen using saturation biopsy.28
Third, focal therapy has become an area of keen interest. Current strategies for patient selection for focal therapy often entail perineal template mapping biopsy,29
a more invasive, morbid, resource-intensive and expensive procedure than MR-US fusion biopsy.
This study has several limitations. First, given the low-risk patient population in our study (median PSA 4.9, all with prior biopsies), relatively few patients subsequently underwent radical prostatectomy. It remains possible that some significant tumors may be missed by both targeted and systematic biopsies. Whole-mount data would enable a more definitive analysis of the nature of lesions identified on MRI and biopsied using MR-US fusion. Second, while the yield of biopsies from image grade 5 lesions is excellent, the concordance between lower image grade lesions and biopsy histology is suboptimal. Further analysis may determine if this stems from inaccurate MR-US registration or if many abnormal areas on MRI are actually benign. Third, while some studies show a high sensitivity and specificity of contemporary multiparametric MRI,7, 30
prostate MRI remains difficult to interpret and requires dedicated training and expertise to approach the accuracy of expert radiologists. The yield of targeted biopsies relates directly to the ability of the radiologist to accurately identify targets on MRI. Until the sensitivity of prostate MRI is confirmed, we view the ability to obtain systematic biopsies along with targeted biopsies as an advantage of MR-US fusion technology over direct MRI-guided biopsy. Finally, image fusion technology is rapidly evolving and clinical experience with fusion devices remains in its infancy; advances in hardware and software are certain to change the usability of fusion devices in the future.
In spite of these limitations, MR-US targeted prostate biopsy has the potential to improve the contemporary diagnosis and treatment of CaP. The present data, obtained using an office-based procedure under local anesthesia, demonstrate better CaP detection than with systematic biopsies alone. These results compare favorably to those obtained using transperineal template biopsy techniques requiring general anesthesia. In contrast to direct MRI-guided biopsy, the present method allows both systematic and targeted biopsies to be obtained efficiently. Further work, including a detailed study correlating MRI, targeted biopsy results, and prostatectomy specimens, is ongoing.