Although prostate biopsies are becoming less random and more systematic, cancer is still being missed. The current standard of care practice for an initial biopsy involves taking 10 to 14 cores and detects prostate cancer 27% to 40.3% of the time.2–6
Some physicians are moving toward saturation biopsy techniques with the hope of improving cancer detection. Studies have shown that there is no difference between the cancer detection rate of standard and saturation biopsies in biopsy naïve patients.7,22
Although the number of cores may be increased, biopsies are still not directed toward cancer. Prostate cancer remains the only tumor sampled with the hope of hitting tumor. However, saturation biopsies may have a role in detecting cancer at a rate of 29% to 41% in patients with a suspicion for cancer and prior negative biopsies.23–25
A saturation biopsy is often defined as taking 20 or more cores, with some reports taking more than 70 cores.2,26
In this series a biopsy protocol (combination of MRI/US fusion guided biopsy and 12-core TRUS) averaged 17.8 cores and detected cancer in 54.4% (55 of 101) of trial patients.
Statistically significant associations existed between the degree of suspicion on MRI and cancer detected on fusion biopsy for patients and lesions (p <0.0001). When stratified by cancer suspicion on MRI, fusion biopsy detected cancer in 27.9%, 66.7% and 89.5% of patients with low, moderate and high suspicion, respectively. Cancer detection has traditionally been assessed by patient. However, with the development of targeted biopsy techniques and the exploration of focal therapy, cancer detection may be better assessed by lesion or biopsy core. In this study MRI/US fusion guided biopsy vs standard 12-core TRUS biopsy alone detected more cancer per core for all suspicion levels.
These findings emphasize the potential value of MRI/US fusion guided biopsy. This platform allows for the detection of cancer on high resolution imaging, the stratification of patients and lesions by cancer suspicion, and the ability to detect cancer at a higher rate per core than conventional random biopsy. These are all potential benefits that are not available with current biopsy techniques. Further research is warranted to develop recommendations for or against the use of MRI/US fusion biopsy alone or in addition to a standard 12-core TRUS biopsy.
The technique of MRI in guiding prostate biopsies continues to evolve.12,14,27
Hambrock et al recently reported a cancer detection rate of 59% in a series of 68 patients who underwent in-gantry MRI guided biopsy.13
The authors focused on a population with a median PSA of 13 ng/ml (range 4 to 243), of which 97.2% had a negative DRE. A similar overall detection rate of 55.4% was seen in this current trial in a patient population with a median PSA of 5.8 ng/ml (range 0.2 to 103), of which 90.1% had a negative DRE. This platform may be an alternative to MRI guided biopsies, allowing for office based biopsies. Positive biopsy rates in any study will be highly influenced by the patient selection bias inherent to practice patterns and screening or study population.
This platform may benefit patients enrolled in active surveillance or focal therapy protocols. Patients on active surveillance could be followed by prostate MRI. If new lesions were identified or suspicion of a previous lesion increased, MRI/US fusion could be used to target specific areas at risk. This platform tracks the locations of lesions as well as the trajectory and path of needle biopsies digitally, allowing prior targets to be sampled and monitored. MRI/US fusion guided imaging with EM tracking may also have a role in focal therapy for prostate cancer. This platform could be modified to incorporate focal therapies such as cryotherapy, high intensity focused ultrasound ablation or brachytherapy to provide image guidance and EM tracking of therapeutic instruments.
This study has several limitations. Without the evaluation of whole mount prostatectomy specimens the difference in accuracy between MRI/US fusion guided and 12-core standard TRUS cannot be determined. Furthermore, whether cancer was missed on initial MRI vs MRI/US fusion guided biopsy cannot be assessed. MRI is currently limited to identifying cancers greater than 3 mm. For lesions greater than 3 mm a previous histopathological correlation of peripheral tumors with multiparametric MRI showed sensitivities of 94%, 56% and 39%, and specificities of 83%, 96% and 98% for T2-weighted, dynamic contrast enhanced and spectroscopy, respectively.21
In a phantom, non-living model the mean spatial accuracy of this MRI/US fusion biopsy platform was 2.4 mm.20
This work demonstrated that this platform has the ability to guide biopsy needles to selected targets within an adequate margin of error. Only histopathological correlations will allow us to address these limitations conclusively. Despite these limitations cancer was detected at a higher rate than previously reported for other biopsy techniques, although overall rates are highly dependent upon the patient population.
Of the 55 patients in whom prostate cancer was found 10 had detection on 12-core TRUS biopsy alone, 10 on MRI/US fusion guided biopsy alone and 35 with both methods. Of the 10 patients with disease detected on 12-core TRUS biopsy alone 5, 4 and 1 had low, moderate and high suspicion of prostate cancer on MRI, respectively. Of the 10 patients with cancer detected on MRI/US fusion guided biopsy alone 3, 3 and 4 had low, moderate and high suspicion on MRI, respectively. Of the 35 patients with disease detected using either biopsy strategy 3, 19 and 12 had low, moderate and high suspicion on MRI, respectively. Thus, MRI/US fusion biopsy may aid in the detection of higher risk prostate disease compared to standard TRUS biopsy alone. However, further research is necessary to suggest why patients had disease detected on MRI/US fusion alone or TRUS biopsy alone.