A central problem in imaging biopsy procedures to detect prostate cancer is how to balance the requirement to detect tumor cells scattered throughout the prostate gland against the invasiveness of the method. Biopsy is conducted by a needle inserted into the prostate, and then when the needle is withdrawn, cells of the prostate come with it for analysis by histology. Ultrasound imaging is required to assist in correct placement of the needle into the prostate. Traditional ultrasound is not sufficiently accurate in its ability to discriminate between cancerous and non-cancerous tissue, so creative methods have been developed. Previous approaches used a biopsy needle inserted randomly into the prostate, typically in twelve different locations, with guidance by a transrectal ultrasound probe to enable the radiologist to visualize the prostate. The goal of this method was to successfully collect informative cores without overly traumatizing the gland with too many needle punctures, with associated bleeding, pain, infection and potential complications in healing. Because in many cases, malignant cells are ‘oligoclonal’, or scattered in islands throughout the prostate, the twelve cores method also relies somewhat on luck. One or more of the needle cores should contain tumor cells if the patient has clinically significant prostate cancer. It is also critical to balance any approach against over-diagnosing clinically insignificant cancer.
Newer methods now make use of images collected by MRI beforehand, where the suspicious islands in the gland are annotated on a computer screen, then fused with ultrasound images taken in real time, to guide placement of the biopsy needle. These ‘fusion biopsy’ approaches are intended to improve accuracy of sample collection and reduce trauma to the prostate. However, this newer method has not yet been universally adopted, and clinical trials are ongoing to establish whether the approach is superior to the twelve random cores. A key outcome measure to test the utility of the new method includes proportions of men with an accurate diagnosis of clinically significant prostate cancer. An important clinical trial in 2018 (Mortezavi et al; PMID: 29474846) of 415 men who presented for prostate biopsy found that the systemic twelve core approach outperformed fusion biopsy, because 58 cases (19.9%) of clinically significant prostate cancer would have been missed if only the fusion guided biopsy had been performed. New methods do not always mean better methods. Therefore, clinical trials continue to be conducted and the techniques are actively being refined.
An important recent report (February 2021) asked the question again in a group of 453 men who presented for prostate cancer biopsy at five centers in Canada (Klotz et al; PMID: 33538782). None of the men had a previous biopsy. In addition, the subjects were serum PSA level of 20 ng/mL or less. The subjects were randomized into two groups, to compare MRI-targeted biopsy alone against the systemic twelve cores approach. The main conclusion of the study was that the two approaches were clinically equal, and fusion biopsy was not inferior to systemic biopsy. Indeed, the MRI patients had 25% fewer adverse events (including prostatitis, bleeding, incontinence, hospital admissions, infections). The authors considered some of the potential factors that account for differences between methods, as well as among the five centers where the study was conducted. They noted that familiarity with the instrumentation and training could make a difference in outcomes, even though experienced radiologists and urologists were involved in every center. It is also possible that some of the patients will develop clinically significant cancer in the next few years, that might have been missed in this study, which could change the calculations. Overall, refinement of the fusion technique and wider usage and training seem likely to favor this innovation over the traditional twelve core, systematic approach, because the complication risks are more acceptable.