Amongst a global trend from non-extended to extended prostate biopsy, no standard extended biopsy scheme has been established yet. In this well organized review article, the authors are addressing controversial issues in the diagnosis of prostate cancer with an updated literature review.1 Among all, Tables 6 and 7. How to use the information along with clinical information for precise risk assessment is the most critical point in the treatment decision-making process of prostate cancer. Some issues, however, should be addressed.
Ambiguity in the definition of saturation biopsy
My first concern is what the term saturation biopsy means. As was the case in the majority of previous literature, the authors adopted a somewhat arbitrary definition of saturation biopsy, a biopsy protocol in which 20 or more cores are taken in a systematic fashion. Unfortunately, there is ambiguity associated with this kind of definition. After the pioneering work by Stewart et al.,2 several investigators have reported the diagnostic performance of saturation biopsy protocols.3–7 However, saturation biopsy was defined as simply taking a larger number of cores in most reports and less attention has been paid on how to locate sampling sites within the gland effectively. For example, Jones and his co-workers reported that a transrectal 24-core biopsy did not improve cancer detection compared with a transrectal 10-core biopsy and suggested that extended transrectal biopsy beyond 10–12 cores does not appear to be appropriate at the initial biopsy.3 Pepe et al. demonstrated that transrectal 24–37 core biopsy offers no advantage over a transrectal 12-core biopsy at the initial biopsy setting.4 In the analysis of a large cohort including more than 3000 men, Scattoni and his co-workers revealed that a diagnostic advantage of a transrectal 18-core biopsy over a transrectal 12-core biopsy was seen only in men with a prostate larger than 55 mL.5 In contrast, Ravery et al. found that the cancer detection rate of a transrectal 20-core biopsy was significantly better than that of a transrectal 10-core biopsy.6 Although Guichard et al. showed the superiority of a transrectal 21-core biopsy over a transrectal 12-core biopsy, the reported increment of the cancer detection rate was no more than 9.8%.7 These studies illustrate that additional transrectal sampling to the conventional transrectal 12-core biopsy might not lead to a significant improvement in cancer detection.8 Altogether, these saturation biopsy strategies, taking a large number of cores through a single approach, seem neither efficient nor practical. A recent editorial entitled ‘Saturation biopsy of the prostate. Why saturation does not saturate’ addressed this issue very clearly and concluded that the term saturation biopsy would be rightfully used only when a biopsy protocol that associates maximized diagnostic yield is devised.9
Saturation of the cancer detection rate
From a practical point of view, the optimal extended biopsy scheme should yield a maximum cancer detection rate with a minimal number of biopsy cores.10,11 To this end, tissue sampling sites are to be located to cover the entire peripheral zone with special attention to the anterior portion.10–13 In principle, the more biopsy cores that are taken the more cancers would be detected by prostate biopsy. However, it should be noted that the relationship between the number of biopsy cores and the resultant cancer detection rate does not correlate linearly. Instead, the cancer detection rate would become saturated when increasing the number of biopsy cores.10,11,14
We analyzed the saturation phenomena in the cancer detection rate of extended prostate biopsy by using a 3-D 26-core systematic super-extended biopsy protocol.10,11 In these analyses, subset biopsy schemes were determined by recursive partitioning to achieve maximum a cancer detection rate at given number of biopsy cores through single transrectal, single transperineal or 3-D combination of transrectal and transperineal approaches. When cancer detection rates of biopsy schemes were plotted against the number of biopsy cores, saturation in the cancer detection rate was clearly demonstrated either in the initial (Fig. 1)10 or in the repeat biopsy setting (Fig. 2).11 To overcome the saturation in the cancer detection rate in single approach extended biopsies and to obtain a higher cancer detection rate with a given number of biopsy cores, a 3-D combination of transrectal and transperineal approaches has been shown advantageous either in the initial10 or in the repeat biopsy setting.11
We have successfully extracted a 3-D 14-core biopsy protocol that can detect 95% of cancers detected by the 3-D 26-core biopsy. According to the above-mentioned criteria defining saturation biopsy with an arbitrary cut-off core number of 20, the 3-D 26-core biopsy would be classified as a saturation biopsy but the 3-D 14-core subset biopsy would not, despite no larger than a 5% difference in the cancer detection rate.
Diffusion-weighted magnetic resonance imaging (MRI) for visualizing small prostate cancer
Non-invasive imaging study for pre-biopsy identification of cancerous lesions is long awaited. In this regard, diffusion-weighted MRI (DW-MRI) without a contrast agent has been explored as a fascinating modality.15 Although the authors successfully completed a comprehensive review on ultrasound and elastography, we could not find any description on the potential diagnostic power of DW-MRI in their article. Further comparison between ultrasound and DW-MRI is warranted.
As the authors mentioned in the article, there might be no controversy surrounding the notion that systematic tissue sampling is one of the most important concepts underlying contemporary prostate biopsy protocols. In addition to the systematic sampling sites in any given biopsy protocol, imaging study-based targeted tissue samplings might further improve the cancer detection rate.
A novel technique for local anesthesia for transperineal prostate biopsy
Readers of the Journal will find a detailed review on the important and indispensable roles of local anesthesia in transrectal biopsy in this article. I believe that it will provide a good perspective on the choice of the local anesthetic method for transrectal biopsy. Considering that both guidelines from The American Urological Association and The European Association of Urology recommend the transperineal approach as a useful alternative approach, how to perform transperineal biopsy under reliable local anesthesia is the next concern. To this end, I would like to supplement this article with a recent innovative report16 that appeared in this Journal, introducing a simple, effective and reproducible local anesthetic method for transperineal biopsy and consequently for 3-D biopsy.