Evaluation of Transperineal Template Biopsy as a Means of Guiding Targeted Cryotherapy for Localized Prostate Cancer
The advent of early detection and screening programs based on prostate specific antigen (PSA) has resulted in a dramatic increase in the number of men who undergo transrectal biopsy of the prostate to diagnose or exclude malignancy. Unfortunately, despite modifications to the standard sampling schema, false negative rates associated with transrectal biopsy remain unacceptably high. As a result, urologists are frequently faced with the diagnostic challenge of what to do with men who remain by clinical criteria at high risk for prostate caner (i.e. elevated PSA, short PSA doubling time, etc.) but have negative results on transrectal biopsy.
To address the issue of high false negative rates associated with standard transrectal methods, Dr. Todd Igel (Chair – Department of Urology, Mayo Clinic Jacksonville) developed a novel transperineal ultrasound-guided template biopsy technique for use in high-risk men with previously negative results on transrectal biopsy (see Figures 1 and 2). Details of the actual procedure and rates of tumor detection in high risk men can be found in a recently published update manuscript (Pinkstaff D, et al. Journal of Urology, 2005).
In addition to several other advantages over standard transrectal biopsy methods, this template technique allows for systematic partitioning of the prostate as well as accurate and reproducible probe placement. This advantage begs the question of whether this method could be used as a guide for targeted, interstitial therapies designed to ablate tumor but preserve normal prostatic tissue (i.e. cryoablation and brachytherapy). Indeed, the template we use for the biopsy procedure is the very same one that is used for the placement of the freezing probes during cryotherapy and the seeds during brachytherapy. Without question, more and more patients are interested in exploring targeted therapies that maintain a high degree of efficacy but have lowered associated morbidities than surgery. Authors of a recent review article touting the impressive efficacy of cryoablation stated that “the potential for cryoablation and other targeted therapies to be applied focally may become significant if and when diagnostic tests become advanced enough to predict and localize foci of cancer”. As such, there is a clear need to evaluate the ability of our transperineal template biopsy technique to accurately localize tumors in the prostate and moreover, to explore the possibility of using it as a means for guiding targeted, tissue-sparing procedures.
In this project we will compare transperineal template biopsy results with whole mount prostate sections from the same individual. The concept in this project is that transperineal ultrasound-guided template biopsy provides a method of accurately localizing prostate cancer in high-risk men who undergo radical prostatectomy. Moreover, the accuracy associated with our transperineal template biopsy is high enough that knowledge of tumor location obtained using this method can be used to successfully direct targeted, interstitial therapy (cryotherapy) in these high-risk men. Explicitly, we expect that our template biopsy method will have a high degree of agreement with regard to the number and location of unique tumor foci in the prostate when compared to the “gold standard” analysis of whole mount sections. In addition, we expect that simulated cryotherapy based on knowledge of tumor location obtained from our template biopsy will result in eradication of clinically significant cancer in >80% of men studied.