The ongoing lack of consensus regarding widespread PSA screening for prostate cancer (PCa) underscores the need for a better diagnostic pathway. PSA screening has saved countless lives, but it carries a two-edged sword:
- Clinically insignificant PCa that may not need immediate or even long-term treatment has been overdetected, leading to overtreatment with urinary and sexual side effects;
- Clinically significant PCa has been either under-diagnosed or altogether missed, leading to the eventual development of incurable metastatic prostate cancer in such patients.
There continues to be a role for PSA screening, but a growing body of research into the ability of mpMRI to deliver accurate images of PCa tumors is shifting the PCa diagnostic paradigm. Because mpMRI is shown to have high sensitivity especially in detecting significant (Gleason 7) lesions, it opens up the possibility of real time image-guided targeted biopsies. This is a dramatic improvement over transrectal ultrasound (TRUS) guided biopsies which are essentially blind and random. They are blind because ultrasound does not discriminate cancerous tissue from noncancerous tissue within the gland; they are random due to a conceptual division of a prostate gland into 12 or more segments (half on each side) into which needles are directed in a hit-or-miss attempt to capture cancerous tissue. Numerous studies of RP patients have demonstrated inadequate correspondence between biopsy results vs. the actual size, shape, location and grade of the RP specimens. Thus, confidence in TRUS biopsy is diminished.
Ghai & Trachtenberg (2015) offer a review of the current state of targeted prostate biopsies done in real time with the patient lying within the MRI.[i] They cite published evidence that MRI-targeted biopsy has a higher overall rate than TRUS biopsy at detecting significant PCa (requires treatment quickly) and a lower overall detection rate of insignificant PCa (may not require treatment quickly). As early as 2000, biopsies under MRI guidance were done in an open magnet that permitted prostate access through the perineum (skin behind the scrotum); however, open magnets at that time were not powerful enough to deliver today’s high-resolution images. Since 2005, several papers have presented results of prostate biopsies conducted using MR-compatible biopsy equipment and 1.5 Tesla or 3 Tesla magnets, most done transrectally with the patient in a prone position. While successful detection rates range from 8% to 70%, the authors highlight the largest published series on in-bore prostate biopsy (Hoeks et al. 2012) in which “…265 patients with PSA over 4.0 ng/mL and at least one previous negative TRUS biopsy were sampled following mp-MRI in a 3T magnet. Cancer was detected in 33% of the sites called on MRI, and 87% of these were clinically significant.” In addition, clinical studies are ongoing into other patient positioning, transperineal vs. transrectal approaches, and MR-compatible robotic-assisted biopsy devices. Two downsides to MRI guidance have been raised:
- Longer procedure time as the patient may need to be moved in and out of the magnet to recalibrate and move the needle guide to hit the correct location and number of targets. However, experts agree that the accuracy of the diagnosis while minimizing the number of needles offers a greater benefit for patient comfort and treatment planning.
- MRI in radiology imaging centers is expensive compared to in-office ultrasound equipment. This concern is countered by de Rooijet al. (2014) who found the long-term costs roughly equivalent. They compared quality of life (QoL) and health care costs for TRUS biopsy vs. MRI targeted biopsy, using an analytic model that included “… the cascading effects for a period of 10 years following initial referral for biopsy. Their results suggested comparable healthcare costs in the two strategies but an improved QoL in the imaging arm. The benefit in QoL is derived from decrease in overdiagnosis and overtreatment in the imaging arm.”
Ghai & Trachtenberg conclude that the advantages of MRI-targeted biopsy “… include the potential of performing less number of biopsies, based on the negative predictive value of mp-MRI, and therefore decreasing the incidence of complications from biopsies (multiresistant sepsis), increased sampling efficiency, decreased histopathology costs, better characterization of Gleason grade and fewer missed clinically significant cancers.”
Research published in early 2015 out of Italy bears out the above review article. Panebianco et al. designed a study to determine whether in-bore MRI targeted biopsy could improve diagnostic performance in patients with suspicion of PCa.[ii] Their study cohort was composed of 23 patients whose 1.5 T mpMRI scans identified a total of 26 suspicious regions. They underwent in-bore targeted biopsies. Total procedure time ranged from 35-55 minutes (mean 40 minutes). The authors observe that the procedure was well-tolerated by all men, and no major complications were observed. They report, “The detection rate for the diagnosis of PCa was 80, and 90 % of detected PCa were of intermediate aggressiveness.”
The Summer 2015 issue of PAACT’s patient magazine, Prostate Cancer Communication, has an article by Robert Princenthal, MD.[iii] (NOTE: This magazine has previously carried two articles by Dr. Sperling[iv]). Dr. Rosenthal offers an articulate summary of how MRI-targeted biopsy offers key advantages: improved aggression assessment, risk reduction through fewer needles, better treatment decision-making and planning. He writes:
Prostate cancer is a tale of two diseases. Many men with prostate cancer have low-risk, indolent tumors that are unlikely to grow or cause harm for many years, if ever. Other men have high-risk tumors that can quickly become lethal if they are not detected and treated as early as possible. Because the combination of PSA testing and TRUS biopsy provides incomplete assessment of the prostate gland, many men with low-risk, indolent disease elect to receive radical treatment that could be more harmful than it is beneficial. Numerous men unnecessarily suffer from complications like impotence and incontinence, even with the introduction of robotic prostatectomy.
[ii] Panebianco V, Barchetti F, Manenti G et al. MR imaging-guided prostate biopsy: Technical features and preliminary results. Radiol Med. 2015 Jan 13. Epub ahead of print. doi: 10.1007/s11547-014-0490-0
[iii] Princenthal, R. Adding multiparametric MRI to prostate cancer screening will save lives and money. Prostate Cancer Communication (PAACT, Grand Rapids, MI); Summer 2015:3-7
[iv] Sperling, D. Focal laser ablation of prostate tumors. Prostate Cancer Communication (PAACT, Grand Rapids, MI); Dec 2012:14-17; and Focal laser ablation: an update; Winter 2014:20-22.