By: Dan Sperling, MD

A recent study published by a Korean research team reported on the ability of multiparametric MRI (mpMRI) to confirm prostate cancer recurrence in the prostate bed following radical prostatectomy.[i] The performance of the imaging was evaluated by comparing various combinations of parameters to find the optimal detection ability of 3T mpMRI.

About recurrence

When the cancer is contained in the prostate gland at the time of surgery, it is expected that surgical removal will result in post-treatment PSA blood tests showing a value of zero, because it is assumed that no prostate tissue (cancerous or normal) was left behind. Therefore, recurrence (the return of cancer) is suspected when a post-treatment PSA blood test reveals a value greater than 0.2 ng/mL. If subsequent blood tests show a gradual rise in PSA over time, this is called biochemical recurrence (BCR) because in such cases, PSA is a biomarker for prostate cancer that had escaped the treatment and is now starting to grow into one or more tumors.

Rates of biochemical recurrence vary, and are often associated with a positive surgical margin (PSM), especially in cases of intermediate-to-high risk disease using the d’Amico risk stratification. In one single-surgeon study of 439 cases, at 2 years after robotic prostatectomy, 12% had suspicion of BCR compared with 6% whose surgical margins were disease-free.[ii] A larger study involving 1159 robotic-assisted prostatectomy patients revealed an overall rate of BCR suspicion of 28% at five years after treatment, and noted that negative surgical margins were correlated with lower BCR rates for low- and intermediate-risk groups. However, multifocal and longer PSM were “associated with higher biochemical recurrence rates compared with unifocal and shorter positive margins.”[iii]

It is crucial to identify the location of BCR in terms of clinical strategy going forward. For example, if it is established with reasonable confidence that the new cancer growth is in the prostate bed, or tissue surrounding the area where the gland was removed, radiation therapy to the area may be a good choice for salvage treatment. On the other hand, evidence that the cancer has spread regionally into the pelvic lymph nodes or pelvic bones, or remotely to distant organs, will indicate the need for a systemic treatment, usually hormone therapy to block testosterone production.

mpMRI’s ability to identify recurrence

Returning to the Korean study, the authors’ objective was to assess the utility of mpMRI in identifying tumor growth in the soft tissues adjacent to the prostate removal. They analyzed the cases of 43 men with rising PSA following radical prostatectomy who underwent 3T mpMRI; the parameters used were T2 weighted imaging (T2 MRI), diffusion weighted imaging (DWI) and dynamic contrast enhanced MRI (DCE-MRI). NOTE: T2 MRI is standard imaging that registers tissue differences. Go to https://sperlingprostatecenter.com/mri-imaging-prostate-cancer-two-parameters/ for a more detailed explanation of DWI and DCE.

The Korean study employed very high quality, state-of-the-art imaging using three parameters. All the patients had a suspected soft tissue tumor growth in the prostate bed, and all patients were put through a TRUS biopsy. In addition, the researchers enrolled 14 BCR-free patients as a control group. Two experienced radiologists, independently of each other, read and analyzed four different imaging datasets (all the mpMRI parameters in different combinations).

Not surprisingly, integrating T2, DWI and DCE produced the best imaging results, which were also correlated with the biopsy results. The authors concluded, “DCE-MRI or DWI in combination with T2WI at 3T with a phased-array coil appears to be more useful than T2WI alone in evaluating suspected soft tissue lesion of the prostate bed after RP.” This bears out an earlier study on combined parameters being better than T2 weighted images alone, which is described at https://sperlingprostatecenter.com/combining-mri-parameters-better-t2-weighting-alone/.

Thus, the combined use of multiple parameters, in this case T2 MRI, DWI, and DCE-MRI can be of great clinical value in helping plan clinical strategy for biochemical recurrence in the prostate bed following surgery.

[i] Cha D, Kim CK, Park SY  et al. Evaluation of suspected soft tissue lesion in the prostate bed after radical prostatectomy using 3T multiparametric magnetic resonance imaging. Magn Reson Imaging. 2014 Dec 16. pii: S0730-725X(14)00357-9.

[ii]Tanimoto R, Fashola Y, Scotland KB et al. Risk factors for biochemical recurrence after robotic assisted radical prostatectomy: a single surgeon experience. BMC Urol. 2015 Apr 8;15(1):27.

[iii] Ginzburg S, Nevers T, Staff I et al. Prostate cancer biochemical recurrence rates after robotic-assisted laparoscopic radical prostatectomy. JSLS. 2012 Jul-Sep;16(3):443-50.