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Prostate cancer: is inapparent tumor at endorectal MR and MR spectroscopic imaging a favorable prognostic finding in patients who select active surveillance?
Cabrera AR, Coakley FV, Westphalen AC, Lu Y, Zhao S, Shinohara K, Carroll PR, Kurhanewicz J
Department of Radiology, University of California, San Francisco, CA, USA
Radiology. 2008; 247: 444-50

• Purpose: To retrospectively determine whether inapparent tumor at endorectal magnetic resonance (MR) imaging and MR spectroscopic imaging is a favorable prognostic finding in prostate cancer patients who select active surveillance for management.
• Materials and Methods: Committee on Human Research approval was obtained and compliance with HIPAA regulations was observed, with waiver of requirement for written consent. Ninety-two men (mean age, 64 years; range, 43-85 years) were retrospectively identified who had biopsy-proved prostate cancer, who had undergone baseline endorectal MR imaging and MR spectroscopic imaging, and who had selected active surveillance for management. Their mean baseline serum prostate-specific antigen (PSA) level was 5.5 ng/mL, and the median Gleason score was 6. Two readers with 10 and 3 years of experience independently reviewed all MR images and determined whether tumor was apparent on the basis of evaluation of established morphologic and metabolic findings. Another investigator compiled data about baseline clinical stage, biopsy findings, and serum PSA measurements. Multiple logistic regression analysis was used to investigate the relationship between the clinical parameters and tumor apparency at MR imaging and the biochemical outcome.
• Results: At baseline MR imaging, readers 1 and 2 considered 54 and 26 patients, respectively, to have inapparent tumor (fair interobserver agreement; kappa = 0.30). During a mean follow-up of 4.8 years, 52 patients had a stable PSA level and 40 had an increasing PSA level. In multivariate analysis, no significant association was found between the baseline clinical stage, Gleason score, serum PSA level, or the presence of apparent tumor at endorectal MR imaging and MR spectroscopic imaging for either reader and the biochemical outcome (P > .05 for all).
• Conclusion: Endorectal MR imaging and MR spectroscopic imaging findings of tumor apparency or inapparency in prostate cancer patients who select active surveillance for management do not appear to be of prognostic value. (c) RSNA, 2008.
  
  
• Editorial Comment
  Endorectal MR imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) is emerging as a useful technique for detection and local evaluation of prostate cancer extent and aggressiveness. Combined MRI/MRSI has shown excellent sensitivity and specificity for detecting cancer in the peripheral zone. These techniques are also capable of detecting tumor in the transition zone and may reduce the rate of false-negative biopsies and hence decrease the need for more extensive biopsy protocols and multiple repeat biopsy procedures. The authors of this retrospective study show that tumor apparency or inapparency on MRI/MRSI has no predictive value in the active-surveillance population. In other words, in patients with-low risk prostate cancer, tumor apparency or inapparency on baseline imaging studies are not helpful in predicting disease progression. Patients with negative MRI+MRSI examinations were just as likely to develop an increasing PSA level (progression of disease) as those with radiologically apparent tumors. We agree with the authors’ statement that the results of this study do not undermine the role of MRI/MRSI in the evaluation of prostate cancer. In a previous study using extended prostate biopsy (12 cores) as a reference, MRI/MRSI showed a negative predictive value of 100% for the detection of prostate cancer (1). In our small sample, all patients with tumor inapparency on MRI/MRSI had negative extended biopsy. Since published data from the Prostate Cancer Prevention Trial demonstrated that there is no PSA level below which the risk of having prostate cancer is zero, probably the same is happening with currently available armamentarium used to predict its progression. As shown in this study PSA levels and Gleason scores, similar to MRI/MRSI, are of limited value in predicting disease progression. For this purpose, probably we will need a new and more specific biologic marker.

Reference

Prando A, Kurhanewicz J, Borges AP, Oliveira EM Jr, Figueiredo E: Prostatic biopsy directed with endorectal MR spectroscopic imaging findings in patients with elevated prostate specific antigen levels and prior negative biopsy findings: early experience. Radiology. 2005; 236: 903-10.

Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging, Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: adilson.prando@gmail.com