Perspectives in Urology
Prebiopsy magnetic resonance studies for prostate cancer diagnosis
Article first published online: 23 OCT 2012
© 2012 The Japanese Urological Association
International Journal of Urology
Volume 20, Issue 2, pages 140–141, February 2013
How to Cite
Kumar, R. and Jagannathan, N. R. (2013), Prebiopsy magnetic resonance studies for prostate cancer diagnosis. International Journal of Urology, 20: 140–141. doi: 10.1111/j.1442-2042.2012.03201.x
- Issue published online: 1 FEB 2013
- Article first published online: 23 OCT 2012
- Manuscript Accepted: 19 SEP 2012
- Manuscript Received: 12 JUL 2012
The inaccuracy of prostate-specific antigen (PSA) in detecting prostate cancer is a major clinical challenge. More than 70% men with PSA below 10 ng/mL will have a negative prostate biopsy. Apart from the cost, discomfort and potential complications, negative biopsies in the presence of an abnormal PSA result in continued concern about harboring cancer. Improving the positive predictive value and specificity of investigational procedures is thus an area of active research.
Magnetic resonance (MR)-based methods have the unique ability to assess anatomical, functional and biochemical properties of tissues non-invasively. These include anatomic MR imaging and functional technologies, such as MR spectroscopy imaging (MRSI), diffusion weighted imaging and dynamic contrast enhanced MR imaging. Although anatomical imaging suffers from a lack of sensitivity and specificity in diagnosing prostate cancer, combined anatomical and functional MR methods might help select a subgroup of patients for whom biopsies can be avoided. In addition, they might identify abnormal areas that can be specifically targeted during biopsy, and thus decrease the number of biopsies and improve overall yield.
Functional MR identifies molecular and biochemical signatures of tissues. Parameters from functional MR methods, especially MRS, might be helpful in detecting early changes of disease before the appearance of morphological or secretory changes. In prostate cancer, this would mean that MR detectable changes might occur before the level of PSA rises or biopsy detectable tumor. Furthermore, as MR directly investigates the tissue, it is likely to be more disease specific than surrogate markers, such as PSA, which are organ specific but not pathology specific. In essence, MRS resembles an in vivo biochemical biopsy. We believe this hypothesis is central to understanding the results achieved on MR studies of the prostate.
Our experience of investigating prebiopsy MR methods for prostate cancer detection since 1999 has shown that MRSI can reliably identify abnormal voxels and guide biopsies. Our results showed an increased yield on such targeted biopsies and a high negative predictive value for MRSI. We also noticed that MRSI positivity rates resembled autopsy reported rates of prostate cancer, higher than biopsy detected cancers.
MR might not be considered a screening test at this point of time and cost analysis studies are required. However, adding MR studies before biopsies in men with elevated PSA might improve specificity and overcome some of the problems associated with PSA-screened prostate cancer detection. Based on our experience, we suggest a revised algorithm for biopsies that might increase the yield of significant cancers while reducing the number of patients requiring a biopsy and the number of biopsies per patient (Fig. 1). In addition, there is evidence that these targeted biopsies might more accurately predict the final grade of cancer than random biopsies, thus optimizing treatment plans. Results of other investigators who used different MR methods with similar outcomes lend credence to our hypothesis.[5, 6] Prebiopsy MR might significantly reduce the burden of biopsies currently being carried out because of high false positive rates of PSA.
There is thus a need to revisit the current protocols for initiating a prostate biopsy. Clearly the PSA alone is not enough. Adding prebiopsy MR studies might help solve a number of conundrums that currently surround PSA testing.
- 2Transrectal ultrasound-guided biopsy of prostate voxels identified as suspicious of malignancy on three-dimensional (1)H MR spectroscopic imaging in patients with abnormal digital rectal examination or raised prostate specific antigen level of 4–10 ng/ml. NMR Biomed. 2007; 20: 11–20., , et al.
- 6Role of magnetic resonance imaging before initial biopsy: comparison of magnetic resonance imaging-targeted and systematic biopsy for significant prostate cancer detection. BJU Int. 2011; 108 (8 Pt 2): E171–178., , et al.