EURURO Vol. 72 No. 6

Letter to the Editor

Re: Sungmin Woo, Chong Hyun Suh, Sang Youn Kim,

Jeong Yeon Cho, Seung Hyup Kim. Diagnostic

Performance of Magnetic Resonance Imaging for

the Detection of Bone Metastasis in Prostate Cancer:

A Systematic Review and Meta-analysis. Eur Urol.

In press.

http://dx.doi.org/10.1016/j.eururo.2017.03.042

Woo et al

[1]

have presented a remarkable systematic

review with meta-analysis on the potential role of

magnetic resonance imaging (MRI) in detecting bone

metastasis in prostate cancer patients. They suggest that

MRI is a necessary work-up modality for screening and

monitoring purposes. Although they report that MRI has

high accuracy in detecting bone metastasis, this does not

directly devalue the current role of bone scans. To date,

there is no evidence from randomized controlled trials

evaluating the accuracy of MRI, bone scans, computed

tomography (CT), positron emission tomography (PET)

CT, and single-photon emission CT (SPECT)

[2]

. The

current evidence on the accuracy of each modality has

been derived from retrospective studies, which can have a

possible bias towards blinding for interpreters. Moreover,

there is no metastatic prostate cancer–related reference

standard in most studies, which could bias results. Hence,

although the authors used the QUADAS-2 tool to describe

methodological bias, assessment of methodological bias

should be more rigorous. In addition, considering the high

prevalence of bone metastasis in the studies included, the

statistical uncertainty arising from studying a relatively

small number of patients without metastasis can lead to

inaccurate estimates of specificity. Furthermore, clarifi-

cation is also required regarding: (1) the time gap

between performance of the reference standard and

MRI; (2) whether radiologists carried out interpretation

without knowledge not only of the reference standard but

also prior clinical information including clinical staging

and prostate-specific antigen (PSA); and (3) whether the

reference standard was also interpreted without the MRI

results. In other words, pooled estimates of sensitivity

and specificity could be biased since the results for the

MRI or reference standard could be a kind of series

of tests with prior information. To compare the result

for a bone scan, it should have been assessed via

conditional sensitivity and specificity, not via a single-

test design

[3]

The expected role of MRI also has to be clearly described.

The review includes both initial work-up for patients and

monitoring of treated patients, which contributes to the

heterogeneity. Since the authors have shown the impact of

including different groups together based on the sensitivity

analysis, these are totally different clinical settings from a

clinical oncologic view. In detecting vertebral bone

metastasis, MRI had superior accuracy to bone scans in

terms of sensitivity; however, it had similar accuracy in

terms of specificity

[2] .

Liu et al

[2]

recently presented a

meta-analysis comparing the diagnostic accuracy of MRI,

CT, PET, bone scans, and SPECT for vertebral metastases

[2]

. Their analysis of accuracy after categorization in a

patient setting and in a lesion setting was not included in

the current study.

Finally, the study did not include any results using

quantitative data, which could be available in multi-

parametric MRI settings. There are emerging studies

showing that the sensitivity of MRI is superior to that of

bone scans

[4,5] ;

however, in real clinical settings, PSA and

Gleason score play important screening roles in predicting

clinical stage. Hence, specificity could be more important in

the initial work-up, while sensitivity could be more

important in monitoring. Taking the results of this study

together with those from other studies, MRI might have a

positive role in a monitoring setting, but more evidence is

needed for initial work-up.

Conflicts of interest:

The authors have nothing to disclose.

Acknowledgments:

This study was supported by Soonchunhyang

University Research Fund. The sponsor played a role in manuscript

preparation.

References

[1] Woo S, Suh CH, Kim SY, Cho JY, Kim SH. Diagnostic performance of

magnetic resonance imaging for the detection of bone metastasis in

prostate cancer: a systematic review and meta-analysis. Eur Urol.

In press.

http://dx.doi.org/10.1016/j.eururo.2017.03.042

E U R O P E A N U R O L O G Y 7 2 ( 2 0 1 7 ) e 1 6 4 – e 1 6 5

available at

www.scienced irect.com

journal homepage:

www.europeanurology.com

DOI of original article:

http://dx.doi.org/10.1016/j.eururo.2017.03.042

http://dx.doi.org/10.1016/j.eururo.2017.06.024

0302-2838/