Accuracy of DCE MRI in men with locally recurrent prostate cancer

According to a media release issued last Friday, “A pelvic MRI scan with IV contrast and rectal balloon is highly effective in identifying local recurrence even at low PSA values in prostate cancer patients with a rising or persistently elevated PSA after prostatectomy.”

The media release refers to data presented by Choi et al. at the Cancer Imaging and Radiation Therapy Symposium in Atlanta, GA.

Choi and his colleagues reviewed data from patients treated with salvage radiation therapy between January of 2004 and October of 2010 at the M. D. Anderson Cancer Center. All such patients had prostate cancer recurrence after prior first-line treatment with radical prostatectomy. Of the 389 post-prostatectomy patients treated, 143 were given dynamic contrast-enhanced endorectal magnetic resonance imaging (DCE MRI) of the pelvis before starting their salvage treatment. A focal area of enhancement with contrast in the prostate/seminal vesicle fossa was defined as being suspicious for local recurrence when observed on DCE MRI.

The study results are as follows:

  • The median PSA at the time of the DCE MRI scan was 0.3 ng/ml (range, 0.1 to 8.0 ng/ml).
  • 35/143 patients (24.5 percent) had DCE MRI findings suspicious for a local recurrence.
  • 26/35 patients were given a transrectal ultrasound-guided biopsy of the prostate/seminal vesicle fossa.
    • 23/26 patients (88.5 percent) who received a biopsy had pathologically proven local recurrence.
    • 1/26 patients had residual non-cancerous prostate tissue seen on pathology.
  • Of the 9 patients with suspicious DCE MRI findings treated with salvage radiation without pathologic confirmation of the suspicious MRI result
    • 8 patients remain disease free after a median follow-up of 22 months (range, 5 to 63 months).
    • 7/8 patients had a PSA level < 0.1 ng/ml.
    • 1/8 patients had a PSA level of 0.1 ng/ml.
  • The median PSA value for patients with a biopsy-proven local recurrence was 1.35 ng/ml (range, 0.3 to 8.0 ng/ml).
  • 8/23 patients with a biopsy-proven recurrence had a PSA less than 1.0 ng/ml at the time of their biopsy.
  • 9 patients with no suspicious findings on DCE MRI were also given prostate/seminal vesicle fossa biopsies.
    • 1/9 patients had a pathologically proven local recurrence.
    • The negative predictive value (NPV) of DCE MRI was 88.9 percent.

Choi et al. conclude that DCE MRI of the pelvis can be used effectively to identify local recurrence of prostate cancer after prostatectomy —  in patients with PSA values as low as 0.3 ng/ml.

Now we are getting better at the identification of locally recurrent cancerous tissue in some men with a rising PSA after first-line therapy. However, some aspects of this study seem very puzzling to us.

According to slides shown at the press conference where these data were presented, 113/143 men given a DCE MRI had an undetectable PSA (defined as being <0.1 ng/ml) after surgery, and only 30/143 patients had a detectable PSA (with a median PSA of 0.2 ng/ml and a range of 0.1 -1.7 ng/ml). To claim that the negative predictive value of DCE MRI is 88.9 percent on the basis of these data seems odd at best. It might be reasonable to claim that DCE MRI had an NPV of 88.9 percent in men with a rising PSA of ≥ 0.3 ng/ml if a TRUS-guided biopsy of the prostate fossa was given to all men with a PSA level of 0.3 ng/ml or higher, but it is not clear that this is what was actually done.

The other thing that is not clear at all is why 113 men with a PSA of < 0.1 ng/ml were being characterized as having recurrent prostate cancer and being given a DCE MRI in the first place. Were these men with high Gleason scores and/or high PSA levels prior to their surgery and therefore in whom very small rises in the PSA level post-surgery were likely to be indicative of progressive disease? Biochemical recurrence after surgery normally requires the PSA to rise to a level of 0.2 ng/ml, but it is well known that some men may be appropriately treated with salvage radiation before a rising PSA reaches that level if they were originally though to be at high risk for progression. But then if they are at high risk for progression, is that progression likely to be local?

Without seeing a great deal more detail about the patients actually being given DCE MRI in this retrospective analysis, we are uncertain of exactly what conclusions can be drawn from this study.

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