Multiparametric pelvic magnetic resonance imaging (mpMRI) can improve predictions of salvage radiotherapy (sXRT) outcomes following radical prostatectomy, according to a new study.

For patients with pre-sXRT PSA levels of 0.5 ng/mL or less, negative mpMRI findings independently predict an increased likelihood of PSA recurrence and metastasis after sXRT.

The study, by a team at Mayo Clinic in Rochester, Minnesota, led by R. Jeffrey Karnes, MD, included 473 sXRT patients who were evaluated by pelvic mpMRI after experiencing biochemical recurrence of prostate cancer following RP. Of these patients, 204 (57%) had lesions on mpMRI. After excluding nodal/bone lesions, 29% of patients had PSA recurrence and 14% had metastasis at a median follow-up of 45 months after salvage radiation, the investigators reported online ahead of print in European Urology.

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Among patients with a pre-salvage PSA of 0.5 ng/mL or less, PSA recurrence and metastasis were significantly more likely to occur among patients with a negative than positive mpMRI (39% vs 12% and 16% vs 2%, respectively) at 4 years after sXRT, Dr Karnes’ group reported. In addition, among patients with a PSA of 0.5 ng/mL or less, the addition of mpMRI to a propensity score created using variables from the original Stephenson nomogram improved the c-statistic from 0.71 to 0.77 for PSA recurrence and from 0.66 to 0.77 for metastasis. For patients with a pre-salvage PSA level above 5 ng/mL, mpMRI did not predict PSA recurrence or metastasis.

The investigators state that the findings validate their hypothesis that a negative mpMRI in the context of rising post-RP PSA indicates an increased likelihood of a distant source of that PSA. Although patients with a negative mpMRI had slightly lower pre-salvage PSA compared with patients who had a positive mpMRI, they had a slightly shorter PSA doubling time (9.4 vs 11.1 months), “which supports the hypothesis that there is a higher risk of occult micrometastatic disease for MRI-negative patients.”

Dr Karnes and his colleagues concluded that pre-sXRT mpMRI “is a valuable adjunct to current clinicopathologic variables used to estimate the success of sXRT.”

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Sharma V, Nehra A, Colicchia M, et al. Multiparametric resonance imaging is an independent predictor of salvage radiotherapy outcomes after radical prostatectomy. Eur Urol 2017; published online ahead of print.