Prostate MRI May Help Decide on Watchful Waiting (CME/CE)

Authors: MedPage Today

By Charles Bankhead, Staff Writer, MedPage Today
Published: September 26, 2012
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

MRI evaluation of clinically low-risk prostate cancer demonstrated high accuracy for predicting disease status in men evaluated for watchful waiting, data from a prospective clinical study showed.

A low imaging score by endorectal MRI had ≥95% negative predictive value and specificity for upgrading on biopsy. A high score correlated with upgrading in about 90% of cases. By multivariate analysis, a higher MRI score doubled the likelihood of upgrading on confirmatory biopsy.

Collectively, the findings support a role for MRI in the initial assessment of appropriateness for watchful waiting, or active surveillance, Hebert Alberto Vargas, MD, of Memorial Sloan-Kettering Cancer Center in New York City, and co-authors reported online in the Journal of Urology.

"The success of active surveillance as a management strategy for prostate cancer relies primarily on the accurate identification of patients with low-risk disease unlikely to progress," they concluded.

"The fact that clear tumor visualization on MRI was predictive of upgrading on confirmatory prostate biopsy suggests that prostate MRI may contribute to the complex process of assessing patient eligibility for active surveillance."

The downstaging of newly diagnosed prostate cancer in the era of PSA testing has led to concern about possible overtreatment. In response to the concern, interest in active surveillance has increased, as has its effectiveness, reflected in 3- to 10-year survival of 97% to 100%, the authors noted in their introduction.

The National Comprehensive Cancer Network has recommended active surveillance as sole initial therapy for patients with low-risk prostate cancer and a life expectancy of at least 10 years or with very low-risk disease and life expectancy of 20 years.

A potential risk of active surveillance is the possibility that a biopsy needle might miss high-grade or large-volume tumors, leading to delayed therapy that can adversely affect outcomes. The most stringent classification criteria still lead to misdiagnosis in 16% to 42% of patients because of tumors that appear low risk on biopsy but have high-risk features at prostatectomy, the authors continued.

The ability of T2-weighted MRI to predict confirmatory biopsy results had not been examined, providing the impetus for the study by Vargas and colleagues.

They enrolled 388 consecutive men with newly diagnosed, clinically low-risk prostate cancer (initial-biopsy Gleason score ≤6, PSA <10 ng/mL, and clinical stage ≤T2a). Each patient underwent endorectal MRI prior to confirmatory biopsy.

Retrospectively, three radiologists individually reviewed the MRI results and assigned a score of 1 (definitely no tumor) to 5 (definite tumor). The investigators assessed inter-reader agreement and associations between MRI results and findings on confirmatory biopsies.

They found that an MRI score of 2 or less was associated with a negative predictive value of 0.96 to 1.00 and a specificity of 0.95 to 1.0. A score of 5 had high predictive accuracy for upgrading on confirmatory biopsy (0.87 to 0.98).

By multivariate analysis, higher MRI scores increased the odds of upgrading on confirmatory biopsy by 2.16 to 3.97).

More experienced readers had less inter-reader variability (AUC 0.76 to 0.76 versus 0.61 to 0.69 for least experienced).

Endorectal MRI had similar performance for predicting low-risk and very low-risk disease (Gleason <6, <3 positive scores, <50% involvement in all cores).

"Among patients initially diagnosed with clinically low-risk prostate cancer, those with tumors not clearly visualized on MRI were significantly more likely to demonstrate low-risk features on confirmatory biopsies, while patients with tumors clearly visualized on MRI were significantly more likely to have disease upgraded on confirmatory biopsy," the authors wrote in their discussion.

"In addition, our results confirm the importance of confirmatory biopsy in patients being evaluated for active surveillance. Among the patients who underwent prostatectomy within 6 months of MRI, the surgicopathological Gleason score was higher than that of the initial biopsy in 65% but was higher than that of the confirmatory biopsy in only 26%, suggesting that confirmatory biopsy provided a better estimate of the total tumor burden than did the initial biopsy."

The study was supported by the National Institutes of Health and the Peter Michael Foundation.

The authors had no relevant disclosures.

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