MRI Helps Identify Men for Active Surveillance

Endorectal magnetic resonance imaging (MRI) can help predict pathological upgrading on a second (confirmatory) prostate biopsy in men with low-risk cancer being considered for active surveillance, according to a new study.

The visibility of the tumor is key to confirming risk.

All men in the study were initially diagnosed with clinically low-risk disease. Men with tumors not clearly visualized on MRI were more likely to demonstrate low-risk features on second biopsy, whereas men with clearly visible tumors were more likely to have their disease upgraded on second biopsy.

Dr. Hebert Vargas

"MRI is a tool that evidently helps confirm who is and is not a good candidate to be watched (and thus avoid surgery)," first author Hebert A. Vargas, MD, from the Department of Radiology at the Memorial Sloan-Kettering Cancer Center in New York City, told Medscape Medical News.

"The key thing here," he explained, "is that men who have suspicious PSA [prostate specific antigen] test results get biopsied. If low-grade cancer is found, then they are candidates for watchful waiting [active surveillance] and can avoid surgical removal of prostate."

The success of active surveillance as a management strategy for prostate cancer hinges on the accurate identification of patients with low-risk disease that is unlikely to progress, according to the researchers.

The risk that an initial prostate biopsy will underestimate the true extent of disease might keep some men (and their doctors) from opting for active surveillance. It's a valid concern, the researchers note.
A recent study (Eur Urol. 2011;60:291-303) found that even the most stringent criteria misclassify 16% to 42% of cases that, despite low-risk features on initial biopsy, have unfavorable pathologic features at radical prostatectomy, the researchers write.

To improve the detection of large or high-grade cancers, some centers recommend a confirmatory prostate biopsy before starting active surveillance.

The Sloan-Kettering team believes their study is the first to assess the value of endorectal T2-weighted MRI in predicting the upgrading, on confirmatory biopsy, of men with low-risk prostate cancer (initial biopsy Gleason score of 6 or lower, PSA below 10 ng/mL, clinical stage T2a or lower).

Study Details
 
The study involved 388 consecutive men (mean age, 60.6 years). Three radiologists independently and retrospectively scored tumor visibility on endorectal MRI using a 5-point scale (1, definitely no tumor; 5, definitely tumor). Associations between MRI scores and confirmatory biopsy results were evaluated.

The researchers report that confirmatory biopsy findings fit the National Comprehensive Cancer Network criteria for low-risk disease in 309 men (80%) and for very-low-risk disease in 239 men (62%). In 124 men (32%), no cancer was found on second biopsy. In 79 men (20%), confirmatory biopsy led to an upgrading of disease (i.e., at least 1 core with a Gleason score of 7 or higher).
Of the 129 men (33%) who underwent prostatectomy within 6 months of the MRI, the surgicopathologic Gleason score was higher than that of the initial biopsy in 65% of men, but was higher than that of the confirmatory biopsy in only 26%. This suggests that the confirmatory biopsy provides a better estimate of the total tumor burden, the researchers say.

Importantly, an MRI score of 2 or less had a high negative predictive value (0.96 to 1.00) and specificity (0.95 to 1.00) for upgrading on confirmatory biopsy, whereas an MRI score of 5 was highly sensitive for upgrading on confirmatory biopsy (0.87 to 0.98), the researchers note.
On multivariate analysis, patients with higher MRI scores were significantly more likely to have their tumor upgraded on confirmatory biopsy (odds ratio, 2.16 to 3.97). Conversely, lower MRI scores predicted low-risk and very-low-risk prostate cancer.

The researchers saw higher interreader agreement and diagnostic performance for the 2 more experienced readers (kappa, 0.41 to 0.61; area under the curve [AUC], 0.76 to 0.79) than for the least experienced reader (kappa, 0.15 to 0.39; AUC, 0.61 to 0.69). This confirms previous reports on the importance of training and experience for accurate interpretation of prostate MRI, they say. The least experienced reader had read only about 50 prostate MRI scans before the study, whereas the one of the more experienced readers had read roughly 500 scans and the other had read more than 5000.

The results of this study "suggest that MRI of the prostate, if read by radiologists with appropriate training and experience, could help determine [active surveillance] eligibility and obviate the need for confirmatory biopsy in substantial numbers of patients," the researchers conclude.
They hope their study will encourage other studies assessing the incremental value of MRI in larger cohorts of prostate cancer patients.

In an accompanying editorial, Guillaume Ploussard, MD, PhD, from the Department of Urology at CHU Saint-Louis Hospital in Paris, France, notes that the "primary issue is to reduce the number of clinical settings in which the urologist and the patient will face the situation of an increased PSA and an uncertain diagnosis." He adds that "targeted biopsy strategies are designed to optimize the detection of clinically significant prostate cancer."

This study suggests that MRI "might help limit the risk of biopsy undergrading due to the good discriminating power for high-grade/high-volume prostate cancer," writes Dr. Ploussard.
"In cases of normal signal in the whole gland, the patient might be reassured and rebiopsy delayed. In cases of a suspicious nodule, rebiopsy would be better justified with a risk of clinically significant disease, and biopsy cores could target suspicious zones."