Adding an MRI exam to the initial clinical evaluation of men thought to have low-risk prostate cancer can help identify which of them are the best candidates for active surveillance, according to study findings published online Oct. 3 in the Journal of Urology.
In a retrospective study of 388 men believed to have low-risk prostate cancer, tumors that were clearly visualized on an initial MRI were significantly more likely to be upgraded or upstaged on later confirmatory biopsy, and to prompt prostatectomy at that time. In contrast, tumors that could not be clearly visualized on MRI at the initial evaluation were significantly more likely to remain low grade on later confirmatory biopsy, and lent themselves to active surveillance rather than surgery, said Dr. Hebert Alberto Vargas of the department of radiology, Memorial Sloan-Kettering Cancer Center, New York, and his associates.
"These results 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," they noted.
Initial biopsy samples of prostate cancers can miss areas of high-grade cancer, and "even the most stringent criteria misclassify 16%-42% of cases, which, despite low-risk features on initial biopsy, [are found to have] unfavorable pathological features at radical prostatectomy." Accordingly, some treatment centers recommend a second, confirmatory biopsy before pursuing active surveillance, the investigators said.
In one study of the issue, 27% of men with very low-risk features on initial biopsy proved to have upgraded or upstaged tumors at confirmatory biopsy.
Dr. Vargas and his colleagues decided to examine retrospectively whether standard transrectal T2-weighted MRI of the prostate would be useful in predicting which tumors were likely to be upgraded or upstaged on confirmatory biopsy.
The investigators identified 388 cases in their institution’s database in which men had an initial Gleason score of 6 or less on initial prostate biopsy performed in 1999-2010, had a prostate-specific antigen level less than 10 ng/mL, and had a confirmatory biopsy performed within 6 months of the initial biopsy.
Three radiologists independently interpreted the archived MRI scans and assigned each one a score indicating that tumor tissue was definitely evident, probably evident, definitely absent, probably absent, or indeterminate.
For all three radiologist readers, MRI scores indicating the probable or definite absence of tumor were highly predictive that confirmatory biopsy would show only very low-risk features and that active surveillance would be sufficient for those patients. In contrast, in a multivariate analysis, MRI scores showing the probable or definite presence of tumor were highly predictive that confirmatory biopsy would find upgraded or upstaged cancer (odds ratio, 2.16-3.97), and that radical prostatectomy would be recommended, the investigators said (J. Urol. 2012 Oct. 3 [doi:10.1016/j.juro.2012.07.024]).
Notably, one of the three radiologists, who had read only about 50 prostate MRI scans at the time of this study, had consistently less accurate readings than either of the other radiologists. The second radiologist had a fellowship in body imaging plus specialized training in prostate imaging, and had interpreted approximately 500 prostate MRIs. The third radiologist had completed a fellowship in genitourinary radiology and had read more than 5,000 prostate MRI scans.
The study findings thus confirm the importance of training and experience for the accurate interpretation of MRI scans of the prostate, Dr. Vargas and his associates noted.
This study was supported by the National Institutes of Health. No financial conflicts were reported.