The value of endorectal MR imaging to predict positive biopsies in clinically intermediate-risk prostate cancer patients.

The aim of this study was to assess the effectiveness of endorectal MR imaging in predicting the positive biopsy results in patients with clinically intermediate risk for prostate cancer. We performed a prospective endorectal MR imaging study with 81 patients at intermediate risk to detect prostate cancer between January 1997 and December 1998. Intermediate risk was defined as: prostatic specific antigen (PSA) levels between 4 and 10 ng/ml or PSA levels in the range of 10-20 ng/ml but negative digital rectal examination (DRE) or PSA levels progressively higher (0.75 ng/ml year(-1)). A transrectal sextant biopsy was performed after the endorectal MR exam, and also of the area of suspicion detected by MR imaging. The accuracies were measured, both singly for MR imaging and combined for PSA level and DRE, by calculating the area index of the receiver operating characteristics (ROC) curve. Cancer was detected in 23 patients (28%). Overall sensitivity and specificity of endorectal MRI was 70 and 76%, respectively. Accuracy was 71% estimated from the area under the ROC curve for the total patient group and 84% for the group of patients with PSA level between 10-20 ng/ml. Positive biopsy rate (PBR) was 63% for the group with PSA 10-20 ng/ml and a positive MR imaging, and 15% with a negative MR exam. The PBR was 43% for the group with PSA 4-10 ng/ml and a positive MR study, and 13% with a negative MR imaging examination. We would have avoided 63% of negative biopsies, while missing 30% of cancers for the total group of patients. Endorectal MR imaging was not a sufficient predictor of positive biopsies for patients clinically at intermediate risk for prostate cancer. Although we should not avoid performing systematic biopsies in patients with endorectal MR imaging negative results, as it will miss a significant number of cancers, selected patients with a PSA levels between 10-20 ng/ml or clinical-biopsy disagreement might benefit from endorectal MR imaging.