Accuracy of 3 Tesla pelvic phased-array multiparametric MRI in diagnosing prostate cancer at repeat biopsy
Objective. Although the ideal biopsy scheme should perform targeted biopsies to diagnose only significant PCa reducing the number of unnecessary procedures (1), still today, the serum biomarkers and imaging lack in accuracy especially in the early stage of disease. Recently, multiparametric magnetic resonance imaging (mMRI) using pelvic phased -array coil (mpMRI) or endorectal coil (meMRI) has been proposed to improve the detection rate for PCa (2-8) to diagnose significant cancer in patients submitted to repeat biopsy.
In this study, the accuracy of mpMRI to diagnose significant PCa in men who underwent repeat saturation biopsy (SPBx) for persistent suspicion of PCa was prospectively evaluated; in detail, detection for cancer of saturation prostate biopsy was compared with that obtained performing targeted mpMRI-guided biopsy
Methods and results
Methods and results. From June 2011 to December 2013, 168 patients (median 65 years) with negative digital rectal examination underwent repeat transperineal saturation biopsy (SPBx; median 28 cores) (9) for persistently high or increasing PSA values, PSA >10 ng/ml or PSA values between 4.1-10 or 2.6-4 ng/ml with free/total PSA < 25% and < 20%, respectively (10). All patients underwent mpMRI using a 3.0 Tesla scanner equipped with surface 16 channels phased-array coil and lesions suspicious for PCa were submitted to additional targeted biopsies. To ensure that histopatological findings matched with mpMRI images (cognitive fusion) the assessment of radiological images and SPBx scheme were performed dividing the prostate into 14 regions (8); moreover, in the presence of mpMRI lesions suspicious for cancer (PI-RADS score 4 and 5) (11), 3-4 (median 3.5 cores) targeted TRUS guided-biopsies in addition to standard SPBx were performed.
A T1c PCa was found in 66 (39%) cases (median PSA equal to 8.9 ng/mL); SPBx and mpMRI-suspicious targeted biopsy diagnosed 60 (91%) and 52 (78.8%) cancers missing 6 (all of the anterior zone) and 14 cancers (12 and 2 of the lateral margins and anterior zone), respectively; in detail, mpMRI missed 12 (18.1%) PCa charaterized by microfocal (1 positive core with greatest percentage of cancer and Gleason score equal to 5% and 6, respectively) disease at risk for insignificant cancer. The diameter of the suspicious mpMRI lesion was directly correlated to the diagnosis of PCa with poor Gleason score (p <0.05); detection rate of cancer for each suspicious mpMRI core was 35.3%. Diagnostic accuracy, sensitivity, specificity, positive and negative predictive value of mpMRI in diagnosing PCa was 75.7%, 82.5%, 71.8%, 78.9%, 87.9%, respectively.
Discussion. In the last years, mMRI has gained growing importance in PCa diagnosis and staging using mpMRI or meMRI (2-8); recently, 3 Tesla MRI has been suggested in the reevaluation of patients enrolled in active surveillance protocols, and is highly representative of the true GS and predictive of significant PCa. The estimated sensitivity and specificity for PCa detection by MRI varies between 57% and 100% vs 44% and 96%, respectively (3); therefore, there is increasing interest in using MRI, especially in men with prior negative prostate biopsy and persistent suspicion of PCa.
In our series, mpMRI detected 52 out 66 PCa; in detail, mpMRI in comparison with SPBx diagnosed 4 significant cancer of the anterior zone missing 12 cancers charaterized by microfocal biopsy histological disease at risk for insignificant PCa. In addition, a correlation between mpMRI suspicious lesion diameter vs PCa diagnosis and tumour grade was found. Some limitations and considerations of the present study deserve mention. Firstly, we do not know the true diagnostic accuracy of mpMRI in PCa diagnosis because the detection rate for cancer was compared with SPBx results. Secondly, we do not know if the false-positive rate (23.8% of the cases) of mpMRI was secondary to false-negative SPBx results or was biased because an MRI imaging/ultrasound fusion-guided biopsy, theoretically more accurate, was not performed (12).
In conclusion, mpMRI improved SPBx accuracy in diagnosing significant anterior PCa; the diameter of mpMRI suspicious lesion resulted significantly predictive of aggressive cancers.
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