Intraductal carcinoma of the prostate (IDC‐P) lowers apparent diffusion coefficient (ADC) values among intermediate risk prostate cancers

Background Prostatic intraductal carcinoma (IDC‐P) is an aggressive variant of prostate cancer (PCa) characterized by proliferation of malignant cells within prostatic ducts/acini and nucleomegaly. Purpose/Hypothesis To compare apparent diffusion coefficient (ADC) values and Prostate Imaging and Data Reporting System (PI‐RADS) v. 2 scores in intermediate risk (International Society of Urological Pathology [ISUP] Grade Group [GG] 2 and 3) PCa with/without IDC‐P to determine if IDC‐P alters the MRI appearance of PCa. Study Type Retrospective, case–control. Population Fifteen consecutive men with ISUP GG 2/3 (Gleason score 3+4 = 7 [ N = 4], 4+3 = 7 [ N = 11]) PCa with IDC‐P diagnosed at radical prostatectomy were compared with: 1) ISUP GG 2/3 PCa without IDC‐P (matched for percentage Gleason pattern 4), and 2) ISUP GG 4 and 5 (Gleason score 8/9) PCa without IDC‐P. Field Strength/Sequence 3T multiparametric MRI. Assessment Two blinded radiologists (R1/R2) measured mean ADC, ADC.ratio (ADC.tumor/ADC.normal peripheral zone) and assigned PI‐RADS v2 scores. Statistical Tests: Chi‐square and analysis of variance (ANOVA). Results There were no differences in age, prostate serum antigen, tumor size, or stage between groups ( P = 0.063‐0.912). Tumors with IDC‐P had lower mean ADC and ADC.ratio (0.741 ± 0.152 mm 2 /sec and 0.44 ± 0.07) compared with ISUP GG 2/3 tumors without IDC‐P (0.888 ± 0.167 mm 2 /sec and 0.62 ± 0.14), P = 0.012 and <0.001; and did not differ compared with ISUP GG 4/5 tumors (0.705 ± 0.141 mm 2 /sec and 0.44 ± 0.08), P = 0.509 and 0.868. Tumors with IDC‐P were nearly all PI‐RADS v2 score 5 (14/15) compared with ISUP GG 2/3 tumors without IDC‐P (10/15 R1, 8/15 R2) and GG 4/5 tumors (9/15), ( P = 0.040 = 0.092). Agreement in PI‐RADS v2 scoring was moderate (K = 0.68). Data Conclusion ISUP GG 2 and 3 (intermediate risk, Gleason score 7) PCa with IDC‐P have lower ADC compared with tumors without IDC‐P with a similar percentage of Gleason pattern 4 and resemble ISUP GG 4 and 5 high risk tumors on MRI. IDC‐P lowers ADC values among intermediate risk prostate cancers. Level of Evidence : 3 Technical Efficacy Stage : 2 J. Magn. Reson. Imaging 2019;50:279–287.