The Promise of Pre-Biopsy MRI in a District General Hospital (DGH) Setting
Pre-biopsy multi-parametric magnetic resonance imaging (MP-MRI) is reported to have a negative predictive value (NPV) of 89% in prostate cancer diagnosis & can avoid a biopsy in around 25%. We aimed to replicate these results in a DGH.
108 men underwent MP-MRI & transperineal sector prostate biopsies (TP-Biopsy). The presence or absence of an index lesion on MP-MRI was reported. Clinically significant (CS) cancer was defined as Gleason ≥4+3 and/or Maximum tumour length ≥6mm and/or tumour ≥ 40% core involvement. MP-MRI results were compared with TP-Biopsy to derive sensitivity (S), specificity (Sp), positive predictive value (PPV) and NPV for MP-MRI.
MP-MRI demonstrated a lesion in 85. Of these 44 had cancer (22 were CS). Of the 23 with no lesion, 9 had cancer (4 were CS). For MP-MRI, sensitivity was 84.62% [95%CI 65.13-95.64], specificity was 23.17% [14.56-33.80], PPV was 25.88% [22.19-29.95] & NPV was 82.61% [63.98-92.70]. If MP-MRI is used as a screening test, a negative MP-MRI would allow 21.3% of men to avoid a biopsy with 3.7% fewer clinically significant cancers identified. If we defined CS cancer as any cancer with an intermediate risk or higher (PSA>10 or Gleason score >7 or clinical stage of >T2b), for MP-MRI the sensitivity was 78.95% [62.68-90.45], spefificity was 21.43% [12.52-32.87], PPV was 35.29% [30.77-40.10] & NPV was 65.22% [46.68-80.07].
The National Institute for Health and Care Excellence (NICE) advise against repeat prostate biopsy if the MRI is normal, however our results suggest 17-35% CS prostate cancer is missed by MP-MRI depending on definition used. Currently we feel MRI alone is an unreliable test to exclude CS prostate cancer in our unit.