Faculty Bibliography

Approximately 15% of men with newly diagnosed prostate cancer have high-risk disease. Imaging is critically important for the diagnosis and staging of these patients, and also for the selection of management. While established prostate cancer staging guidelines have increased the appropriate use of imaging, underuse for high-risk prostate cancer remains substantial. Several factors affect the utility of initial diagnostic imaging, including the variable definition of high-risk prostate cancer, variable guideline recommendations, poor accuracy of existing imaging tests, and the difficulty in validating imaging findings. Conventional imaging modalities, including CT and radionuclide bone scan, have been employed for local and metastatic staging, but their performance characteristics have generally been poor. Emerging modalities including multiparametricMRI, positron emission tomography (PET)-CT, and PET-MRI have shown increased diagnostic accuracy and could improve accuracy in staging patients with high-risk prostate cancer.

PURPOSE OF REVIEW: In recent years, multiparametric magnetic resonance imaging (mpMRI) of the prostate has shown promise as a modality to identify areas of suspicion within the gland which correlate with cancer location and disease extent. However, optimal individualization of prostate biopsy using mpMRI relies on aligning the relative benefits of MRI-targeted approaches with the goals of biopsy. RECENT FINDINGS: For men with prior negative biopsies, mpMRI allows improved detection of occult high-grade cancers missed by repeat systematic biopsy but also has the potential to identify men who will not benefit from repeat biopsy due to a low likelihood of significant disease. For men with prior low-grade cancer diagnosis, the addition of MRI-targeted biopsy may identify those who are poor candidates for active surveillance by detecting high-risk disease without serial biopsies. For men without prior biopsy, mpMRI and targeted biopsy may help improve high-grade cancer diagnosis and significantly limit the detection of low-risk disease. SUMMARY: mpMRI of the prostate is a promising tool to address many of the shortcomings of traditional systematic prostate biopsy. Biopsy history plays a critical role in determining how to assess the potential advantages and disadvantages of prostate mpMRI in the context of each patient. Although these benefits have been suggested by published clinical outcomes data, there is a need for prospective validation of mpMRI and MRI-targeted biopsy in comparison with the current approach of systematic biopsy for all men, to define new paradigms for prostate cancer detection and risk stratification.

AIM: To evaluate the performance of normalised apparent diffusion coefficient (ADC) values for prostate cancer assessment when performed by independent observers blinded to histopathology findings. MATERIALS AND METHODS: Fifty-eight patients undergoing 3 T phased-array coil magnetic resonance imaging (MRI) including diffusion-weighted imaging (DWI; maximal b-value 1000 s/mm2) before prostatectomy were included. Two radiologists independently evaluated the images, unaware of the histopathology findings. Regions of interest (ROIs) were drawn within areas showing visually low ADC within the peripheral zone (PZ) and transition zone (TZ) bilaterally. ROIs were also placed within regions in both lobes not suspicious for tumour, allowing computation of normalised ADC (nADC) ratios between suspicious and non-suspicious regions. The diagnostic performance of ADC and nADC were compared. RESULTS: For PZ tumour detection, ADC achieved significantly higher area under the receiver operating characteristic curve (AUC; p=0.026) and specificity (p=0.021) than nADC for reader 1, and significantly higher AUC (p=0.025) than nADC for reader 2. For TZ tumour detection, nADC achieved significantly higher specificity (p=0.003) and accuracy (p=0.004) than ADC for reader 2. For PZ Gleason score >3+3 tumour detection, ADC achieved significantly higher AUC (p=0.003) and specificity (p=0.005) than nADC for reader 1, and significantly higher AUC (p=0.023) than nADC for reader 2. For TZ Gleason score >3+3 tumour detection, ADC achieved significantly higher specificity (p=0.019) than nADC for reader 1. CONCLUSION: In contrast to prior studies performing unblinded evaluations, ADC was observed to outperform nADC overall for two independent observers blinded to the histopathology findings. Therefore, although strategies to improve the utility of ADC measurements in prostate cancer assessment merit continued investigation, caution is warranted when applying normalisation to improve diagnostic performance in clinical practice.