Whole-Body Diffusion-Weighted Magnetic Resonance Imaging (MRI) as a Response Biomarker for Metastatic Prostate Cancer

The skeleton is the most frequent organ of distal metastases in prostate cancer, often representing the only site of metastatic disease. Still, assessment of response and progression to therapies in bone metastases remains a major unmet need, to aid treatment switch decisions, detecting primary/secondary resistance and to optimize drug development. The currently used standard imaging techniques, computed tomography (CT) and bone scintigraphy (BS), do not depict the true extent of bone metastases and are suboptimal in capturing biological changes occurring in response to treatment. This results in treatment switch decisions too often being based on PSA changes, which is neither a surrogate of survival, nor an optimal response biomarker.Diffusion-weighted imaging (DWI) is a functional magnetic resonance imaging (MRI) technique that studies the movement of water molecules within a tissue and provides valuable information about the tissue microstructure and cellularity. Whole body MRI with DWI is highly accurate for bone metastases detection, outperforming the standard CT and BS and other imaging techniques when assessing bone metastases. The investigators hypothesise that DWI changes are a response biomarker in bone metastases from metastatic castration resistant prostate cancer (mCRPC); these DWI changes can be detected as early as after 4 weeks of systemic treatment.