Use of whole-body MRI to evaluate residual tumor burden after initial systemic therapy in polymetastatic hormone-sensitive prostate cancer

Objectives: Treatment options for metastatic hormone-sensitive prostate cancer (mHSPC) have expanded, with evidence supporting prostate radiotherapy in low-volume disease. However, evidence for consolidative radiotherapy to residual sites in patients rendered oligometastatic after systemic therapy is lacking. Advanced imaging with WB-MRI and PSMA PET/CT enables more accurate assessment of tumor burden and response. Methods: This feasibility study assessed response to initial systemic treatment with an ARPI or docetaxel in 29 patients with polymetastatic (>5 metastases) HSPC. PSA and WB-MRI response using MET-RADS-P criteria were recorded. Results: A total of 20/29 (69.0.%) of patients were down-risked to oligometastatic disease (≤5 sites) after a median of 5.5 (IQR 5-5.8) months, identified on WB-MRI. Median PSA was 0.2 ng/mL (IQR 0.1-0.7) in down-risked patients vs 1.5 ng/mL (IQR 1.1-84) in those not down-risked. Residual intraprostatic disease was seen in 55% (11/20) of down-risked patients. Conclusions: Most patients were down-risked on WB-MRI, supporting the existence of an induced oligometastatic state and providing rationale for the STAR TRAP randomized trial (ISRCTN16448082), which will assess the role of consolidative radiotherapy in this setting. Advances in knowledge: WB-MRI correlates with PSA response and shows potential as an imaging biomarker in mHSPC in this small feasibility study. © The Author(s) 2026. Published by Oxford University Press on behalf of the British Institute of Radiology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/pages/standard-publication-reuse-rights)