Incorporating multiparametric MRI staging and the new histological Grade Group system improves risk-stratified detection of bone metastasis in prostate cancer

Abstract

$\textbf{BACKGROUND}$: There remains uncertainty on the need for bone staging in men with intermediate-risk prostate cancer. Current guidelines do not use mpMRI-staging information and rely on historic pathology grading. $\textbf{METHODS}$: We investigated the ability of mpMRI and the new Grade Group system to better predict bone metastasis status in a retrospective cohort study of 438 men with prostate cancer undergoing baseline mpMRI and isotope bone scintigraphy (BS). $\textbf{RESULTS}$: Including mpMRI-staging information significantly increased the specificity of bone metastasis detection from 3.0% to 24.2% (P<0.01) and sensitivity from 89.2% to 97.3%. The new Grade Group score demonstrated progressive increase in bone metastasis rates (P<0.001). A novel risk-stratification model combining Grade Groups, PSA and mpMRI staging shows promise in predicting bone metastasis and could potentially reduce BS usage by 22.4%-34.7%. $\textbf{CONCLUSIONS}$: Incorporating the new Grade Group system and mpMRI staging more accurately identified bone metastatic risk and suggests men with Grade Group ⩽2 and/or without radiological T3 disease could safely avoid routine bone staging.