S195
Clinical - Biomarkers of clinical response
ESTRO 2026
diagram
grade 2 dermatitis and no correlation to genetic variants or inflammatory biomarkers. References: 1. Brunt AM et al. FAST-Forward Trial Management Group. Acute skin toxicity associated with a 1-week schedule of whole breast radiotherapy compared with a standard 3-week regimen delivered in the UK FAST- Forward Trial. Radiother Oncol. 2016;120(1):114-8. 2. Andreassen CN et al. Individual patient data meta- analysis shows a significant association between the ATM rs1801516 SNP and toxicity after radiotherapy in 5456 breast and prostate cancer patients. Radiother Oncol. 2016;121(3):431-9.3. Hu JJet al. Association Between Inflammatory Biomarker C-Reactive Protein and Radiotherapy-Induced Early Adverse Skin Reactions in a Multiracial/Ethnic Breast Cancer Population. J Clin Oncol. 2018;36(24):2473-82. Keywords: side-effects, radiosensitivity, normal tissue The role of PSMA PET/CT and WB-MRI as imaging biomarkers of response in metastatic hormone- sensitive prostate cancer: a systematic review Claire Thompson, Saranya Ravindra, Julia Murray Radiotherapy & Imaging, Royal Marsden Hospital, Sutton, United Kingdom Purpose/Objective: Prostate-specific membrane antigen positron emission tomography with computed tomography (PSMA PET/CT) and whole-body magnetic resonance imaging (WB-MRI) are increasingly used for prostate cancer staging due to greater sensitivity and specificity compared with conventional imaging (CT and bone scan)1, 2. However, their role in evaluating treatment response in metastatic hormone-sensitive prostate cancer (mHSPC) is not well established. This systematic Digital Poster 3466 review examines the current evidence supporting PSMA PET/CT and WB-MRI as imaging biomarkers of
Results: After screening 1885 abstracts and reviewing 100 full- text articles, 24 studies met inclusion criteria: 21 involving PSMA PET/CT and 3 involving WB-MRI. Although all included studies contained patients with mHSPC, several also included individuals with localised disease or castration-resistant prostate cancer. Treatment regimens varied both between and within studies, as did timing of response imaging.Of the PSMA PET/CT studies, 19/21 were retrospective and 2/21 prospective. Median sample size was 20 (Range 7- 138; IQR 10-46.5) patients. Response evaluation involved changes in quantitative PET parameters, including SUVmax, SUVmean, PSMA-total lesion (PSMA-TL) and PSMA-tumour volume (PSMA-TV) using a variety of criteria to define response. Most studies (19/21) compared PSMA PET/CT response with prostate-specific antigen (PSA) response, while others compared imaging with conventional radiological response or survival outcomes.The three WB-MRI studies, all randomised trials (median n=37 patients), used diffusion-weighted and T1-weighted imaging metrics (including b-value, apparent diffusion coefficient, relative fat fraction) and lesion count to assess response. All three demonstrated a significant association between WB-MRI response and overall survival. Conclusion: Current evidence supporting PSMA PET/CT for treatment response assessment in mHSPC is limited by mostly retrospective design, small sample sizes, heterogeneous patient populations and non- standardised response criteria. WB-MRI has emerging RCT-level evidence indicating prognostic relevance. Future randomised trials incorporating both modalities are required to define their validity as response biomarkers in mHSPC. References: 1 Padhani AR, Lecouvet FE, Tunariu N, Koh DM, De Keyzer F, Collins DJ, et al. METastasis Reporting and Data System for Prostate Cancer: Practical Guidelines for Acquisition, Interpretation, and Reporting of Whole-body Magnetic Resonance Imaging-based Evaluations of Multiorgan Involvement in Advanced Prostate Cancer. Eur Urol 2017;71:81–922 Hofman MS, Lawrentschuk N, Francis RJ, et al. Prostate-specific membrane antigen PET-CT in patients with high-risk prostate cancer before curative-intent surgery or
response in mHSPC. Material/Methods:
A systematic search of PubMed, Cochrane and Web of Science was undertaken. Inclusion criteria were: (1) randomised controlled trials or retrospective/prospective cohort studies, (2) studies including patients with mHSPC undergoing therapy and assessed with PSMA PET/CT or WB-MRI for treatment response, and (3) a reported comparison with biochemical response, conventional imaging response, or survival outcomes. Exclusion criteria were review articles, editorials, case reports/series, non- English language studies, and studies limited to non- metastatic or castration-resistant prostate cancer. The review followed PRISMA guidelines.Figure 1. Study flow
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