S186
Clinical - Biomarkers of clinical response
ESTRO 2026
1 Department of Oncology, Tampere University Hospital, Tampere, Finland. 2 Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland. 3 Heart Hospital, Tampere University Hospital, Tampere, Finland. 4 Heart and Lung Center, Helsinki University Central Hospital, Helsinki, Finland. 5 The Immunopharmacology Research Group, Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland. 6 Faculty of Social Sciences, Tampere University, Tampere, Finland. 7 Research, Development and Innovation Center, Tampere University Hospital, Tampere, Finland Purpose/Objective: The long-term survival of breast cancer patients has improved notably over the past decades, largely due to advances in diagnostics and management. Adjuvant radiotherapy (RT) is an essential component of breast cancer treatment for most patients and has been shown to reduce breast cancer recurrence and mortality [1]. However, even with contemporary RT techniques, incidental cardiac radiation exposure remains associated with increased cardiac morbidity and mortality [2]. Identifying patients at risk for RT- induced cardiotoxicity is therefore crucial for improving survivorship care.ST2 is a member of the interleukin-1 receptor family. Circulating ST2 levels increase after myocardial injury [3] and increased ST2 levels predict all-cause and cardiovascular mortality in heart failure patients [4]. However, its role in predicting RT-induced cardiotoxicity remains unclear. We evaluated the association between ST2, RT dose parameters, and cardiac function during six years of follow-up after adjuvant breast cancer RT. Material/Methods: Sixty patients treated with adjuvant breast RT without chemotherapy were included in this prospective study (Table 1). Detailed information on radiation doses to cardiac structures, ST2 levels and echocardiographic parameters before and immediately after RT, and at three and six years in the follow-up were collected.
Results: ST2 levels increased significantly during the follow-up from 14.15 (6.00) ng/ml at baseline to 15.54 (5.43) ng/ml at 6 years (p<0.001) (Table 2). The ST2 change between the end of RT and three years correlated with RT doses, including mean LAD dose ( ρ =0.324, p=0.011), V20 Gy LAD ( ρ =0.391, p=0.002), V20 Gy heart ( ρ =0.295, p=0.022), and V20 Gy left ventricle ( ρ =0.259, p=0.046).The increase in ST2 levels from the end of RT to three years correlated with worsening global longitudinal strain (GLS) at six years ( ρ =0.345, p = 0.013). Furthermore, patients with ≥ 10 % increase in ST2 from the end of RT to three years predicted a more significant decline in GLS at six years (3.43% vs. 0.27% absolute change, p=0.009).
Conclusion: ST2 levels increased after breast cancer RT in
association with cardiac radiation doses. In addition, elevated ST2 levels were associated with long-term subclinical myocardial dysfunction at six years. These findings support ST2 as a potential biomarker of RT- induced cardiotoxicity and warrant validation in larger patient cohorts. References: [1] Darby S et al. Effect of radiotherapy after breast- conserving surgery on 10-year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10,801 women in 17 randomized trials. Lancet 2011;378:1707–16. [2] Belzile-Dugas E, Eisenberg MJ. Radiation-Induced Cardiovascular Disease: Review of an Underrecognized Pathology. J Am Heart Assoc 2021;10(18):e021686[3] Weinberg EO et al. Expression and regulation of ST2, an interleukin- 1 receptor family member, in cardiomyocytes and
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