BACKGROUND/AIM:The high sensitivity cardiac troponin T (Hs-cTnT) is a myocardial damage biomarker that could have a predictive value in patients who undergo radiotherapy for left sided breast cancer. The aim of this study was to evaluate the early effect of left whole breast radiotherapy (WB-RT) on serum Hs-cTnT levels and its correlation with pre-existing factors.PATIENTS AND METHODS:The study was conducted from December 2017 to May 2018. Forty-five patients with early stage left-sided breast cancer who received adjuvant breast hypofractionated RT without prior chemotherapy were included. Serum levels of Hs-cTnT were obtained before, weekly during RT, and within one week after the end of treatment. Considering the physiological variations of serum levels, an increase in Hs-cTnT (∆Hs-cTnT) of more than 30% from the baseline value was chosen as a threshold. The main cardiovascular risk factors were recorded. Dose volume histograms (DVHs) were used to provide a quantitative analysis for the whole heart, left ventricle, and left anterior descending artery (LAD).RESULTS:Twelve of 45 patients (26.6%) showed a ∆Hs-cTnT ≥30%. The maximum Hs-cTnT level was recorded in the last week of treatment. ∆Hs-cTnT was strongly associated with heart V5 (p=0.05) and hypertension (p=0.05). Multivariate analysis confirmed the importance of the heart V5 and correlated with ∆Hs-cTnT.CONCLUSION:The increase in Hs-cTnT serum levels during adjuvant WB-RT suggested a correlation with the cardiac radiation dose in chemotherapy-naive breast cancer patients. A longer follow-up is needed to correlate Hs-cTnT values with cardiac events.