Vol. 7, Issue 2, Part B (2025)

Background: Trastuzumab (TRZ) enhances survival outcomes in HER2-positive breast cancer however carries a substantial risk of cardiotoxicity that may not be detected by left ventricular ejection fraction (LVEF) alone. Objectives: To identify early predictors of subclinical left ventricular dysfunction during TRZ therapy. Methods: This prospective observational study involved 100 women starting TRZ with baseline LVEF > 55% and normal high-sensitivity troponin T (hs-TnT) who underwent assessments at baseline, 3, and 6 months. Testing included clinical evaluation, hs-TnT, LVEF, and global longitudinal strain (GLS). Results: hs-TnT was elevated in 21% at 3 months and 22% at 6 months (p<0.001 across time). LVEF declined from 61.28±2.56% at baseline to 58.33±3.98% (3 months) and 55.18±6.90% (6 months) (both p<0.001). GLS worsened from −19.89±0.85% to −17.87±2.29% and −17.44±2.34% at 3 and 6 months (both p<0.001). A ≥15% GLS reduction occurred in 24% at 3 months and 27% at 6 months; overall cardiotoxicity occurred in 27%. On univariate analysis, 3-month hs-TnT, 6-month hs-TnT, ≥15% GLS drop at 3 months, and ≥15% GLS drop at 6 months predicted cardiotoxicity (all p<0.001). In multivariate analysis, only a ≥15% GLS fall at 6 months remained independently predictive (B = 9.080; 95% CI 3.829-15.497; p = 0.002). Conclusions: Serial GLS and hs-TnT detect early myocardial injury during TRZ therapy. A ≥15% GLS decline particularly by 6 months independently predicts cardiotoxicity and may refine risk stratification beyond LVEF.