Cardiac Side Effects of Systemic Therapy in Early-Stage Breast Cancer

Background: Anthracyclines and anti-HER2 agents are cornerstone treatments for early-stage breast cancer but carry meaningful risk of cancer therapy-related cardiac dysfunction (CTRCD). Cardiotoxicity is often initially subclinical, with left ventricular ejection fraction (LVEF) decline appearing late, after irreversible myocardial damage may have occurred. The 2022 European Society of Cardiology (ESC) Cardio-Oncology Guidelines recommend Global Longitudinal Strain (GLS) as a more sensitive parameter than LVEF for early detection of cardiac dysfunction. A relative reduction in GLS can occur weeks to months before clinically apparent LVEF decline. While echocardiography provides functional assessment of the heart, it offers limited insight into the molecular mechanisms underlying cardiac injury. Circulating microRNAs (miRNAs) are emerging as candidate biomarkers reflecting cardiomyocyte injury, oxidative stress, and fibrosis. Although several studies have evaluated cardiotoxicity from anthracyclines and anti-HER2 therapies, most have been retrospective and focused solely on LVEF changes. Prospective studies that simultaneously assess GLS and circulating miRNAs are limited, as are head-to-head comparisons of cardiac effects across different chemotherapy regimens at both functional and molecular levels. Rationale: This study addresses these gaps by evaluating cardiac effects of systemic therapy in early-stage breast cancer patients using both functional (echocardiographic) and molecular (miRNA) parameters in a prospective design. The findings are expected to contribute to early identification of cardiotoxicity, identification of high-risk patient subgroups, and development of personalized cardio-oncology surveillance strategies. Study Procedures: Patients are assessed at four time points: baseline (prior to systemic therapy initiation), Month 3, Month 6, and Month 12. At each visit, the following procedures are performed: Echocardiographic Assessment: Transthoracic echocardiography is performed by experienced cardiologists using a standardized protocol. LVEF is measured using Simpson's biplane method, and GLS is measured using speckle-tracking analysis. Additional parameters including E/A ratio, TAPSE, and QTc interval are also recorded. Circulating microRNA Analysis: Peripheral venous blood samples are collected in EDTA tubes during routine blood draws (no additional needle stick required). Total RNA is isolated using a commercial total nucleic acid isolation kit, and RNA concentration and purity are assessed via UV spectrophotometry. Reverse transcription is performed using a microRNA cDNA synthesis kit. Quantitative real-time PCR is performed using SYBR Green PCR kit on a LightCycler 480 II system. Expression levels of the following miRNAs are measured: miR-34a, miR-146a, miR-21, miR-155, miR-1, miR-133a, miR-208a, and miR-499. These miRNAs were selected based on their reported associations with cardiac injury, fibrosis, oxidative stress, and inflammation in the cardio-oncology literature. U6 small nuclear RNA serves as the normalization control. Relative quantification is calculated using the 2\^(-ΔΔCt) method. Cardiac Biomarkers: High-sensitivity troponin I and NT-proBNP are measured at each visit. Routine Laboratory Assessments: Complete blood count, renal function (creatinine, eGFR), and liver function (ALT) are obtained. Patient-Reported Outcomes: Quality of life is assessed using the EORTC QLQ-C30 (general cancer module) and EORTC QLQ-BR42 (breast cancer-specific module). Additional patient-reported assessments include the EORTC QLQ-FA12 (cancer-related fatigue), EORTC QLQ-SH22 (sexual health), PHQ-4 (anxiety/depression), PSQI (sleep quality), and FACT-Cog (cognitive function). Adverse Event Monitoring: All treatment-emergent adverse events are graded according to CTCAE version 5.0. Treatment: The study does not modify treatment selection, dose, or duration. All patients receive standard-of-care systemic therapy (anthracycline-containing or anthracycline-free regimens, with or without anti-HER2 agents) determined by their treating oncologist based on disease characteristics and current clinical guidelines. For analytic purposes, patients are sub-grouped by chemotherapy regimen for comparative analyses. Statistical Considerations: A total of 100 patients are planned for enrollment. miRNA expression differences between groups are analyzed using REST 2009 v2.013 software and confirmed with GeneGlobe Data Analysis Center. Continuous variables not normally distributed are compared using Mann-Whitney U test (two groups) or Kruskal-Wallis test with Dunn post-hoc tests (three or more groups). Statistical significance is set at p \< 0.05.