The goal of this observational study is to evaluate cardiac side effects in women with early-stage breast cancer who receive systemic chemotherapy and/or anti-HER2 therapy as part of their standard cancer care.

The main questions it aims to answer are:

Can changes in Global Longitudinal Strain (GLS) on echocardiography detect early cardiac dysfunction before a drop in left ventricular ejection fraction (LVEF) becomes apparent? Are changes in circulating microRNA levels in the blood associated with early cardiac dysfunction during cancer treatment? Does cardiac dysfunction occur more frequently with anthracycline-containing chemotherapy compared to anthracycline-free regimens?

Participants already receiving standard chemotherapy and/or anti-HER2 therapy as part of their routine cancer care will undergo echocardiography (LVEF and GLS), provide blood samples for microRNA analysis, and complete quality of life questionnaires at four time points: before treatment (baseline), and at 3, 6, and 12 months after starting treatment.

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.

Inclusion Criteria:

• Histologically confirmed diagnosis of breast cancer
• Stage I, II, or III disease
• Planned neoadjuvant or adjuvant chemotherapy and/or HER2-targeted systemic therapy
• Baseline transthoracic echocardiographic left ventricular ejection fraction (LVEF) ≥ 50%
• Age ≥ 18 years
• Able and willing to provide written informed consent

Exclusion Criteria:

• Metastatic (Stage IV) breast cancer
• Pre-existing heart failure or clinically significant cardiac disease
• Prior exposure to chemotherapy or other cardiotoxic systemic therapy
• Concurrent active malignancy other than breast cancer
• Inability or unwillingness to comply with the planned follow-up and assessment schedule

Adult women with histologically confirmed Stage I-III breast cancer for whom neoadjuvant or adjuvant systemic therapy (chemotherapy and/or HER2-targeted therapy) is planned, recruited from the Medical Oncology outpatient clinic at Gazi University Faculty of Medicine Hospital, Ankara, Türkiye.

A formal IPD sharing plan has not yet been established. The study team will determine whether anonymized individual participant data can be made available upon reasonable request after study completion and publication, in accordance with applicable data protection regulations (including KVKK / GDPR), institutional policies, and ethics committee approval.