The goal of this observational study is to learn about the long-term effects of anthracycline chemotherapy on inflammation, oxidative stress, and heart function in adult women with breast cancer.

The main questions it aims to answer are:

1. Do inflammatory cytokine levels change after anthracycline chemotherapy and remain altered many years after treatment?
2. Are long-term markers of oxidative stress and antioxidant capacity associated with changes in heart structure or function after anthracycline exposure?

This study does not include a comparison group. All participants were previously treated with anthracycline-based chemotherapy as part of their standard cancer care.

Participants will:

1. Provide blood samples for the measurement of inflammatory cytokines and oxidative stress-related biomarkers
2. Undergo a clinical cardiovascular evaluation
3. Receive a transthoracic echocardiogram to assess heart function, including measures of systolic and diastolic function and myocardial deformation
4. Participate in a long-term follow-up assessment approximately 10 years after their initial cancer treatment

1. Study design and population. This is a prospective, observational translational study including adult patients with breast cancer undergoing anthracycline-based chemotherapy at a single tertiary-care center. Patients are evaluated longitudinally to assess subclinical cardiovascular alterations associated with anthracycline exposure. All participants are managed according to standard oncologic and cardiologic care pathways.

2. Echocardiographic assessment. Transthoracic echocardiography is performed by experienced cardiologists following current American Society of Echocardiography (ASE) recommendations. Studies are acquired at predefined time points, including baseline (prior to anthracycline exposure) and long-term follow-up. Left ventricular systolic function is assessed using biplane left ventricular ejection fraction (LVEF) calculated by the modified Simpson method. Diastolic function parameters include transmitral inflow velocities, tissue Doppler-derived mitral annular velocities, E/e' ratio, and left atrial volume index (LAVI).

   Left ventricular global longitudinal strain (GLS) is assessed at long-term follow-up using semi-automated speckle-tracking techniques. Right ventricular-pulmonary artery coupling is explored using the Tricuspid Annular Plane Systolic Excursion (TAPSE)/Pulmonary Artery Systolic Pressure (PASP) ratio. All measurements are performed offline, and segments with inadequate image quality are excluded from analysis.

3. Blood sample collection and processing. Peripheral venous blood samples are collected under standardized conditions at baseline (pre-anthracycline), early after chemotherapy exposure, and at long-term follow-up. Samples are obtained using chilled anticoagulant-containing tubes, centrifuged according to protocol, aliquoted, and stored at -80 °C until biochemical analyses are performed. All samples are processed under identical experimental conditions to minimize analytical variability.

4. Oxidative stress and antioxidant parameters. Plasma antioxidant capacity is assessed using the Ferric Reducing Ability of Plasma (FRAP) assay at predefined time points. Activities of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, are determined in erythrocyte lysates using commercially available assay kits according to manufacturers' instructions. Lipid peroxidation and intracellular redox status are evaluated using established biochemical methods. Results are normalized to protein concentration when applicable.

5. Inflammatory and proinflammatory cytokines. Circulating cytokines and growth factors are quantified in plasma samples using multiplex bead-based immunoassays. Measurements are performed at baseline and early after anthracycline exposure following standardized manufacturer protocols. Analyte concentrations are calculated based on standard curves generated for each biomarker.

6. Data integration and quality control. Clinical, echocardiographic, and biochemical data are collected using predefined case report forms. Data quality is ensured through consistency checks and verification procedures. All laboratory analyses and imaging measurements are performed blinded to clinical outcomes.

7. Exploratory analyses Echocardiographic parameters are integrated with biochemical markers of oxidative stress and inflammation for exploratory mechanistic analyses aimed at identifying associations between myocardial deformation indices and biological signatures of anthracycline-related cardiotoxicity.

Inclusion Criteria:

• Female patients with histologically confirmed breast cancer
• Age between 18 and 75 years
• Indication for anthracycline-based chemotherapy (>200 mg/m²)
• Eastern Cooperative Oncology Group (ECOG) performance status 0-2
• Written informed consent signed prior to study participation
• Availability for baseline cardiovascular and biomarker assessment and long-term follow-up

Exclusion Criteria:

• History of heart failure or left ventricular dysfunction (LVEF <53%)
• Known coronary artery disease or clinically significant ischemic heart disease
• History of clinically significant arrhythmias or requirement for antiarrhythmic therapy
• Dilated or hypertrophic cardiomyopathy
• Moderate to severe valvular heart disease (mitral or aortic stenosis or regurgitation)
• Congenital heart disease (including atrial or ventricular septal defects, patent ductus arteriosus, Ebstein anomaly, tetralogy of Fallot, coarctation of the aorta)
• Chronic kidney disease (creatinine >2 mg/dL)
• Hepatic failure (bilirubin >3 mg/dL, albumin <3.5 g/dL, or prothrombin activity <60% in absence of anticoagulation)

Adult women with breast cancer treated at Hospital del Salvador, Santiago, Chile. Patients were consecutively recruited between 2010 and 2013 from a prospective cohort of individuals initiating anthracycline-based chemotherapy. A protocol amendment approved by the local ethics committee allowed long-term follow-up of the original cohort at 10 years for cardiovascular, inflammatory, and oxidative stress assessment.