Abstract PS5-04-14: Real-world cardiotoxicity in HER2-positive breast cancer patients in Peru

Abstract Background: Anti-HER2 therapies have significantly improved survival in HER2-positive breast cancer and are the standard of care. Early identification of Trastuzumab-related cardiotoxicity is essential to guide timely interventions and preserve cardiac function. While left ventricular ejection fraction (LVEF) remains the standard monitoring tool, it often misses subclinical dysfunction. Global longitudinal strain (GLS), derived from speckle-tracking echocardiography, offers greater sensitivity for early detection. Although Trastuzumab is used across Latin America, published data on cardiotoxicity remain limited. This study analyzes cardiotoxicity prevalence and evaluates the role of LVEF and GLS in cardiac surveillance in a real-world Peruvian cohort. Methods: We performed a retrospective observational study among 144 women diagnosed with HER2-positive breast cancer who were treated with Trastuzumab ± Pertuzumab in adjuvant, neoadjuvant, or metastatic settings. Clinical-pathological variables and patterns of treatment were collected. Cardiac function was assessed using electrocardiogram (EKG), serum troponins, echocardiographic measurements of LVEF, and GLS at baseline, during and at treatment completion. Cardiotoxicity was defined as either a ≥10% absolute reduction in LVEF or a ≥15% absolute reduction in GLS. Results: The median age was 49 years (range 24-73). Of the total cohort, 112 patients received neoadjuvant treatment, 93 continued with adjuvant therapy, and 37 were treated for metastatic disease. Left-sided radiotherapy was administered in 28% of cases. Pertuzumab was co-administered in 39% of patients. The median number of Trastuzumab cycles was 15, over a median treatment duration of 45 weeks. Median dose density was 0.33 doses/week for Trastuzumab and 0.23 doses/week for Pertuzumab. All patients underwent baseline electrocardiogram and troponin assessment. Except for one case of chemotherapy-related tachyarrhythmia, all patients were asymptomatic throughout treatment. LVEF measurements were available in 136 patients (94.4%) and GLS in 118 patients (81.9%). Cardiotoxicity was observed in 12 patients (8.3%): 9 patients experienced a ≥10% reduction in LVEF and 3 experienced a ≥15% reduction in GLS, with no overlap between the two groups. Subgroup analysis showed that all GLS alterations occurred in neoadjuvant patients, while LVEF reductions were observed in 4 neoadjuvant, 1 adjuvant, and 4 metastatic cases. Among those with LVEF decline, 2 were obese and 2 had received left-sided radiotherapy. Among GLS-declining patients, 1 had also received left-sided radiotherapy. One patient with GLS decline also presented with elevated troponin, suggesting subclinical myocardial injury. Conclusions: Cardiotoxicity affected 8.3% of patients in this Peruvian real-world cohort, with no overlap between LVEF and GLS-defined events. GLS enabled detection of subclinical myocardial dysfunction not identified by LVEF. The presence of known risk factors such as obesity and left-sided radiotherapy in several cases underscores the need for comprehensive cardiac monitoring. These findings support the integration of GLS into routine surveillance, particularly for high-risk patients, to enable early cardioprotective interventions and ensure continuity of oncologic treatment. Citation Format: J. Sanchez A, W. Cruz-Diaz, J. Luque, V. Tuesta, E. Ruiz-Mori, Z. Morante, G. Valencia, P. Rioja, S. Neciosup, T. Vidaurre, K. Roque, C. Castañeda. Real-world cardiotoxicity in HER2-positive breast cancer patients in Peru [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-04-14.