Real-World Experience of HER2-Positive Advanced Breast Cancer (ABC) Treatment and Evaluation of Blood Biomarkers in a Public Institution in Latin America (LATAM).

Background: Advanced breast cancer (ABC) is an incurable disease, with a median overall survival (OS) of 3 years, even in high-income countries. Oncological treatment has improved survival rates, particularly for hormone receptor-positive and HER2-positive subtypes; however, access to new therapies in Latin American (LATAM) countries is limited.

Objectives: The impact of sequencing 2 lines of therapy in Peruvian patients with HER2-positive ABC in a single public institution was evaluated. First-line (1L) treatment consisted of trastuzumab and chemotherapy (CT, with taxanes), followed by second-line (2L) treatment with lapatinib plus capecitabine.

Design: In this retrospective study, we analyze clínico-pathological features (including blood biomarkers) collected from medical records of patients with HER2-positive ABC treated in a public Peruvian oncologic institution and its association with survival between 2020 and 2022.

Methods: Efficacy was measured using OS and progression-free survival (PFS). A discussion was added on the impact of OS based on clinicopathological characteristics, including outcomes in 2L "long-term responder" patients (who achieved response to 2L therapy ⩾6 months) and the evaluation of blood biomarkers.

Results: Treatment sequencing has been demonstrated to enhance OS in patients with HER2-positive ABC, with a median OS of 34 months. This effect is more pronounced among long-term responders (37 months), particularly those without central nervous system (CNS) involvement, as compared with those with CNS metastases (51 vs 34 months). Blood biomarkers were not found to be prognostic indicators for either PFS or OS.

Conclusions: Treatment sequencing has been demonstrated to enhance OS in LATAM patients with HER2-positive ABC. This study did not identify any prognostic blood biomarkers. These outcomes could influence the selection criteria for patients to receive treatment sequencing in countries without full access to innovative oncological therapies.