Abstract PO3-17-08: SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU

Abstract BACKGROUND: About 15% to 20% of breast cancers express positivity for human epidermal growth factor receptor 2 (HER2), a more aggressive breast cancer subtype with shorter survival. Trastuzumab, a humanized monoclonal antibody was approved by the U.S. Food and Drug Administration (FDA) for therapeutic use in metastatic breast cancer in 1998 and HER2-positive early breast cancer in 2006. HER2 overexpression is associated with more aggressive tumor growth and worse prognosis compared to HER2-negative tumors. HER2-positive tumors occur more frequently in younger women and node-positive women and are often less responsive to cytotoxic therapies. The primary objective of this study was to evaluate the tolerability of the subcutaneous formulation of trastuzumab in real life at the national institute of neoplastic diseases LIMA-PERU in patients with epidermal growth factor receptor 2 (HER2)-positive early breast cancer; efficacy was a secondary objective. METHOD: Female patients aged 18 years or older diagnosed between 2018-2019 with early epidermal growth factor receptor 2 (HER2)-positive breast cancer who received at least 1 dose of trastuzumab subcutaneously in a neo/adjuvant setting with or without chemotherapy were included. The treatment indication is 600 mg at a fixed dose every 3 weeks for 18 cycles. RESULTS: A total of 70 patients who received treatment with subcutaneous trastuzumab were included in the analysis. The mean age of the population was 52.6 ± 12.4 years, with the majority of patients being older than 50 years (54.29%). The mean number of subcutaneous trastuzumab cycles received was 11.4 ± 4.2. Adverse effects such as arthralgia (47.62%), diarrhea (9.52%), fatigue (9.52%) and injection site reaction (9.52%) occurred in 30% of patients. The mean number of cycles received until the first occurrence of adverse effects was 5.2 ± 2.1. It was observed that 97.14% completed treatment with trastuzumab subcutaneously, and 2.86% had to discontinue treatment. Cardiotoxicity and hypertension were the reasons why patients discontinued treatment. Of the patients included in the study, 63.77% received subcutaneous trastuzumab in the neoadjuvant setting, while the remaining 36.23% received it in the adjuvant setting. Of the patients, 45.71% started treatment with trastuzumab intravenously and received an average of 6 ± 3 cycles before switching to the subcutaneous presentation. After 3 years of follow-up, 7.14% developed disease progression; 57.1% had progression at the cerebral level, 28.6% at the local level and 14.3% at the pulmonary/hepatic level. 98.57% of patients are alive. CONCLUSIONS: In a real-life setting, subcutaneous trastuzumab is a well-tolerated and effective treatment option for patients even in patients who started treatment with the intravenous presentation and made the switch during treatment. Table 1: General clinical characteristics of patients XX XX Citation Format: Iris Otoya, Natalia Valdivieso, Zaida Morante, Carlos Castañeda, Silvia Neciosup, Mónica Calderón, Henry Gómez. SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-17-08.