Trastuzumab biosimilars interchangeability: Preliminary real-world data in neoadjuvant breast cancer setting.

e23305 Background: Interchangeability (IC) among biosimilar compounds is still an issue not completely addressed, due to concerns on adverse events, immunogenicity, and efficacy. Many regulatory agencies around the world have adopted IC aside of appropriate clinical trials evaluation. Brazil’s Public Health System (SUS) has centrally provided trastuzumab (T) for breast cancer (BC) and firstly adopted biosimilars in 2020, after their regulatory approval 2 years before. After T biossimilar adoption there was an improvement of access for its all clinical indications, however different compounds had been offered to patients (pts) along their treatment. The aim of this study is evaluating the impact of these exchanges of types of T on patient-based registry. Methods: We reviewed all pharma and clinical data between 2020 and 2022 from all pts, stage III, Her2-Positive, who received neoadjuvant treatment based on chemotherapy plus trastuzumab in a Comprehensive Cancer Center in Southern Brazil. The main objective is measuring the rates of changes among T biosimilar compounds, and its impact in pathological response (pCR), toxicity and treatment-failure rates. Chi-square, Fisher’s Exact, t-test, or Mann-Whitney testing, as appropriate, was used to compare events between groups. Results: Along the studied period, SUS had offered 3 T biosimilars: ABP 980 (Amgen), CT-P6 (Celltrion), SB3 (Samsung), plus reference trastuzumab (Roche). The standard regimen was ACq21 4cycles followed by Taxane (Docetaxel q21 or weekly Paclitaxel) plus T 4cycles. 146 pts were eligible to analysis. 83 pts received only one type of T compound (non-interchangeability group – NICG), 63 pts received at least 2 different T compounds along the treatment (Interchangeability Group – ICG). Both groups were comparable in terms of clinical features (age, ER/PR status, menopausal status, PS, tumor size, and staging of axillary lymph nodes). Rate of IC along the time was 11%, 53% and 33% in 2020, 2021 and 2022, respectively. pCR was 32,5% in NICG versus 33,3% in ICG (p:NS). In total, 3pts had their treatments interrupted due to toxicity (1pt cardiac, 2pts hematologic). Conclusions: Although IC among biosimilars compound had been globally accepted, it was not clinically fully tested. Brazilian Ministry of Health, as the only provider, has a policy based on lowest cost for trastuzumab compound, causing constant changes along pts treatments. Furthermore, it is expected that Brazil has the potential to evaluate the IC in thousands of pts prospectively next years. Hereby, we could demonstrate preliminary based on retrospective data that exchange among different biosimilar compounds did not interfere significantly on pCR, nor raised any new safety or clinical concerns.