Abstract PO3-17-05: Clinical Characteristics and Outcomes of Patients Receiving Adjuvant Paclitaxel and Trastuzumab (APT regimen) for HER2-Positive Early-Stage Breast Cancer in Brazil: A Real-World Evidence

Abstract Introduction: The APT trial established adjuvant paclitaxel and trastuzumab (TH) as the standard of care for HER2-positive early-stage breast cancer with tumor size ≤ 3 cm and no more than one lymph-node micrometastasis. This single-arm phase II trial demonstrated favorable long-term outcomes, with a 3-year invasive disease-free survival (IDFS) rate of 98.7% (95% CI 97.6 – 99.8%). In an updated follow-up analysis, the 10-year IDFS and overall survival (OS) rates were 91.3% (95% CI 88.3 – 94.4%) and 94.3% (95% CI 91.8 – 98.3%), respectively. Nevertheless, outcomes observed in real-world scenarios have frequently been less favorable than those observed in clinical trials. We aimed to characterize the population receiving the APT regimen in clinical practice and evaluate if real-world outcomes align with those observed in the pivotal clinical trial. Methods: This retrospective cohort study included patients with HER2-positive early-stage breast cancer treated between 2015 and 2023 at four Brazilian cancer institutions, including public and private hospitals. Clinical and demographic data, treatment details, and outcomes were collected from electronic records. The primary endpoints were the 3-year and 7-year invasive disease-free survival (IDFS) rates. Secondary endpoints included overall survival (OS) and factors associated with IDFS. Survival analysis employed the Kaplan-Meier method, and Cox regression assessed prognostic factors. Results: A total of 133 patients treated with the APT regimen were evaluated, with a median age of 56 years (range 20–83). The majority had no special type breast carcinoma (92.4%), grade 2 (63.4%) or grade 3 (34.3%) tumors, no angiolymphatic invasion (76.3%), positive estrogen receptor (69.9%), positive progesterone receptor (55.6%), and node-negative disease (94.7%). Tumor staging distribution was as follows: T1a (12%), T1b (23.3%), T1c (49.6%), and T2 (13.5%). Most patients (95.4%) received the APT regimen as per guideline recommendations, while 3.8% received it due to contraindication to other therapies. With a median follow-up of 45.8 months, 8 patients (5.8%) experienced an invasive disease event or death from any cause: 5 (3.8%) had distant recurrence, 1 (0.8%) had local recurrence, and 2 (1.5%) died without recurrence. Notably, these events occurred in patients receiving the APT regimen according to standard indications, except for one patient with N+ disease and a contraindication to another regimen. The recurrence rate according to the T stage is presented in the Table. The 3-year IDFS rate was 100% (95% CI not applicable). All events occurred after the 3-year time point, resulting in a 7-year DFS rate of 80.8% (95% CI 62.7–90.7%). No prognostic factors related to IDFS were identified. Four patients died during the study period, yielding a 7-year OS rate of 88.0% (95% CI 61.6–96.6%). Conclusion: While the baseline characteristics of this cohort resembled those of the APT trial, the long-term outcomes observed in the real-world setting were less favorable. Further investigation is required to determine the reasons for this discrepancy, underscoring the necessity for larger real-world data studies to validate these findings. Recurrence rate according to T stage XX XX Citation Format: Giselle Carvalho, Renata Colombo Bonadio, Pedro Bergmann, Marina Nishimuni, André Rossi, Cristiano Souza, Gabriel Guimarães, Laura Testa, José Bines. Clinical Characteristics and Outcomes of Patients Receiving Adjuvant Paclitaxel and Trastuzumab (APT regimen) for HER2-Positive Early-Stage Breast Cancer in Brazil: A Real-World Evidence 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 PO3-17-05.