Abstract P1-18-34: Effectiveness of subcutaneous trastuzumab and intravenous pertuzumab as neoadjuvant dual blockade for locally advanced HER2 + breast cancer: Real world evidence from Instituto Oncologico Nacional, Panama City, Panama

Field: Medicine (Health Sciences)

Abstract Background: In Hannah trial subcutaneous (sc) trastuzumab showed an efficacy non-inferior to standard intravenous (iv) trastuzumab in Her 2+ breast cancer (BC). Dual blockade given iv has achieved improved pathologic complete response (pCR) when compared to therapies involving trastuzumab and chemotherapy but information on the efficacy of sc trastuzumab and iv pertuzumab is limited. In 2015 for administrative reasons our institution switched to sc trastuzumab so the aim of this study was to evaluate the effectiveness of sc trastuzumab and iv pertuzumab in neoadjuvant setting in our hospital. Methods: This was a retrospective, observational study in patients (pts) with HER2+ BC who received neoadjuvant therapy based on dual blockade with iv pertuzumab and sc trastuzumab since 2015 to 2018. All data were retrospectively collected from pts medical charts. The primary end point was pCR rate (ypT0/is ypN0). We used Chi square test to compare cualitative variables and non parametrics test for cuantiative variables and Kaplan Meier methods relapse free survival. Results: 182 pts received dual blockade (median age [range] 52.0 [22-82] years, stage II/III tumors 35/65%; median tumor size 5.5cm, 75% palpable lymph nodes, hormone receptor status positive/negative 54%/46%. 171 (94%) pts received taxanes+anthracyclines as chemotherapy. Breast-conserving surgery was performed in 17% and modified radical mastectomy in 83%. 2 pts refused surgery after dual blockeade. Pathological response was evaluated in 169 pts. pCR was 69.3% (n=108). According hormonal receptor status pCR was achieved by 74.6% (n=59) in hormone receptor-negative pts and 55.5% (n=50) hormone receptor-positive pts ( p=0.016). Diarrhea grade 2 was reported in 10% of pts, one pt died from toxicity (severe mucositis) during dual blockeade. 12 pts (6.5%) had EF decline ≥10% and 2 transient symptomatic heart faillure were reported. One patient had tumor progression during chemotherapy. The median time of follow up after surgery was 12 months 16 pts (8.7%) have relapsed. pCR was associate to lower relapse rate HR=0.22 (95% CI 0.06-0.79) Conclusions: Neoadjuvant pertuzumab and sc trastuzumab for HER2+ BC in the routine clinical practice setting in our institution enabled the achievement of total pCR rates over 69%, which are higher than those obtained in clinical trials. In addition, this therapy showed an acceptable safety profile. Citation Format: Omar Castillo-Fernandez, Franklin Castillero, Maria Lim, Cristiane Martin, Lilian Montano, Stephani Benitez, Jaime Samudio. Effectiveness of subcutaneous trastuzumab and intravenous pertuzumab as neoadjuvant dual blockade for locally advanced HER2 + breast cancer: Real world evidence from Instituto Oncologico Nacional, Panama City, Panama [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-34.