Abstract P1-18-10: Preoperative treatment of HER2-positive breast cancer in South Sweden. A retrospective, comprehensive survey of neo-adjuvant treated HER2-positve breast cancer in the SCAN-B project 2010-2017

Introduction: Over the last few years, neoadjuvant therapy has become a standard of care in HER2-positive early breast cancer. This standard has recently been confirmed by the St. Gallen Consensus for stage II and III HER2-positive disease. In neoadjuvant treatment adding anti HER2 treatment almost doubled the pathological complete response (pCR) rate. Later studies have shown a better outcome for patients achieving a pCR compared with those with a non-pCR. The aim of this study is to present a comprehensive description of preoperative treatment in HER2-positive, according to ASCO and Swedish guidelines, breast cancer with detail treatment routines, choice of drugs and regimens as well as adherence to national guidelines and treatment changes over time. Material: During the period October 2010 to December 2017 6572 patients with early breast cancer were diagnosed in the Skåne region of South Sweden and included in the SCAN-B project (Sweden Cancerome Analysis Network - Breast project, ClinicalTrials.gov identifier NCT02306096). The SCAN-B project is a population based study that during the period included 76.7% of all primary breast cancer patients in the catchment area. The majority of all tumors have been analyzed by NGS-based RNA sequencing, RNAseq. Results: Of the 6572 patients 672 (10.2%) were HER2 positive and of these 101 (15%) were treated in a neoadjuvant setting with chemotherapy and HER2 directed antibodies. The proportion of HER2-positive patients receiving neoadjuvant treatment with trastuzumab increased from 9% in 2010 to 29% in 2017. Patient age was 27 to 89 years, median age 54 years. Pertuzumab was introduced in 2016 and in 2017 85% of patients received the combination of trastuzumab and pertuzumab. At diagnosis tumor stage T1, T2, T3 and T4d was 19%, 60%, 14% and 5% respectively and 50% were node negative at sentinel node biopsy pre treatment. Of tumors 52% were estrogen receptor positive (ie >10% stained nuclei). During the neoadjuvant treatment period 31 patients were hospitalized at median 2 times for toxicity and a total of medium 4.7 days. At surgery 62% had a mastectomy and 38% breast conserving surgery. Follow up time is median 3.9 years and overall survival 94%. Conclusions: This retrospective analysis of neoadjuvant treated HER2-positive breast cancer patients shows a gradual increase of neoadjuvant treatment and a very fast implementation of pertuzumab when it became available in Sweden. Overall survival is high but the follow up time is short and the material to small to analyze subgroups. Data on tumor RNAseq will be presented. Citation Format: Martin Malmberg, Christer Larsson, Johan Vallon-Christersson, Anna Ehinger, Cecilia Hegardt, Fredrika Killander, Lisa Ryden, Lao H. Saal, Niklas Loman, Åke Borg. Preoperative treatment of HER2-positive breast cancer in South Sweden. A retrospective, comprehensive survey of neo-adjuvant treated HER2-positve breast cancer in the SCAN-B project 2010-2017 [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 P1-18-10.