Abstract P2-08-06: Initial systemic treatment choices by subtype of advanced breast cancer in 2007-2017, a study of the southeast Netherlands advanced breast cancer (SONABRE) registry

Background The aim of this study was to determine the subtype conversion rate and the initial systemic treatment choices by subtype for patients diagnosed with advanced breast cancer since 2007 who were included in the SONABRE Registry. Patients and methods Patients diagnosed with advanced breast cancer in 2007-2017 in six (one academic, three teaching, two non-teaching) hospitals in the Netherlands were selected from the ongoing SOutheast Netherlands Advanced BREast Cancer (SONABRE) Registry (NCT-03577197). We registered patient, primary tumor, recurrent and metastatic disease characteristics, and (neo-)adjuvant and palliative treatment choices. Follow-up was collected until September 2018. To determine the subtype, we assessed the hormone receptor (HR) and the human epidermal growth factor receptor (HER)-2 status from the initial metastatic site(s). If not available, biopsy results from the locoregional recurrence or the primary breast cancer were used. Initial systemic treatment choices were presented by subtype (HR+/HER2-, HER2+, and triple negative (TN) disease). In this abstract, we present the findings for the period 2007-2017, at the SABCS 2019, we will present the results for the period 2007-2018. Results Of the 2288 patients included, 67% had HR+/HER2-, 16% HER2+, 15% TN disease and 2% of patients had unknown subtype. The HR and HER2 status were based on pathology of the metastasis in 48% and 40% of patients, respectively. In 41% and 25% of patients, the HR and HER2 status was determined for both the primary tumor and the initial metastatic sites. Of these latter patients, HR status changed from HR+ to HR- in 10% of patients and from HR- to HR+ in 2% of patients. HER2 status changed from HER2+ to HER2- in 6% of patients and from HER2- to HER2+ in 4% of patients. Among patients with HR+/HER2- disease, 78% received endocrine-based and 17% received chemotherapy-based therapy as initial systemic therapy, and 5% of patients deceased without receiving any systemic therapy. For patients with HER2+ disease, 57% received HER2-targeted based therapy as initial systemic treatment, 22% received endocrine monotherapy, 8% received chemotherapy alone and 13% deceased without receiving systemic therapy. In patients with TN disease, 71% received chemotherapy as initial systemic treatment, 4% received endocrine therapy and 25% received no systemic therapy. Overall, 6% of patients received initial systemic therapy as part of a clinical trial. Conclusions For only half of the patients, HR and HER2 receptor status of the metastasis were determined at initiation of initial systemic therapy. Since one in ten tested patients showed a conversion of subtype, and thus impacting treatment decisions, it is important to reassess subtype upon diagnosis of metastatic disease whenever possible. With a few exceptions, initial systemic treatment choices were in line with guideline recommendations. Only 6% of patients were treated as part of a clinical trial, confirming the highly selected patient population included in these trials, highlighting the importance of real life studies to evaluate the outcomes of systemic treatment for advanced breast cancer. Citation Format: Sandra M.E. Geurts, Khava IE Ibragimova, Frans Erdkamp, Birgit EPJ Vriens, M. Wouter Dercksen, Marien O den Boer, Manon JAE Pepels, Dominique Tilli, Maaike de Boer, Vivianne CG Tjan-Heijnen. Initial systemic treatment choices by subtype of advanced breast cancer in 2007-2017, a study of the southeast Netherlands advanced breast cancer (SONABRE) registry [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 P2-08-06.