Abstract P1-14-06: Long-term treatment patterns and OS in metastatic breast cancer by intrinsic subtypes in a clinical setting in Sweden
Authors: Lindman H , Sjöberg F , Wiklund F , Christensen HN 
Published: May 2019

Abstract
Background
Breast cancer is the most common female cancer in Sweden, and patients diagnosed with early stage have a good curative prognosis. However, once metastases are detected, the disease is incurable. There is lack of detailed knowledge on the current management of metastatic breast cancer (MBC), especially treatment lines beyond second or third line. The aim was to describe long-term treatment sequences and OS for metastatic breast cancer patients by intrinsic subtypes in a clinical setting in Sweden.
Method
In this observational cohort study, women with MBC treated between 2009-2017 were identified in the RealQ® clinical database (Uppsala University Hospital, Sweden). Clinical characteristics, complete MBC treatment regimens, and overall survival (OS) were obtained. Patients were classified into intrinsic subtypes as determined by gene expression profiling i.e., luminal A, luminal B, HER2 subtype, and basal-like (also called triple negative breast cancer [TNBC]). OS was defined from date of first metastatic diagnosis until date of death, migration or end of study. Survival rates were estimated using the Kaplan-Meier method. Subgroup analyses among deceased patients were conducted for all treatment lines and combinations. Treatment exposure rates for each treatment category were calculated using the following formula: exposure rate = person-years for the treatment category/total person-years × 100.
Results
The full analysis set comprised 371 MBC patients (mean age 67 years, 88% with performance status 0 or 1) of which 350 patients could be subtyped: 118 (34%) Luminal A, 119 (34%) Luminal B, 68 (19%) HER2, and 45 (13%) TNBC. Median follow-up was 27 months and median OS was 32.5 months; 5-year survival rates for Luminal A,Luminal B,HER2, and TNBC were 27%, 29%, 36%, and 7%, respectively. In total 245 patients died during the observation period. The deceased patients had been treated with mean 4.5 lines (median 4, range 1-18), mean time from last treatment to death was 5.4 weeks (median 0, range 0-224). Luminal B patients (n=79) were younger (mean age 66.4 vs. 70.7 years), had more often 2+ metastatic sites (64.6% vs. 57.8%) and visceral as primary metastatic location (69.6% vs. 60.2%) compared with Luminal A patients (n=83). Generally, Luminal B patients were treated with chemotherapy more frequently than Luminal A patients, and chemotherapy was more often at later treatment lines. Total exposure rate for all chemotherapy were 33.6% among Luminal B patients vs. 24.1% among Luminal A patients (p=0.03), and for all endocrine therapy 49.4% among Luminal B patients vs. 61.9% among Luminal A patients (p=0.02). There was no difference in mortality for Luminal B and A patients when adjusting for age, number of metastatic sites, visceral metastatic location, and treatment (p&gt;0.05).
Conclusion
This observational study of MBC patients in clinical practice shows relatively short OS despite an extensive management with numerous treatment lines and combination therapies. Regardless of differences in treatment patterns for Luminal A and B patients the long-term OS was similar for these patient groups, highlighting the importance of awareness and careful consideration in management of MBC beyond second or third treatment line.
Citation Format: Lindman H, Sjöberg F, Wiklund F, Christensen HN. Long-term treatment patterns and OS in metastatic breast cancer by intrinsic subtypes in a clinical setting in Sweden [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-14-06.