Use and results of systemic treatments for de novo and recurrent metastatic breast cancer: a population-based cohort study.

ABSTRACT

AIMS: To describe the systemic treatments in patients with de novo metastatic breast cancer (dnMBC, initial metastatic diagnosis) and recurrent metastatic breast cancer (rMBC). METHODS: Women diagnosed with dnMBC and rMBC in 2010-2017 were identified. Adjusted odds ratios of receiving systemic treatments were estimated by logistic regression model. Cox proportional hazards regression was used to estimate adjusted hazard ratio of breast cancer-specific mortality by treatments. RESULTS: The adjusted odds ratio of having chemotherapy and trastuzumab (for human epidermal growth factor receptor 2 positive (HER2+) disease) for Pacific women was 0.43 and 0.13 compared to European women. Patients receiving chemotherapy had improved survival for HER2+ non-luminal and triple negative metastatic breast cancer (MBC) (hazard ratios 0.30, 0.66). Those with endocrine therapy was associated with better survival for luminal A and luminal B HER2+ MBC (hazard ratio 0.25, 0.26). Trastuzumab was associated with superior survival in luminal B HER2+ and HER2+ non-luminal disease (hazard ratio 0.34, 0.40). CONCLUSIONS: Pacific women with MBC were less likely to receive chemotherapy and trastuzumab than non-Pacific women. Chemotherapy was associated with improved survival in HER2+ non-luminal and triple negative MBC. Endocrine therapy improved survival in luminal A and luminal B HER2+ disease. Trastuzumab was associated with improved survival in luminal B HER2+ and HER2+ non-luminal disease.