Overall survival of patients with de Novo HER2-positive metastatic breast cancer in the Netherlands from 2008 to 2017: A population-based cohort study of systemically treated patients

Aim: This study aims to determine whether real-world overall survival (OS) of patients with de Novo HER2-positive (HER2 +) metastatic breast cancer (MBC) in the Netherlands improved over time. Methods: Data of patients diagnosed with de Novo HER2 + MBC in 2008–2017 were retrieved from the Netherlands Cancer Registry. OS was estimated per two-year period using the Kaplan-Meier method and compared using the log-rank test for trend and the multivariable Cox proportional hazards analysis, adjusted for baseline characteristics and local therapy. First-given systemic and local therapy use was determined per two-year period. Results: Among 1458 patients included, 99 % (1452/1458) were female and 53 % (775/1458) aged 50–74 years at diagnosis. Comparing patients diagnosed with de Novo HER2 + MBC in 2008–2009 versus 2016–2017, the median OS improved from 30·9 months (95 %CI:25·0–35·4) to 57·3 months (95 %CI:46·7–68·1) (p-value for trend<0·001) (adjusted hazard rate ratio =0·49, 95 %CI:0·40–0·59). The use of any HER2-targeted therapy increased from 64 % (178/279) to 84 % (287/340), while the use of pertuzumab-based therapy increased from 0 % to 67 % (227/340) over the same period. The use of surgery remained stable over time, while radiotherapy use for both the primary tumour and metastases increased in recent years, from 16 % (44/279) and 15 % (42/279) in 2008–2009–22 % (76/340) and 26 % (88/340) in 2016–2017, respectively. Conclusion: OS has doubled over ten years, for patients diagnosed with de Novo HER2 + MBC in the Netherlands between 2008 and 2017. No change in metastatic presentation was observed over time, suggesting the improved OS is most likely explained by treatment improvements.