Characteristics and survival of de novo and recurrent metastatic breast cancer in New Zealand.

BACKGROUND We aim to examine the characteristics and survival of patients with de novo metastatic breast cancer (dnMBC) and recurrent metastatic breast cancer (rMBC) in New Zealand. METHODS This study included women diagnosed with dnMBC and women who developed rMBC between 2010 and 2017. The Kaplan-Meier method was used to examine cancer-specific survival. Cox proportional hazards regression was used to estimate the adjusted hazard ratio (HR) of cancer-specific mortality by ethnicity, age, year of diagnosis, socioeconomic deprivation, site of metastases, number of metastatic sites, biomarker subtype and MBC subgroup. RESULTS We included 2177 MBC patients (667 dnMBC and 1510 rMBC). The median survival of dn MBC patients was 26 months compared to 18 months for rMBC. There were no differences in breast-cancer specific mortality by ethnicity or socioeconomic deprivation. The adjusted HR for patients with visceral metastases compared to patients with non-visceral metastases was 1.41, and the adjusted HR for triple negative disease compared to Luminal A disease was 2.24. Compared to dnMBC, the adjusted HRs for rMBC patients with a metastatic-free interval of < 2 years, 2-4 years, 5-7 year and 8 + years were 1.81, 1.47, 1.08 and 0.82, respectively. CONCLUSIONS The survival for patients with MBC in New Zealand is very similar to other developed countries. Patients with dnMBC had a much better prognosis than those with recurrent disease. Patients with triple negative disease or non-luminal HER2 positive disease had the worst prognosis. The prognosis for patient with rMBC improved the longer the time from diagnosis to the development of metastases.