Characteristics and post-metastasis survival of recurrent metastatic breast cancer over time - An Australian population-based record linkage study, 2001-2016

To assess population-level characteristics and post-metastasis survival of people with recurrent metastatic breast cancer (rMBC) during a period when new publicly-subsidised adjuvant and metastatic systemic therapies became available. Record linkage study of females in NSW Cancer Registry (NSWCR) diagnosed with non-metastatic breast cancer (BC) in 2001-2002 (C1) and 2006-2007 (C2). We identified first rMBC from NSWCR, administrative hospital records, dispensed medicines and radiotherapy services (2001-2016). We used death registrations to estimate cumulative incidence of BC death. The analysis included 2267 women with rMBC (C1:1210, C2:1057). Compared to C1, C2 had access to adjuvant HER2-targeted therapy and were more likely to have received adjuvant chemotherapy (C1:38%, C2:47%) and aromatase inhibitors (C1:52%, C2:73%, of those dispensed endocrine therapy). Five-year probability of BC death was 65% (95%CI:62-68%) in C1 and 63% (95%CI:60-66%) in C2. Regional disease (T4 or N + ) at initial BC diagnosis (C1:62%, C2:68%), and age ≥ 70 years at first metastasis (C1:27%, C2:31%) were more common in C2 and had poorer prognosis. Five-year probability of BC death was lower in C2 than C1 for treatment-defined HER2-positive BC (C1:72% 95%CI:63-79%; C2:52% 95%CI 45-60%) and those dispensed chemotherapy alone (C1:76% 95%CI:69-82, C2:67% 95%CI:59-74%, p = 0.01), but not treatment-defined hormone receptor-positive HER2-negative BC (C1:60% 95%CI 56-63%, C2:64% 95%CI 60-68%). Despite less favourable prognostic characteristics in C2, BC-related survival following rMBC was similar between the two cohorts; and improved for women with HER2-positive tumours. These findings support the real-world benefits of newer treatments for rMBC.