Decline in the Incidence of Distant Recurrence of Breast Cancer: A Population-Based Health Record Linkage Study, Australia 2001-2016

Background: We investigated differences in cumulative incidence of first distant recurrence (DR) following non-metastatic breast cancer over a time period when new adjuvant therapies became available in Australia. Methods: We conducted a health record linkage study of females with localized (T1-3N0) or regional (T4 or N+) breast cancer in the New South Wales Cancer Registry in 2001 to 2002 and 2006 to 2007. We linked cancer registry records with administrative records from hospitals, dispensed medicines, radiotherapy services, and death registrations to estimate the 9-year cumulative incidence of DR and describe use of adjuvant treatment. Results: The study included 13,170 women (2001-2002 n = 6,338, 2006-2007 n = 6,832). The 9-year cumulative incidence of DR was 3.6% [95% confidence interval (CI), 2.3%-4.9%] lower for 2006-2007 diagnoses (15.0%) than 2001-2002 (18.6%). Differences in the annual hazard of DR between cohorts were largest in year two. DR incidence declined for localized and regional disease. Decline was largest for ages <40 years (absolute difference, 14.4%; 95% CI, 8.3%-20.6%), whereas their use of adjuvant chemotherapy (2001-2002 49%, 2006-2007 75%) and HER2-targeted therapy (2001-2002 0%, 2006-2007 16%) increased. DR did not decline for ages >= 70 years (absolute difference, 0.9%; 95% CI, -3.6%-1.8%) who had low use of adjuvant chemotherapy and HER2-targeted therapy. Conclusions: This whole-of-population study suggests that DR incidence declined over time. Decline was largest for younger ages, coinciding with changes to adjuvant breast cancer therapy. Impact: Study findings support the need for trials addressing questions relevant to older people and cancer registry surveillance of DR to inform cancer control programs.