Breast cancer mortality and screening mammography in New Zealand: Incidence-based and aggregate analyses

Abstract

Objective To investigate trends in breast cancer mortality in New Zealand women, to corroborate or negate a causal association with service screening mammography. Method Cumulated mortality rates from breast cancer deaths individually linked to incident cases diagnosed before and after screening commencement were compared, in women aged 50–64 (from 2001) and aged 45–49 and 65–69 (from 2006). Trends and differences in aggregate invasive breast cancer mortality (1975–2013) were assessed in relation to introduction of mammography screening targeting women aged 50–64 and 45–69. Joinpoint analysis was also undertaken. Results The reduction in incidence-based cumulated breast cancer mortality before and after the introduction of screening was −15% (p = 0.006) for women aged 45–69, and 17% (p = 0.005) for those aged 50–64. Aggregate mortality declined by −34% (2005–13 compared with 1992–98) in the age group 50–64, and by –28% among women aged 45–49 and –25% among women aged 65–74. For women aged 50–64 the 2-joinpoint model shows a 1990 turning point, from prior rising mortality to a mean −1.8% decline per annum, coinciding with improvements in primary treatment of breast cancer; and a steepening of the decline (−3.0% p.a.) from the late 1990s, coinciding with the introduction of service mammography screening. Conclusion Breast cancer mortality declines occurring since the advent of screening mammography in New Zealand are consistent with other incidence-based and aggregate studies of screening mammography in populations, individual-based cohort studies, and randomized controlled trials.