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.

Keywords: Breast cancer; New Zealand; mammography; mortality; service screening.