Projected breast cancer incidence in Aotearoa New Zealand to 2045: national, regional and ethnic patterns with implications for equity and risk-based screening.

INTRODUCTION: Breast cancer is the most diagnosed cancer among women in Aotearoa New Zealand, with incidence rates among the highest globally. Māori and Pacific women experience higher mortality and later-stage diagnosis, reflecting more aggressive cancers, symptomatic detection and systemic barriers to care. Previous projections have not reported results by both ethnicity and region, limiting their use for regional planning.

METHODS: Female breast cancer incidence to 2045 was modelled using age-period-cohort Poisson regression, stratified by age, prioritised ethnicity and Health New Zealand - Te Whatu Ora region. Time weights were used to adjust for recent trends, and uncertainty was quantified using 1,000 bootstrap iterations incorporating variation in case counts and population estimates. Age-standardised incidence rates (ASRs) were calculated for observed and projected data.

RESULTS: By 2045, annual cases were projected to increase by 47% to 5,243, while the national ASR remained broadly stable at 98.6 per 100,000 (+3.4%). The Northern Region was projected to have the largest absolute increase (+55%), and Te Manawa Taki the largest rise in ASR (+8%). Māori and Pacific women were projected to continue having the highest incidence rates. Māori cases nearly doubled (+91%). Asian women experienced the largest proportional increase in case numbers (+215%), driven by population growth and ageing.

CONCLUSION: Breast cancer cases will increase substantially by 2045 despite stable national rates. Ongoing inequities for Māori and Pacific women and rising numbers among Asian women underscore the need for ethnically responsive screening and equity-focussed cancer control strategies. Risk-based approaches may improve detection and manage future screening demand.