Regional and ethnic projections of gastric cancer incidence in Aotearoa New Zealand to 2045: identifying opportunities for targeted action.

BACKGROUND

Gastric cancer (stomach cancer) is an important contributor to morbidity and mortality in Aotearoa New Zealand, with marked ethnic inequities. Although national incidence rates are declining, Māori and Pacific peoples continue to experience higher rates than other groups. Demographic change and regional population growth are expected to influence future burden, yet no published projections provide estimates disaggregated by ethnicity and region.

METHODS

Gastric cancer registrations from 2001 to 2022 from the New Zealand Cancer Registry were linked to population estimates and projections stratified by age, sex, prioritised ethnicity and Health New Zealand - Te Whatu Ora region. Incidence was modelled using an age-period-cohort approach with time-based weighting to emphasise recent trends. Projections to 2045 were generated, and uncertainty was quantified using 1,000 non-parametric bootstrap iterations incorporating perturbation of population denominators.

RESULTS

Gastric cancer cases are projected to increase by 47.7% to approximately 725 per year by 2045, despite a decline in the age-standardised rate from 5.9 to 5.3 per 100,000. All regions show increasing absolute numbers, with the Northern Region experiencing the largest rise. Māori and Pacific peoples have the highest current incidence and a large proportional increase in projected cases, although incidence rates decline modestly for all ethnic groups. Future case growth is driven mainly by demographic expansion and an ageing population.

CONCLUSION

Absolute gastric cancer cases are projected to increase, particularly among Māori and Pacific populations and in regions experiencing rapid population growth. This has implications for early diagnosis and specialist service delivery. These projections support equity-focussed prevention and service planning, including Helicobacter pylori control, timely diagnostic pathways, and regional planning for specialist cancer services.