Population-based trends in gastrointestinal cancer incidence and mortality in New Zealand: A 11-year analysis

Gastrointestinal (GI) cancers are a major contributor to the global cancer burden. However, no previous study has examined incidence and mortality across all GI cancer sites within a population, stratified by sex, ethnicity, and socioeconomic status. This retrospective, population-based study aimed to address this gap by providing a comprehensive overview of GI cancer incidence and mortality in New Zealand (NZ) from 2009 to 2019 and examining patterns across demographic subgroups. GI cancer cases (ICD-10-AM C15-C26) were identified from the NZ Cancer Registry and linked to the Mortality Collection to assess mortality. Baseline demographics were summarised, and age-standardised incidence and GI cancer-specific mortality rates were calculated. A total of 57,707 GI cancers were diagnosed in 55,611 individuals. The mean age at diagnosis and death were 69.9 (SD: 13.4) and 73.9 (SD: 12.9), respectively. Of those diagnosed with GI cancer, 54.4 % were male. Incidence trends varied by cancer site: small intestinal cancer increased annually (3 % in males, 4 % in females), while stomach and colorectal cancer incidence declined modestly for both sexes. GI cancer mortality declined significantly across all sites (males: RR=0.92;95 %CI:0.88,0.96;p = 0.002); females: RR= 0.91;95 %CI:0.87,0.96; p = 0.002). Māori and Pacific peoples had the highest incidence and mortality rates for stomach (incidence: 13.2 and 14.2; mortality: 9.3 and 7.1 per 100,000) and liver/biliary tract cancers (incidence: 14.1 and 18.1; mortality: 12.0 and 13.9 per 100,000). A clear socioeconomic gradient was observed, with higher incidence and mortality in the most deprived areas. This study reveals clear disparities in GI cancer incidence and mortality across sex, ethnic, and socioeconomic groups in NZ. These patterns highlight the importance of tailoring cancer prevention and early detection efforts to ensure they reach the communities most affected. A stronger focus on equity is needed, not just in NZ, but also in other settings where similar gaps in cancer outcomes persist.