Rising mortality from small intestinal cancer in Spain, 1999-2023: joinpoint and age-period-cohort analysis

Small intestinal cancer is a rare neoplasm whose mortality has been increasing in several high‑income countries, yet long‑term patterns in Spain remain poorly described.

This study aims to analyse temporal trends and decompose the effects of age, period, and birth cohort on small intestinal cancer mortality in Spain between 1999 and 2023.

A population-based time-series study was conducted using national mortality data from the National Statistics Institute. Age-standardized mortality rates (ASMR) were calculated using the 2013 European Standard Population. Joinpoint regression was used to identify significant trend changes, and age-period-cohort modelling was applied to quantify the contributions of biological aging, calendar period, and generational effects.

Between 1999 and 2023, the ASMR rose significantly in men (0.43 to 0.81 per 100,000; average annual percentage change: 2.1%) and more modestly in women (0.30 to 0.38 per 100,000; AAPC: 1.1%). The increase was driven almost entirely by individuals aged 50 years and older, while rates in those under 50 remained low and stable. Age-period-cohort analysis revealed a significant net drift (1.07% per year) and strong birth cohort effects in men, with mortality risk increasing for successive generations born through the mid-20th century. In women, the rise was primarily attributed to the age effect.

Small intestinal cancer mortality in Spain is increasing, particularly among men and older age groups. The significant cohort effect in men suggests that shifting environmental or lifestyle exposures are contributing to the growing burden of this malignancy.