# Mortality Trends in Cancer of Unknown Primary Site in Serbia, 1990–2024: A Joinpoint Regression and Age–Period–Cohort Analysis

## TL;DR

This study analyzed cancer mortality trends in Serbia from 1990 to 2024, finding increasing rates in older adults and stable rates overall.

## Contribution

The study provides the first detailed analysis of mortality trends for cancer of unknown primary site in Serbia using joinpoint and age–period–cohort methods.

## Key findings

- Mortality rates for cancer of unknown primary site were stable overall but increased in those over 55 years old.
- Age–period–cohort analysis showed significant effects of period and cohort for males and cohort and period for females.
- The study highlights the growing public health concern of this cancer type among the elderly in Serbia.

## Abstract

Background/Objectives: Research on the mortality trends from cancer of unknown primary site in Serbia is scarce. This research sought to investigate temporal trends in mortality from cancer of unknown primary site in Serbia in the last few decades. Methods: This research was a population-based epidemiological descriptive study. Trends of age-standardized rates (ASRs) in mortality and average annual percent change (AAPC) were examined with joinpoint regression analysis. The age, period and cohort effects on mortality rates were evaluated using the age–period–cohort analysis. Results: From 1990 to 2024, 26,597 deaths from cancer of unknown primary site were registered in Serbia (14,944 in males and 11,613 in females). The trends for ASRs of mortality from cancer of unknown primary site in Serbia were stable for both males (AAPC = 0.2%, 95% CI = −0.4 to 0.7) and females (AAPC = 0.4%, 95% CI = −0.1 to 0.9) in all ages. Decreasing trends in mortality were observed in those under 55 years of age, while increasing trends were observed in older persons (55+), both in men and women. All estimated functions (period effect, cohort effect, the local drifts and net drift) for mortality in males in Serbia were significant (p < 0.05). For mortality in females, statistical significance was observed for cohort and period effects, along with the local drifts (p < 0.05 for all), while no statistical significance was observed for the net drift (p > 0.05). Conclusions: Mortality trends due to the cancer of unknown primary site were particularly unfavorable in elderly, suggesting that this burden of disease remains a public health issue in Serbia.