Relative Survival and Trends in Patients with Prostate and Breast Cancers in Isfahan County, Iran, 2014–2021: A Population-Based Retrospective Cohort Study Using Join Point Regression

Abstract

Background and Objectives: Relative survival, as an estimate of net survival, is considered a more appropriate measure than observed survival or cause-specific survival for analyzing survival based on population-based cancer registry data. This study aimed to estimate and compare the relative survival of patients diagnosed with breast and prostate cancers in Isfahan County, Iran.

Methods: Data on patients with prostate cancer (n = 2,992) and breast cancer (n = 6,606) registered in the population-based cancer registry of Isfahan University of Medical Sciences between 2014 and 2021 were obtained from the Health Deputy of Isfahan University of Medical Sciences. Mortality data from the Finland population were used as the standard population to calculate expected survival. Relative survival was estimated by dividing observed survival by expected survival using R software. Temporal trends in survival over time were analyzed using Join Point regression software, and observed survival was calculated using Stata software.

Results: In both breast and prostate cancers, relative survival decreased with increasing age during the first three years of follow-up. In breast cancer patients, relative survival in 2018 was 3.14% higher in the age group ≥75 years compared to the 60–74 age group. In prostate cancer, relative survival was 0.782 with a 95% confidence interval (CI) of (0.75–0.81) in 2014, and increased with follow-up years, reaching 0.97 (95% CI: 0.908–1.30) in 2018. Join Point trend analysis showed that survival in both cancers had a downward slope in most age groups.

Conclusion: The study findings indicate that the observed changes in relative survival at older ages in breast and prostate cancers are likely due to the interaction of biological, clinical, and methodological factors. Therefore, age alone is not an independent prognostic indicator for cancer, and its interpretation requires consideration of other accompanying factors.