Hidden inequalities in anal cancer mortality in Spain, 1999-2023: implications for targeted prevention

Anal cancer mortality has increased across high-income countries, yet subnational patterns remain poorly characterized. This study provides the first comprehensive, sex-stratified, spatiotemporal analysis of anal cancer (ICD-10 C21) mortality in Spain from 1999 to 2023.

We conducted an ecological, descriptive, province-level analysis of mortality using data from the National Institute of Statistics. Sex-stratified Bayesian hierarchical models were applied to estimate smoothed relative risks (RRs) by province and year, incorporating spatial, temporal, and interaction effects. Model selection was guided by the Deviance Information Criterion and Widely Applicable Information Criterion. Posterior probabilities (PP) were used to identify high-risk provinces (PP > 0.95).

Among 160 candidate models, optimal structures differed by sex: males showed intrinsic Conditional Autoregressive (iCAR) spatial prior with RW1 temporal prior and Type IV interaction; females showed iCAR with RW2 temporal prior and Type III interaction. Mortality rose in both sexes: male RR increased steadily to 1.39 in 2023; female RR followed a nonlinear trajectory with delayed surge to 1.30. Variance decomposition indicated male mortality was mainly temporal (80.2%), female mortality largely spatial (58.1%). Male hotspots clustered in southern/insular provinces (e.g., Las Palmas RR=1.22, Cádiz 1.18, Valencia 1.18); female hotspots were more dispersed (e.g., Las Palmas 1.34, Málaga 1.33, Barcelona 1.26).

Anal cancer mortality in Spain is rising, revealing persistent sex-specific and geographic inequalities beyond national temporal trends. Precision prevention-via gender-neutral HPV vaccination, targeted screening, and prioritization of hotspot provinces-is urgently needed.