The narrowing sex gap in lip and oral cavity cancer incidence in Spain: Thirty years of divergent age-period-cohort trends.

BACKGROUND: Lip and oral cavity cancer (LOCC) accounts for a significant proportion of the overall burden of head and neck cancers, yet long-term sex-specific trends remain unclear. This study aimed to analyse sex-specific LOCC incidence trends in Spain from 1994 to 2023. METHODS: An ecological study was conducted using modelled incidence data from the Global Burden of Disease 2023 (GBD). Age-standardised incidence rates (ASIRs) were calculated using the European Standard Population. Joinpoint regression was used to estimate annual percent changes (APCs) and average annual percent changes (AAPCs). A-P-C modelling for ages 15-84 years was performed to estimate net and local drifts, and the effects of age, period and cohort. Analyses were stratified by sex. RESULTS: A total of 129,024 LOCC cases were identified, comprising 91,449 men and 37,575 women. Among men, the ASIR declined from 19.9 to 13.1 per 100,000 (AAPC: -1.6%), with a net drift of -3.0% per year. Cohort effects showed a marked reduction in risk across successive generations, whereas period effects declined steadily (rate ratio: 1.42-0.68). Among women, the ASIR increased from 4.0 to 6.5 per 100,000 (AAPC: 1.7%), with a net drift of 0.9% per year. Cohort effects plateaued among those born after 1960, whereas period effects increased (rate ratio: 0.92-1.13). Although incidence rose with age in both sexes between 1994 and 2023, the male-to-female gap narrowed substantially. CONCLUSION: LOCC incidence in Spain exhibits divergent sex-specific trends, driven by cohort and period effects in men and by period effects in women. The decline in rates among men is likely due to reduced tobacco exposure, while the increase among women may reflect the growing influence of alcohol consumption. These findings highlight the necessity for targeted, sex-specific prevention and early detection strategies.