JMIR Publications

ABSTRACT

Background:

Adolescents and young adults (AYA, aged 15-39 years) with cancer represent a distinct epidemiological group with substantial social and economic implications. Asia bears the largest global AYA cancer burden, yet population-based evidence on incidence trends remains scarce and care models still draw largely from Western data. Singapore, a city state in Asia with a long-standing population-based cancer registry, offers a unique opportunity to characterise secular trends in AYA cancers.

Objective:

This study examined temporal trends in AYA cancer incidence in Singapore from 1968 to 2017. We hypothesised that overall incidence increased over time, with sex-, cancer type-, period-, and birth cohort-specific differences.

Methods:

Data on incident cancers (1968-2017) among AYA were obtained from the Singapore Cancer Registry and stratified by sex, five-year age group, and five-year period. Age-specific incidence rates (APSIR) and age-standardised incidence rates (ASIR) using the Segi-Doll world standard population were calculated. Joinpoint regression estimated annual percentage changes (APC) and average annual percentage changes (AAPC) to identify significant inflection points. Age-period-cohort modelling (APCm) assessed net drift and period- and cohort-specific rate ratios (PRRs, CRRs).

Results:

A total of 27,604 AYA cancer cases were identified. Females comprised 62.9% of cases, with incidence consistently exceeding that of males. Overall ASIR rose from 35.8 to 50.9 per 100,000 between 1968 and 2017 (+42.2%), with a steeper rise in females (39.1 to 64.1; +63.9%) than males (32.5 to 36.7; +12.9%). The most common cancers were nasopharyngeal carcinoma, lymphoid neoplasms, colorectal, myeloid, and testicular cancers in males, and breast, thyroid, ovarian, cervical, and lymphoid cancers in females. Cancer distribution shifted across the AYA age continuum, from haematological malignancies and sarcomas in younger adolescents to epithelial cancers (breast, thyroid, ovarian, and colorectal) in older AYAs. Joinpoint analysis identified a significant inflection in 2003, with APC accelerating from +0.5% to +2% per year (AAPC +0.8%). APCm showed significant net drifts in both sexes (+0.5% males, +1.2% females). Period effects were significant in females only, from 2003 onwards. Cohort-specific risks declined for nasopharyngeal carcinoma but rose for lymphoid neoplasms and testicular cancer among males, and for ovarian and lymphoid cancers among females, with cohorts born after the 1970s showing substantially higher risks and female cohort rate ratios peaking in those born in the 1990s.

Conclusions:

AYA cancer incidence in Singapore rose significantly over five decades, with a widening sex disparity likely driven by rising rates of breast, thyroid, ovarian, and lymphoid cancers among females. Significant cohort effects in both sexes and period effects specific to females suggest that generational shifts in risk factor exposures and calendar-time influences, amid Singapore's rapid economic and social development, have jointly shaped these trends. These findings contribute to the regional evidence base needed for AYA-specific prevention, early detection, and survivorship strategies.