Education and cancer incidence and mortality: a prospective study of 0.5 million adults in the China Kadoorie Biobank

Thesis

Introduction: Socioeconomic status is an established risk factor for cancer; however, evidence from low- and middle-income countries remains limited. This thesis investigates the association of educational level, as a proxy of socioeconomic status, with overall and site-specific cancer incidence and mortality and the role of major risk factors as potential mediators of these associations using data from the China Kadoorie Biobank.

Methods: The China Kadoorie Biobank is a prospective cohort study of 512,724 Chinese adults aged 30–79 years, recruited in 2004-2008 from 10 rural and urban regions in China. Standardised overall and site-specific cancer incidence and mortality rates were estimated. Cox proportional hazards regression was used to estimate age- and region-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for cancer incidence and mortality by educational level. The percentage change in log relative risks was used to estimate the proportion of the associations explained by other socioeconomic characteristics and lifestyle factors.

Results: During 5,862,811 person-years of follow-up, 32,351 incident cancer cases and 16,913 deaths were registered. Lung cancer had the highest incidence of all cancers among both females and males. Among males, no formal schooling was associated with ~40% (HR 1.37, 95% CI 1.31-1.44) and ~70% (1.68, 1.58-1.77) higher risk of overall cancer incidence and mortality, while no significant trend was observed among females. The positive associations among males were driven largely by lung, stomach, liver, oesophagus and other upper aero-digestive tract cancers. Whereas among females, positive associations with lung, liver, and oesophageal cancers were off-set by inverse associations with breast and endometrial cancers. Other socioeconomic characteristics and lifestyle factors explained one-quarter to one-third of the educational inequalities in the risk of lung and gastrointestinal cancers among males. Among females, educational inequalities in breast cancer were mostly explained by other socioeconomic characteristics and childbearing factors.

Discussion: This thesis presents novel findings which describe substantial educational inequalities in site-specific cancer incidence and mortality in a large population-based cohort in China, which were partially explained by other socioeconomic characteristics and lifestyle factors. These findings could help inform public health policies and healthcare access to reduce cancer inequalities in China.

Authors: Elbasheer, M

• DOI: 10.5287/ora-zgee4nayw
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: socioeconomic inequalities; China Kadoorie Biobank; educational inequalities; cancer
• Subjects: Cancer Epidemiology