Educational inequalities in site-specific cancer mortality: a Japanese census-linked study.

[BACKGROUND] Reports on socioeconomic inequalities in cancer mortality are limited in East Asia. We investigated educational inequalities in cancer mortality in Japan, serving as an advanced example of a nationwide census-based surveillance.

[METHODS] We developed a Japanese census-linked mortality dataset, using our unique linkage method. The dataset encompassed approximately 0.48 million cancer deaths linked to individual-level census data of 80 million Japanese aged 25-84 years in October 2020. We calculated age-standardised all-cancer and 23 site-specific cancer mortality rates (ASMRs) by educational level. Educational inequalities were quantified using the Relative Index of Inequality (RII) and Slope Index of Inequality (SII) by educational level (high, middle and low). Site-specific cancer contribution to absolute educational inequalities in all cancers was evaluated using the proportions of SII (%: SII/SII×100).

[RESULTS] All cancers' RIIs were 1.58 (95% CI 1.56 to 1.60) and 1.43 (1.40 to 1.46) in men and women, respectively. Among men, the rectum, stomach, liver and lung were the leading sites based on site-specific cancer RIIs, while the larynx, cervix uteri, liver and lung were the leading sites among women. In absolute terms, lung cancer contributed the most to educational inequalities, followed by stomach, colorectal and liver cancers. No educational inequality was found for pancreatic cancer. Breast cancer showed higher ASMRs among women with low education levels than among those with high education levels, which differed from the previous inequality pattern.

[CONCLUSIONS] Equity-focused strategies to enhance primary and secondary prevention are essential and should be supported by comprehensive nationwide monitoring.