Socioeconomic disparities in cancer survival: Relation to stage at diagnosis, treatment, and centralization of patients to accredited hospitals, 2005–2014, Japan

BACKGROUND: Cancer survival varies by socioeconomic status in Japan. We examined the extent to which survival disparities are explained by factors relevant to cancer control measures (promoting early‐stage detection, standardizing treatment, and centralizing patients to government‐accredited cancer hospitals [ACHs]). METHODS: From the Osaka Cancer Registry, patients diagnosed with solid malignant tumors during 2005–2014 and aged 15–84 years (N = 376,077) were classified into quartiles using the Area Deprivation Index (ADI). Trends in inequalities were assessed for potentially associated factors: early‐stage detection, treatment modality, and utilization of ACH (for first contact/diagnosis/treatment). 3‐year all‐cause survival was computed by the ADI quartile. Multivariable Cox regression models were used to assess survival disparities and their trends through a series of adjustment for the potentially associated factors. RESULTS: During 2005–2014, the most deprived ADI quartile had lower rates than the least deprived quartile for early‐stage detection (42.6% vs. 48.7%); receipt of surgery (58.1% vs. 64.1%); and utilization of ACH (83.5% vs. 88.4%). While rate differences decreased for receipt of surgery and utilization of ACH (Annual Percent Change = −3.2 and − 11.9, respectively) over time, it remained unchanged for early‐stage detection. During 2012–2014, the most deprived ADI quartile had lower 3‐year survival than the least deprived (59.0% vs. 69.4%) and higher mortality (Hazard Ratio [HR] = 1.32, adjusted for case‐mix): this attenuated with additional adjustment for stage at diagnosis (HR = 1.23); treatment modality (HR = 1.20); and utilization of ACH (HR = 1.19) CONCLUSIONS: Despite improvements in equalizing access to quality cancer care during 2005–2014, survival disparities remained. Interventions to reduce inequalities in early‐stage detection could ameliorate such gaps.