Influence of Income on Cancer Incidence and Death among Patients in Aomori, Japan

BACKGROUND: Aomori Prefecture has experienced the highest cancer-related mortality rates since the 2000s in Japan. In addition, income of residents in Aomori Prefecture is lower than that of a countrywide average. Aims of this study were to examine the relationships of the incidence and mortality rates of common cancers (stomach, colorectal, liver, lung, breast, cervical, and prostate) with the income levels of residential income area and clarify the factors contributing to the high mortality rates in Aomori prefecture. METHODS: We included data on all patients diagnosed with stomach, colorectal, liver, lung, breast, cervical, or prostate cancer in the Aomori cancer registry database between 2010 and 2012. Age-standardized incidence rates and incidence rate ratios were calculated. Risk of cancer mortality related to economic disparities was determined via multivariable Cox regression analysis and adjusted for age, sex, and stage at diagnosis in the multivariable model. RESULTS: We identified 21,240 eligible cancer patients. There were no differences in AIRs and IRRs among patients with stomach, colorectal, or lung cancer according to income. Contrarily, AIRs and IRRs were higher in higher-income areas than in lower-income areas among patients with breast, cervical, or prostate cancer. There were no significant differences in HRs according to income for any cancer type. CONCLUSIONS: Patients with higher income were diagnosed with early-stage disease more frequently, and they had higher AIRs for breast, cervical, and prostate cancers than those with middle and low incomes. However, there were no significant differences in hazard ratios.