Socioeconomic inequalities in cancer survival: a population-based study of adult patients diagnosed in Osaka, Japan, during the period 1993-2004

Abstract

Background: Long-term recession of the Japanese economy during the 1990s led to growing social inequalities whilst health inequalities also appeared. The 2007 National Cancer Control Program of Japan targeted "equalisation of cancer medical services", but the system to monitor health inequalities was still inadequate. We aimed to measure socioeconomic inequalities in cancer survival in Japan.

Material and methods: We analysed 13 common invasive, primary, malignant tumours diagnosed from 1993 to 2004 and registered by the population-based Cancer Registry of Osaka Prefecture. An ecological socioeconomic deprivation index based on small area statistics, divided into quintile groups, was linked to patients according to their area of residence at the time of diagnosis. We estimated one-, five-year and conditional five-year net survival by sex, period of diagnosis (1993-1996/1997-2000/2001-2004) and deprivation group. Changes in survival over time, deprivation gap in survival, and change in deprivation gap were estimated at one and five years after diagnosis using variance-weighted least square regression.

Results: The deprivation gap in one-year net survival was narrower than in five-year net survival and conditional five-year survival. During the study period, there was no change in deprivation gap, except for reductions for pancreas (men) and stomach (women), and an increase for lung (men) in one-year survival. We observed a linear association between level of survival and deprivation gap at five years and conditional five years, but no association at one-year survival.

Conclusion: A wide deprivation gap in survival was observed in most of the adult, solid, malignant tumours, within the universal healthcare system in Japan. Overall, cancer survival improved in Osaka without any widening of inequalities in cancer survival in 1993-2004, shortly after the long-term economic recession and deep modifications in the social and work environments in Japan. The longer term impact of the recession on inequalities in cancer survival needs to be monitored using population-based cancer registry data.