Socioeconomic inequalities in colorectal cancer survival in England and Japan

Large improvements in cancer survival have been seen in the last two decades due to improvement in early diagnosis and treatment. However, inequalities in cancer survival remain, not only between but also within countries; survival varies by gender, age, ethnicity and socioeconomic status. Notably, socioeconomic inequalities in cancer survival were observed in England and part of Japan, despite healthcare systems based on universal health coverage. Particularly, colorectal cancer (CRC) has a wide range of variability in its survival by deprivation. For example, 3 to 10% difference in 1-year net survival for CRC between the least and the most deprived has been reported in both countries. However, the mechanisms of socioeconomic inequalities in cancer survival are still not fully understood. I examined whether socioeconomic inequalities in CRC treatment and survival existed in current data, and explored factors associated with the inequalities by investigating data from whole England and Osaka University Hospital in Japan. Firstly, I examined socioeconomic disparities in receipt of major surgery for the primary lesion and the postoperative mortality. Secondly, I examined the socioeconomic gap in CRC survival using flexible parametric models. Lastly, I proceeded to mediation analysis, a novel technique, to investigate the mechanism of survival inequalities. In England, socioeconomic inequalities in survival existed for both colon and rectal cancer in the stages of potential for cure. There were socioeconomic inequalities in receipt of surgery for rectal cancer, and in postoperative mortality for colon cancer in England. In Japan, no socioeconomic inequalities existed in receipt of major surgery and survival. Results of mediation analyses revealed that, in England, reducing emergency presentation for both colon and rectal cancer and improving postoperative care for colon cancer may reduce the survival inequalities. In Japan, further investigation with a larger population is needed to determine the survival inequalities and understand its mechanism.