摘要：Objectives. We examined the differential effects of socioeconomic status on colon cancer care and survival in Toronto, Ontario, Canada, and San Francisco, California. Methods. We analyzed registry data for colon cancer patients from Ontario (n = 930) and California (n = 1014), diagnosed between 1996 and 2000 and followed until 2006, on stage, surgery, adjuvant chemotherapy, and survival. We obtained socioeconomic data for individuals’ residences from population censuses. Results. Income was directly associated with lymph node evaluation, chemotherapy, and survival in San Francisco but not in Toronto. High-income persons had better survival rates in San Francisco than in Toronto. After adjustment for stage, survival was better for low-income residents of Toronto than for those of San Francisco. Middle- to low-income patients were more likely to receive indicated chemotherapy in Toronto than in San Francisco. Conclusions. Socioeconomic factors appear to mediate colon cancer care in urban areas of the United States but not in Canada. Improvements are needed in screening, diagnostic investigations, and treatment access among low-income Americans. A study of cancer survival in low-income areas of Toronto, Ontario, and Detroit, Michigan, during the 1980s found advantages among Canadians for common cancers. 1 The Toronto survival advantage was replicated for breast cancer across diverse low-income Canadian and US contexts through the 1990s. 2 Studies of that era, however, were not able to account for differences in stage of disease at diagnosis. More recent studies that accounted for breast cancer stage again found Canadian advantages. 3 – 6 In the United States, women with breast cancer who lived in low-income areas waited longer for surgery and adjuvant radiation therapy and were less likely to receive radiation therapy or to survive. Similar disparities between high- and low-income women with breast cancer did not exist in Canada; thus low-income Canadians fared better across most breast cancer care indices than their US counterparts. More inclusive health insurance in Canada was advanced as the most plausible explanation. Colon cancer care may be an even more important health care performance indicator. The second most frequent cause of cancer death in North America, its prognosis can be excellent with early diagnosis and treatment. 7 , 8 For several reasons, colon cancer seems particularly instructive for Canada–US cancer care comparisons. First, research on income and colon cancer survival has found moderate to strong inverse associations in the United States but only modest to null associations in Canada. 1 , 9 – 13 Second, colon cancer screening is important, but implementation is at an early stage in both countries. 14 , 15 Third, effective chemotherapies proliferated during the 1990s for stage III colon cancer and more recently for stage II disease. 16 – 18 Fourth, screening, diagnosis, and treatment of colon cancer are more accessible to persons with higher socioeconomic status in the United States. 18 – 22 Colon cancer screening is more prevalent among higher-income persons in Canada, 23 but no previous study has examined associations of socioeconomic status with colon cancer treatment in that country. Because past studies have not observed associations between socioeconomic status and breast cancer treatment in Canada, 3 – 5 we hypothesized that we would also find no significant correlation. Previous comparisons of colon cancer survival in Canada and the United States showed a significant advantage for Canadians only for low-income and not for middle- or high-income patients. 1 , 9 , 24 These international studies of colon cancer survival, however, did not account for differences in stage at the time of diagnosis between countries, as ours did. Because of Canada's broad health insurance coverage, we expected to find an interaction between income and country for survival. We hypothesized that a direct income–survival gradient would exist in an urban California cohort but not in an urban Ontario cohort and that low-income persons in Ontario would have a survival advantage over those in urban California.
