Temporal trends in the association between socioeconomic status and cancer survival in Ontario: a population-based retrospective study.

BACKGROUND

Cancer survival is known to be associated with socioeconomic status. The income gap between the richer and poorer segments of the population has widened over the last 20 years in Canada. The purpose of this study was to investigate temporal trends in disparities in cancer-specific survival related to socioeconomic status in Ontario.

METHODS

There were 920 334 cancer cases between 1993 and 2009 in the Ontario Cancer Registry. We linked median household income from the Canadian census to the registry. We calculated 5-year cancer-specific survival rates for all cancers combined and for specific cancer sites by socioeconomic status quintile and year of diagnosis, and modelled time to death using Cox regression.

RESULTS

Between 1993 and 2009, for all cancers combined, the hazard of death decreased by 3.1% (hazard ratio [HR] 0.969 [95% confidence interval (CI) 0.967-0.971]) per year in the richest quintile and by 1.2% (HR 0.988 [95% CI 0.987-0.990]) per year in the poorest quintile. The corresponding values for breast cancer were 4.3% (HR 0.957 [95% CI 0.951-0.964]) and 2.0% (HR 0.980 [95% CI 0.975-0.986]); for lung cancer, 1.4% (HR 0.986 [95% CI 0.982-0.990]) and 0.3% (HR 0.997 [95% CI 0.995-1.000]); for colorectal cancer, 3.7% (HR 0.963 [95% CI 0.958-0.968]) and 1.8% (HR 0.982 [95% CI 0.978-0.985]); and for head and neck cancer, 3.1% (HR 0.969 [95% CI 0.958-0.979]) and 1.0% (HR 0.990 [95% CI 0.983-0.996]).

INTERPRETATION

Between 1993 and 2009, cancer-specific survival in Ontario improved more among patients from affluent communities than among those from poorer communities. This phenomenon cannot be explained by increased disparity in income.