Association between socioeconomic status and cancer incidence in Toronto, Ontario: possible confounding of cancer mortality by incidence and survival.

Objective: To observe the association between socioeconomic status (SES) and cancer incidence in a cohort of Canadians.

Design: Cases of primary malignant cancer (83,666) that arose in metropolitan Toronto, Ont., from 1986 to 1993 were ascertained by the Ontario Cancer Registry and linked by residence at the time of diagnosis to a census-based measure of SES. Socioeconomic quintile areas were then compared by cancer incidence.

Results: Significant associations between SES and cancer incidence in the hypothesized direction--greater incidence in low-income areas--were observed for 15 of 23 cancer sites.

Conclusions: These findings, together with the recently observed consistent pattern of significant associations between SES and cancer survival in the United States and the equally consistent pattern of nonsignificant associations in Canada, support the notion that differences in cancer incidence alone explain the observed cancer mortality differentials by SES in Canada. The cancer mortality differential by SES observed in the United States is probably a function of differences in both incidence and length of survival, whereas in Canada such mortality differentials are more likely to be merely a function of differences in incidence by SES. This pattern of associations primarily implicates differences in the 2 health care systems; specifically, the more egalitarian access to preventive, investigative and therapeutic services available in the single-payer Canadian system.