Survival rates for four forms of cancer in the United States and Ontario

Objectives: In this study, cancer survival rates for patients diagnosed in Ontario and selected areas within the United States were compared. Methods: Relative survival rates were computed for patients aged 15 through 84 years diagnosed with any of four forms of cancer (breast, colon, lung, and Hodgkin's disease). The cohorts represented those diagnosed over the years 1978 through 1986 in the Canadian province of Ontario and in nine regions covered by the US National Cancer Institute's Surveillance Epidemiology and End Results program. Patients were followed through the end of 1990. Results: The cumulative relative survival rates were similar for American and Canadian patients. The largest difference was observed for breast cancer, where patients in the United States enjoyed a survival advantage throughout the follow-up period. Conclusions: Patients in the United States and Ontario with the diseases studied, except for breast cancer, experience very similar survival. The greater use of mammographic screening in the United States could account for that country's higher breast cancer survival rate by promoting earlier and therefore more efficacious treatment, by introducing bias, or by a combination of both treatment and bias factors.