A proportional regression model for 20 year survival of colon cancer in Norway.

Twenty year survival of all Norwegians with colon cancer registered in a period of 10 years is estimated by both relative survival rates, and with a proportional regression model for the excess intensity. Male colon cancer patients have a significant positive excess mortality at least 20 years after diagnosis, while the excess mortality for females is about zero after 10 years. Stratified analyses for men indicate non-proportionality throughout the follow-up period, and when this information is included in the regression model, there are significant effects of age between 60 and 70 years and for pelvic cancer. The use of proportional regression models is also discussed when excess intensities are close to zero or negative.