Further enhanced monitoring of cancer patient survival by stage-adjusted period analysis

Monitoring progress in cancer patient survival is an important task of population-based cancer registration. Period analysis has been shown to provide more up-to-date estimates of cancer patient survival than traditional methods of survival analysis. However, even period estimates may disclose recent improvements in long-term survival with some delay as they are still partly based on the survival experience of patients diagnosed years ago. If these patients had a less favorable stage distribution than the patients diagnosed in a more recent calendar period (e.g., due to progress in early detection), period estimates may underestimate long-term survival for patients diagnosed in that period. This particular source of potential underestimation can be overcome by adjustment of the stage distribution of all patients included in period analysis to the stage distribution of the patients diagnosed in the period of interest. The principle, application, and use of stage adjustment of period survival estimates are illustrated with 5- and 10-year relative survival estimates of patients diagnosed with breast cancer and followed with respect to survival in the United States between 1973 and 2001, using data of the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute. We show that stage adjustment may often further enhance the benefits of period analysis for deriving up-to-date cancer survival estimates.