Conditional Survival and the Choice of Conditioning Set for Patients With Colon Cancer: An Analysis of NSABP Trials C-03 Through C-07

Purpose Colon cancer overall survival (OS) is usually computed from the time of diagnosis. Survival gives the initial prognosis but does not reflect how prognosis changes with changing hazard rates over time. Conditional survival (probability of surviving y additional years given they have survived x years [CS or OS vertical bar OS]) is an alternative measure that accounts for elapsed time since diagnosis, providing more relevant prognostic information. We extend the concept of CS to condition on the set of patients alive, recurrence-free, and second primary cancer-free (disease-free survival [OS vertical bar DFS]). Patients and Methods Using data from National Surgical Adjuvant Breast and Bowel Project trials C-03 through C-07, 5-year OS vertical bar DFS was calculated on patients who were disease free up to 5 years after diagnosis, stratified by age, stage, nodal status, and performance status (PS). Results For stage II, OS vertical bar DFS improved from 87% to 92% at 5 years. For stage III, OS vertical bar DFS improved from 69% to 88%. Patients younger than 50 years showed OS vertical bar DFS improvement from 79% to 95%; those older than 70 years showed no sustained increase in OS vertical bar DFS. Node-negative patients with >= 12 nodes resected showed little change (89% to 94%); those with more than four positive nodes showed an improvement (57% to 86%). Patients with a PS of 0 or 1 demonstrated a small improvement; those with a PS of 2 did not (64% to 58%). Conclusion Prognosis improves over time for almost all groups of patients with colon cancer, especially those with positive nodes. OS vertical bar DFS is a more relevant measure of prognosis for those who have already survived disease free a period of time after diagnosis.