Time to disease progression dichotomized by cluster groupings. Kaplan-Meier analysis demonstrates that patients in cluster group 2 (- - -) had a shorter time to disease progression after fludarabine therapy compared with those in cluster group 1 (—). The difference is significant, with a hazard ratio of 3.4 (P = .058 by log-rank analysis). The hazard ratio is 3.97 (P = .0081 using Cox regression).