Response criteria and statistical analysis. Response to treatment was assessed according to the International Working Group Recommendations for Response Criteria for NHL [25, 26] . OS was calculated from the date of diagnosis to the date of death from any cause or to the date of last followup. Clinical characteristics of PPL cases were summarized by means, medians, and percentages, and were compared using the g 2 or Fisher's exact test. The primary endpoint of our analysis was OS. Survival curves were analyzed using the Kaplan-Meier method. The prognostic importance of different variables in OS was estimated by multivariate analysis using the Cox regression model. A two-tailed P < 0.05 assessed by the log-rank test was considered statistically significant. Statistical analysis was performed using SPSS 16.0 for Windows. 