Platelet Count Is an IPSS-Independent Risk Factor Predicting Survival in Refractory Anemia with Ringed Sideroblasts.

Abstract

Background: We sought to validate the International Prognostic Scoring System (IPSS) for myelodysplastic syndromes (MDS) in a well-characterized group of patients with refractory anemia with ringed sideroblasts (RARS), as well as to assess the validity of novel and easily obtained prognostic factors such as complete blood count (CBC) parameters. For instance, Bowles and colleagues (Br J Haematol 2006; 135: 198) recently reported that a low platelet mass (i.e., mean platelet volume (MPV) x platelet count <0.60 mL/L) is a marker for poor survival (median, 5 months) in patients with MDS, and also asserted the MPV and platelet count do not correlate so the MPV provides independent prognostic information. Because platelet parameters have been of particular interest in RARS, especially with respect to the provisional entity RARS with thrombocytosis (RARS-T), we assessed the prognostic relevance of MPV and platelet count/mass in this MDS subtype.Methods: We analyzed all pts diagnosed with RARS by FAB criteria at Mayo Clinic between 1994 and 2002, a period chosen because it was the interval when the MPV was routinely reported along with CBCs at our center. We excluded pts who were evaluated at Mayo Clinic >6 months after initial diagnosis or were being treated for other malignancies (e.g., lymphoma or myeloma). Medical records, blood parameters, bone marrow findings, and cytogenetic results were reviewed. We performed time-to-event analysis using Kaplan-Meier estimates and Cox proportional hazards modelling, with Chi-Square statistics to assess significance (i.e., type I error rate <0.05).Results: A total of 127 pts (79 males; median age 73 years, range 51-90) were identified, with 78 verified events during the follow-up period. The median survival was 3.9 years. The correlation between MPV and platelet count was poor (Pearson correlation coefficient, -0.18). Platelet count was low in 26 pts, within the normal range in 93 pts, and elevated in 8 pts (but >600 ×109/L in only 2). In univariate analysis, lower Hb, lower MCV (but not MPV), higher total white count, lower platelet count, abnormal cytogenetics, and higher IPSS score each predicted poorer survival. In multivariate analysis using a proportional hazards model, only the platelet count (hazard ratio 0.93 for each increase in count by 25, 95% confidence interval (CI) 0.88-0.98, p=0.0055) and IPSS score (hazard ratio 7.7 for each increase in IPSS score by 1, 95% CI 4.1-14.4, p<0.0001) remained independently predictive of survival. Relatively few patients with RARS have either low platelet mass (<0.60 mL/L, 8%) or intermediate platelet mass (0.60-1.20 ml/L, 12%) as defined by Bowles et al. While the platelet mass was indeed predictive of survival (p<0.0001), this was due entirely to the platelet count, and there was no additional information from the MPV.Conclusion: The IPSS is an excellent predictor of survival in pts with RARS, and the quantitative platelet count adds independent information. The MPV has no additional effect on survival in patients with RARS.