Long Term Follow up Analysis Following Front Line Therapy with Dexamethasone or Dexamethasone Plus Rituximab in Adults with Primary Immune Thrombocytopenia.

Abstract 2415

Poster Board II-392

We previously reported that in adults with primary immune thrombocytopenia (ITP) the addition of four weekly administrations of rituximab 375 mg/m² to a single course of dexamethasone (40 mg daily for four days) improves the rate of sustained response (SR, i.e. platelet count ³ 50 × 10⁹/L at month 6 from the beginning of treatment) if compared with dexamethasone alone (63% vs 36%, P= 0.004, 95% C.I.: [0.079-0.455]) (ML18542 study, Zaja et al. Blood 2008; 112:Abstract 1). Moreover, the rate of SR in 27 patients receiving dexamethasone plus rituximab salvage therapy because of primary refractoriness or relapse after dexamethasone monotherapy was 56%. In order to better address the impact of therapy beyond month 6, a subsequent observational follow-up study up which lasted from month 6 up to month 36 was planned. Participating centers were asked to continue to monitor the patients enrolled in the ML18542 study at least every 4 months up to the end of year 3 from accrual, documenting the occurrence of delayed side effects, the response status and the need for further treatment. We considered as efficacy parameters the duration of response (RD), i.e. the interval between achievement of SR and relapse, the relapse rate (number of patients who lost their SR status) and the need of further specific anti ITP therapy after month 6 (TFS). Eighty out of the original 101 patients enrolled in the ML18542 study, 15 treated with the dexamethasone monotherapy arm, 41 with the dexamethasone plus rituximab arm and 24 who received dexamethasone plus rituximab salvage therapy, were systematically followed-up beyond month 6 for a median overall period of observation of 20 months (range: 4-40 months). Twenty-one patients could not be valuable, most of them because lost at follow up during the study period. As far as the safety profile, we documented one single case of Herpes Zoster reactivation at month 22 in a patient initially allocated to the dexamethasone arm who further received dexamethasone plus rituximab salvage therapy. No other infectious, delayed toxic events or deaths were registered. Fifty-three out 80 patients who achieved a SR according to the study protocol could be evaluated for long term efficacy. This group included 13 patients from the dexamethasone monotherapy arm who were observed after month 6 for a median period of 20 months (range: 12-28 months), 26 of dexamethasone plus rituximab arm observed for a median period of 24 months (range: 8-40 months), and 14 from the dexamethasone plus rituximab salvage therapy group observed for a median period of 20 months (range: 12-34). The rate of relapse in the three groups was 23% (3/13), 23% (6/26), and 14% (2/14) respectively (Fisher test, P= 0.824). The 30 months estimated probability of RD within each of the three treatment groups was 77%, 71%, and 85% (Log-rank test, P= 0.755), respectively. The time of SR loss was comprised between month 4 and 30 in the dexamethasone monotherapy arm, month 4 and 40 in the experimental arm, and month 8 and 34 in the salvage therapy arm. In these three groups, the use of further specific anti ITP therapy after month 6 was registered in 33%, 29% and 36% of patients (Fisher test, P= 1), respectively. Overall, in this period of observation 4 out 80 (5%) valuable patients underwent splenectomy. In conclusion the results of this study indicate: i) similar and very low pattern of long term toxicity between ITP patients treated either with single course of dexamethasone or dexamethasone plus rituximab; ii) no significant differences in the relapse rate, RD and TFS among patients who achieved SR after dexamethasone monotherapy or dexamethasone plus rituximab, either front line or salvage therapy, suggesting that relapse rate may be a possible surrogate of SR, rather than of the initial therapeutic choice.