Allogeneic hematopoietic stem cell transplantation for isolated and leukemic myeloid sarcoma in adults: a report from the Acute Leukemia Working Party of the European group for Blood and Marrow Transplantation

Letters to the Editor ATO/ATRA without HSCT represents a valid and potentially curative therapeutic option for relapsed APL. Based on the characteristics of our series, this assumption might particularly apply to patients who are treated with this regimen for late relapse. This parameter, together with patient decision to refuse HSCT and advanced age in some cases, was the criterion for assessing the efficacy of the prolonged ATO/ATRA combination in relapsed APL. The French group reported a randomized study on 20 relapsed APL patients who received ATO alone or in combination with ATRA, showing that 80% of patients achieved hematologic CR after one cycle. 6 On the other hand, a recent update of the Estey study 3 which first reported this regimen in newly diagnosed patients, demonstrated considerable efficacy with excellent outcome in particular for non-high risk APL. As an additional cautionary criterion, all patients in the present series were closely monitored by Rt-PCR in order to allow pre-emptive therapeutic intervention and the use of HSCT in case of a further molecular relapse. Of note, previously reported UPN 6 delivered a healthy baby after ATO/ATRA salvage, 5 and her second CR currently already exceeds the duration of first CR induced by ATRA and chemotherapy. Our results are comparable to those obtained in a recently reported series of 13 patients who received autologous HSCT in second molecular CR. In that study, relapses were hematologic in 12 cases and molecular in one case. All patients were treated with chemotherapy and after consolidation all achieved CRm: 10 of 13 patients (77%) were alive and well after a median follow up of 25 months from second CR 8 . We report here similar results with an ATO-based salvage therapy, with 88% of patients remaining in prolonged CRm without transplant procedures. Further studies in larger series are warranted to better establish whether autologous and allogeneic HSCT might be avoided in patients with late relapse APL receiving a prolonged ATO plus ATRA therapy.